Science.gov

Sample records for nitrogen fixation studies

  1. Update: Biological Nitrogen Fixation.

    ERIC Educational Resources Information Center

    Wiseman, Alan; And Others

    1985-01-01

    Updates knowledge on nitrogen fixation, indicating that investigation of free-living nitrogen-fixing organisms is proving useful in understanding bacterial partners and is expected to lead to development of more effective symbioses. Specific areas considered include biochemistry/genetics, synthesis control, proteins and enzymes, symbiotic systems,…

  2. The Fixation of Nitrogen.

    ERIC Educational Resources Information Center

    Andrew, S. P. S.

    1978-01-01

    Discusses the fixation of atmospheric nitrogen in the form of ammonia as one of the foundations of modern chemical industry. The article describes ammonia production and synthesis, purifying the hydrogen-nitrogen mix, nitric acid production, and its commericial plant. (HM)

  3. Molecular Biology of Nitrogen Fixation

    ERIC Educational Resources Information Center

    Shanmugam, K. T.; Valentine, Raymond C.

    1975-01-01

    Reports that as a result of our increasing knowledge of the molecular biology of nitrogen fixation it might eventually be possible to increase the biological production of nitrogenous fertilizer from atmospheric nitrogen. (GS)

  4. Nitrogen fixation apparatus

    DOEpatents

    Chen, Hao-Lin

    1984-01-01

    A method and apparatus for achieving nitrogen fixation includes a volumetric electric discharge chamber. The volumetric discharge chamber provides an even distribution of an electron beam, and enables the chamber to be maintained at a controlled energy to pressure (E/p) ratio. An E/p ratio of from 5 to 15 kV/atm of O.sub.2 /cm promotes the formation of vibrationally excited N.sub.2. Atomic oxygen interacts with vibrationally excited N.sub.2 at a much quicker rate than unexcited N.sub.2, greatly improving the rate at which NO is formed.

  5. Ammonia fixation by humic substances: A nitrogen-15 and carbon-13 NMR study

    USGS Publications Warehouse

    Thorn, K.A.; Mikita, M.A.

    1992-01-01

    The process of ammonia fixation has been studied in three well characterized and structurally diverse fulvic and humic acid samples. The Suwannee River fulvic acid, and the IHSS peat and leonardite humic acids, were reacted with 15N-labelled ammonium hydroxide, and analyzed by liquid phase 15N NMR spectrometry. Elemental analyses and liquid phase 13C NMR spectra also were recorded on the samples before and after reaction with ammonium hydroxide. The largest increase in percent nitrogen occurred with the Suwannee River fulvic acid, which had a nitrogen content of 0.88% before fixation and 3.17% after fixation. The 15N NMR spectra revealed that ammonia reacted similarly with all three samples, indicating that the functional groups which react with ammonia exist in structural configurations common to all three samples. The majority of nitrogcn incorporated into the samples appears to be in the form of indole and pyrrole nitrogen, followed by pyridine, pyrazine, amide and aminohydroquinone nitrogen. Chemical changes in the individual samples upon fixation could not be discerned from the 13C NMR spectra.

  6. Eighth international congress on nitrogen fixation

    SciTech Connect

    Not Available

    1990-01-01

    This volume contains the proceedings of the Eighth International Congress on Nitrogen Fixation held May 20--26, 1990 in Knoxville, Tennessee. The volume contains abstracts of individual presentations. Sessions were entitled Recent Advances in the Chemistry of Nitrogen Fixation, Plant-microbe Interactions, Limiting Factors of Nitrogen Fixation, Nitrogen Fixation and the Environment, Bacterial Systems, Nitrogen Fixation in Agriculture and Industry, Plant Function, and Nitrogen Fixation and Evolution.

  7. Understanding Nitrogen Fixation

    SciTech Connect

    Paul J. Chirik

    2012-05-25

    synthesis of ammonia, NH{sub 3}, from its elements, H{sub 2} and N{sub 2}, via the venerable Haber-Bosch process is one of the most significant technological achievements of the past century. Our research program seeks to discover new transition metal reagents and catalysts to disrupt the strong N {triple_bond} N bond in N{sub 2} and create new, fundamental chemical linkages for the construction of molecules with application as fuels, fertilizers and fine chemicals. With DOE support, our group has discovered a mild method for ammonia synthesis in solution as well as new methods for the construction of nitrogen-carbon bonds directly from N{sub 2}. Ideally these achievements will evolve into more efficient nitrogen fixation schemes that circumvent the high energy demands of industrial ammonia synthesis. Industrially, atmospheric nitrogen enters the synthetic cycle by the well-established Haber-Bosch process whereby N{sub 2} is hydrogenated to ammonia at high temperature and pressure. The commercialization of this reaction represents one of the greatest technological achievements of the 20th century as Haber-Bosch ammonia is responsible for supporting approximately 50% of the world's population and serves as the source of half of the nitrogen in the human body. The extreme reaction conditions required for an economical process have significant energy consequences, consuming 1% of the world's energy supply mostly in the form of pollution-intensive coal. Moreover, industrial H{sub 2} synthesis via the water gas shift reaction and the steam reforming of methane is fossil fuel intensive and produces CO{sub 2} as a byproduct. New synthetic methods that promote this thermodynamically favored transformation ({Delta}G{sup o} = -4.1 kcal/mol) under milder conditions or completely obviate it are therefore desirable. Most nitrogen-containing organic molecules are derived from ammonia (and hence rely on the Haber-Bosch and H{sub 2} synthesis processes) and direct synthesis from

  8. Molecular Ecological and Stable Isotopic Studies of Nitrogen Fixation in Modern Microbial Mats

    NASA Technical Reports Server (NTRS)

    Bebout, B. M.; Crumbliss, L. L.; DesMarais, D. J.; Hogan, M. E.; Omoregie, E.; Turk, K. A.; Zehr, J. P.

    2003-01-01

    Nitrogen is usually the element limiting biological productivity in the marine environment. Microbial mats, laminated microbial communities analogous to some of the oldest forms of life on Earth, are often the sites of high rates of N fixation (the energetically expensive conversion of atmospheric dinitrogen into a biologically useful form). The N fixing enzyme nitrogenase is generally considered to be of ancient origin, and is widely distributed throughout the Bacterial and Archaeal domains of life, indicating an important role for this process over evolutionary time. The stable isotopic signature of N fixation is purportedly recognizable in organic matter (ancient kerogens as well as present-day microbial mats) as a delta (15)N(sub organic) near zero. We studied two microbial mats exhibiting different rates of N fixation in order to better understand the impact of N fixation on the delta (15)N (sub organic) of the mats, as well as what organisms are important in this process. Mats dominated by the cyanobacterium Microcoleus chthonoplastes grow in permanently submerged hypersaline salterns, and exhibit low rates of N fixation, whereas mats dominated by the cyanobacterium Lyngbya spp grow in an intertidal area, and exhibit rates of N fixation an order of magnitude higher. To examine successional stages in mat growth, both developing and established mats at each location were sampled. PCR and RT-PCR based approaches were used to identify, respectively, the organisms containing nifH (one of the genes that encode nitrogenase) as well as those expressing nifH in these mats. Both mats exhibited a distinct diel cycle of N fixation, with highest rates occurring at night. The delta (15)N(sub organic) of the subtidal Microcoleus mats is near zero whereas the delta (15)N(sub organic) is slightly more positive (+ 2-3%), in the intertidal Lyngbya mats, an interesting difference in view of the fact that overall rates of activity in the intertidal mats are much higher that those

  9. Missing nitrogen fixation in the Benguela region

    NASA Astrophysics Data System (ADS)

    Wasmund, Norbert; Struck, Ulrich; Hansen, Anja; Flohr, Anita; Nausch, Günther; Grüttmüller, Annett; Voss, Maren

    2015-12-01

    Opposing opinions on the importance of nitrogen fixation in the northern Benguela upwelling region provoked us to investigate the magnitude of nitrogen fixation in front of northern Namibia and southern Angola. Measurements of nitrogen fixation rates using the 15N method at 66 stations during seven cruises from 2008 to 2014 showed that, in general, the 15N content in the biomass did not increase after tracer incubation with 15N2, indicating that no nitrogen fixation occurred. Correspondingly, the filamentous nitrogen-fixing cyanobacterium Trichodesmium was almost not present. The abundant picocyanobacteria did obviously not perform nitrogen fixation to a significant degree. The artificial improvement of conditions for nitrogen fixation in mesocosm experiments, including phosphate and iron additions and a warmer temperature, failed to induce nitrogen fixation. A plausible explanation of these findings is a lack of conditioned cells for nitrogen fixation in the Benguela region.

  10. Trichodesmium and nitrogen fixation in the Kuroshio

    NASA Astrophysics Data System (ADS)

    Shiozaki, T.; Takeda, S.; Itoh, S.; Kodama, T.; Liu, X.; Hashihama, F.; Furuya, K.

    2015-07-01

    Nitrogen fixation in the Kuroshio influences nitrogen balance in the North Pacific Ocean. The genus Trichodesmium is recognized as a major diazotroph in the Kuroshio. Although its abundance is higher in the Kuroshio than in adjacent waters, the reason for this difference remains unclear. The present study investigated the abundance of Trichodesmium spp. and nitrogen fixation together with concentrations of dissolved iron and phosphate, whose availabilities potentially control diazotrophy, in the Kuroshio and its marginal seas. We performed the observations near the Miyako Islands, which form part of the Ryukyu Islands, situated along the Kuroshio, since satellite analysis suggested that material transport could occur from the islands to the Kuroshio. Trichodesmium spp. bloomed (> 20 000 filaments L-1) near the Miyako Islands, and the abundance was high in the Kuroshio and the Kuroshio bifurcation region of the East China Sea, but was low in the Philippine Sea. The abundance of Trichodesmium spp. was significantly correlated with the total nitrogen fixation activity. The surface concentrations of dissolved iron (0.19-0.89 nM) and phosphate (< 3-36 nM) were similar for all of the study areas, indicating that the nutrient distribution could not explain the spatial differences in Trichodesmium spp. abundance and nitrogen fixation. We used a numerical model to simulate the transportation of water around the Ryukyu Islands to the Kuroshio. Our results indicate that Trichodesmium growing around the islands situated along the Kuroshio is potentially important for determining diazotrophy in this region.

  11. Biochemical Approaches to Improved Nitrogen Fixation

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Improving symbiotic nitrogen fixation by legumes has emerged again as an important topic on the world scene due to the energy crisis and lack of access to nitrogen fertilizer in developing countries. We have taken a biochemical genomics approach to improving symbiotic nitrogen fixation in legumes. L...

  12. Nitrogen fixation method and apparatus

    DOEpatents

    Chen, H.L.

    1983-08-16

    A method and apparatus for achieving nitrogen fixation includes a volumetric electric discharge chamber. The volumetric discharge chamber provides an even distribution of an electron beam, and enables the chamber to be maintained at a controlled energy to pressure (E/p) ratio. An E/p ratio of from 5 to 15 kV/atm of O[sub 2]/cm promotes the formation of vibrationally excited N[sub 2]. Atomic oxygen interacts with vibrationally excited N[sub 2] at a much quicker rate than unexcited N[sub 2], greatly improving the rate at which NO is formed. 1 fig.

  13. Nitrogen fixation method and apparatus

    DOEpatents

    Chen, Hao-Lin

    1983-01-01

    A method and apparatus for achieving nitrogen fixation includes a volumetric electric discharge chamber. The volumetric discharge chamber provides an even distribution of an electron beam, and enables the chamber to be maintained at a controlled energy to pressure (E/p) ratio. An E/p ratio of from 5 to 15 kV/atm of O.sub.2 /cm promotes the formation of vibrationally excited N.sub.2. Atomic oxygen interacts with vibrationally excited N.sub.2 at a much quicker rate than unexcited N.sub.2, greatly improving the rate at which NO is formed.

  14. Methanotrophy Induces Nitrogen Fixation in Boreal Mosses

    NASA Astrophysics Data System (ADS)

    Tiirola, M. A.

    2014-12-01

    Many methanotrophic bacterial groups fix nitrogen in laboratory conditions. Furthermore, nitrogen (N) is a limiting nutrient in many environments where methane concentrations are highest. Despite these facts, methane-induced N fixation has previously been overlooked, possibly due to methodological problems. To study the possible link between methanotrophy and diazotrophy in terrestrial and aquatic habitats, we measured the co-occurrence of these two processes in boreal forest, peatland and stream mosses using a stable isotope labeling approach (15 N2 and 13 CH4 double labeling) and sequencing of the nifH gene marker. N fixation associated with forest mosses was dependent on the annual N deposition, whereas methane stimulate N fixation neither in high (>3 kg N ha -1 yr -1) nor low deposition areas, which was in accordance with the nifH gene sequencing showing that forest mosses (Pleurozium schreberi and Hylocomium splendens ) carried mainly cyanobacterial N fixers. On the other extreme, in stream mosses (Fontinalis sp.) methane was actively oxidized throughout the year, whereas N fixation showed seasonal fluctuation. The co-occurrence of the two processes in single cell level was proven by co-localizing both N and methane-carbon fixation with the secondary ion mass spectrometry (SIMS) approach. Methanotrophy and diazotrophy was also studied in peatlands of different primary successional stages in the land-uplift coast of Bothnian Bay, in the Siikajoki chronosequence, where N accumulation rates in peat profiles indicate significant N fixation. Based on experimental evidence it was counted that methane-induced N fixation explained over one-third of the new N input in the younger peatland successional stages, where the highest N fixation rates and highest methane oxidation activities co-occurred in the water-submerged Sphagnum moss vegetation. The linkage between methanotrophic carbon cycling and N fixation may therefore constitute an important mechanism in the rapid

  15. Nitrogen fixation and nitrogen transformations in marine symbioses.

    PubMed

    Fiore, Cara L; Jarett, Jessica K; Olson, Nathan D; Lesser, Michael P

    2010-10-01

    Many marine organisms have coevolved symbiotic relationships with nitrogen-fixing bacteria in nitrogen limited environments such as coral reefs. In addition, some of these organisms also harbor microbes that carry out nitrification and denitrification. Prokaryotes involved in nitrogen fixation and other nitrogen transformations are symbionts in a range of eukaryotic hosts in the marine environment including shipworms, diatoms, corals and sponges. Molecular genetic approaches, and other analytical techniques, have provided exciting new insights into symbiont diversity and the relationship between host and symbiont. We review the current state of knowledge of these symbioses and highlight important avenues for future studies. PMID:20674366

  16. Variable Nitrogen Fixation in Wild Populus

    PubMed Central

    Doty, Sharon L.; Sher, Andrew W.; Fleck, Neil D.; Khorasani, Mahsa; Bumgarner, Roger E.; Khan, Zareen; Ko, Andrew W. K.; Kim, Soo-Hyung; DeLuca, Thomas H.

    2016-01-01

    The microbiome of plants is diverse, and like that of animals, is important for overall health and nutrient acquisition. In legumes and actinorhizal plants, a portion of essential nitrogen (N) is obtained through symbiosis with nodule-inhabiting, N2-fixing microorganisms. However, a variety of non-nodulating plant species can also thrive in natural, low-N settings. Some of these species may rely on endophytes, microorganisms that live within plants, to fix N2 gas into usable forms. Here we report the first direct evidence of N2 fixation in the early successional wild tree, Populus trichocarpa, a non-leguminous tree, from its native riparian habitat. In order to measure N2 fixation, surface-sterilized cuttings of wild poplar were assayed using both 15N2 incorporation and the commonly used acetylene reduction assay. The 15N label was incorporated at high levels in a subset of cuttings, suggesting a high level of N-fixation. Similarly, acetylene was reduced to ethylene in some samples. The microbiota of the cuttings was highly variable, both in numbers of cultured bacteria and in genetic diversity. Our results indicated that associative N2-fixation occurred within wild poplar and that a non-uniformity in the distribution of endophytic bacteria may explain the variability in N-fixation activity. These results point to the need for molecular studies to decipher the required microbial consortia and conditions for effective endophytic N2-fixation in trees. PMID:27196608

  17. Variable Nitrogen Fixation in Wild Populus.

    PubMed

    Doty, Sharon L; Sher, Andrew W; Fleck, Neil D; Khorasani, Mahsa; Bumgarner, Roger E; Khan, Zareen; Ko, Andrew W K; Kim, Soo-Hyung; DeLuca, Thomas H

    2016-01-01

    The microbiome of plants is diverse, and like that of animals, is important for overall health and nutrient acquisition. In legumes and actinorhizal plants, a portion of essential nitrogen (N) is obtained through symbiosis with nodule-inhabiting, N2-fixing microorganisms. However, a variety of non-nodulating plant species can also thrive in natural, low-N settings. Some of these species may rely on endophytes, microorganisms that live within plants, to fix N2 gas into usable forms. Here we report the first direct evidence of N2 fixation in the early successional wild tree, Populus trichocarpa, a non-leguminous tree, from its native riparian habitat. In order to measure N2 fixation, surface-sterilized cuttings of wild poplar were assayed using both 15N2 incorporation and the commonly used acetylene reduction assay. The 15N label was incorporated at high levels in a subset of cuttings, suggesting a high level of N-fixation. Similarly, acetylene was reduced to ethylene in some samples. The microbiota of the cuttings was highly variable, both in numbers of cultured bacteria and in genetic diversity. Our results indicated that associative N2-fixation occurred within wild poplar and that a non-uniformity in the distribution of endophytic bacteria may explain the variability in N-fixation activity. These results point to the need for molecular studies to decipher the required microbial consortia and conditions for effective endophytic N2-fixation in trees. PMID:27196608

  18. Cultivar effects on nitrogen fixation in peas and lentils

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Increasing nitrogen fixation in legume crops could increase cropping productivity and reduce nitrogen fertilizer use. Studies have found that crop genotype, rhizobial strain, and occasionally genotype-specific interactions affect N fixation, but this knowledge has not yet been used to evaluate or br...

  19. Eighth international congress on nitrogen fixation. Final program

    SciTech Connect

    Not Available

    1990-12-31

    This volume contains the proceedings of the Eighth International Congress on Nitrogen Fixation held May 20--26, 1990 in Knoxville, Tennessee. The volume contains abstracts of individual presentations. Sessions were entitled Recent Advances in the Chemistry of Nitrogen Fixation, Plant-microbe Interactions, Limiting Factors of Nitrogen Fixation, Nitrogen Fixation and the Environment, Bacterial Systems, Nitrogen Fixation in Agriculture and Industry, Plant Function, and Nitrogen Fixation and Evolution.

  20. Nitrogen Fixation in Denitrified Marine Waters

    PubMed Central

    Fernandez, Camila; Farías, Laura; Ulloa, Osvaldo

    2011-01-01

    Nitrogen fixation is an essential process that biologically transforms atmospheric dinitrogen gas to ammonia, therefore compensating for nitrogen losses occurring via denitrification and anammox. Currently, inputs and losses of nitrogen to the ocean resulting from these processes are thought to be spatially separated: nitrogen fixation takes place primarily in open ocean environments (mainly through diazotrophic cyanobacteria), whereas nitrogen losses occur in oxygen-depleted intermediate waters and sediments (mostly via denitrifying and anammox bacteria). Here we report on rates of nitrogen fixation obtained during two oceanographic cruises in 2005 and 2007 in the eastern tropical South Pacific (ETSP), a region characterized by the presence of coastal upwelling and a major permanent oxygen minimum zone (OMZ). Our results show significant rates of nitrogen fixation in the water column; however, integrated rates from the surface down to 120 m varied by ∼30 fold between cruises (7.5±4.6 versus 190±82.3 µmol m−2 d−1). Moreover, rates were measured down to 400 m depth in 2007, indicating that the contribution to the integrated rates of the subsurface oxygen-deficient layer was ∼5 times higher (574±294 µmol m−2 d−1) than the oxic euphotic layer (48±68 µmol m−2 d−1). Concurrent molecular measurements detected the dinitrogenase reductase gene nifH in surface and subsurface waters. Phylogenetic analysis of the nifH sequences showed the presence of a diverse diazotrophic community at the time of the highest measured nitrogen fixation rates. Our results thus demonstrate the occurrence of nitrogen fixation in nutrient-rich coastal upwelling systems and, importantly, within the underlying OMZ. They also suggest that nitrogen fixation is a widespread process that can sporadically provide a supplementary source of fixed nitrogen in these regions. PMID:21687726

  1. Effects of model structural uncertainty on carbon cycle projections: biological nitrogen fixation as a case study

    NASA Astrophysics Data System (ADS)

    Wieder, William R.; Cleveland, Cory C.; Lawrence, David M.; Bonan, Gordon B.

    2015-04-01

    Uncertainties in terrestrial carbon (C) cycle projections increase uncertainty of potential climate feedbacks. Efforts to improve model performance often include increased representation of biogeochemical processes, such as coupled carbon-nitrogen (N) cycles. In doing so, models are becoming more complex, generating structural uncertainties in model form that reflect incomplete knowledge of how to represent underlying processes. Here, we explore structural uncertainties associated with biological nitrogen fixation (BNF) and quantify their effects on C cycle projections. We find that alternative plausible structures to represent BNF result in nearly equivalent terrestrial C fluxes and pools through the twentieth century, but the strength of the terrestrial C sink varies by nearly a third (50 Pg C) by the end of the twenty-first century under a business-as-usual climate change scenario representative concentration pathway 8.5. These results indicate that actual uncertainty in future C cycle projections may be larger than previously estimated, and this uncertainty will limit C cycle projections until model structures can be evaluated and refined.

  2. Biological Nitrogen Fixation In Tropical Dry Forests Of Costa Rica

    NASA Astrophysics Data System (ADS)

    Gei, M. G.; Powers, J. S.

    2012-12-01

    Evidence suggests that tropical dry forests (TDF) are not nitrogen (N) deficient. This evidence includes: high losses of gaseous nitrogen during the rainy season, high ecosystem soil N stocks and high N concentrations in leaves and litterfall. Its been commonly hypothesized that biological nitrogen fixation is responsible for the high availability of N in tropical soils. However, the magnitude of this flux has rarely if ever been measured in tropical dry forests. Because of the high cost of fixing N and the ubiquity of N fixing legume trees in the TDF, at the individual tree level symbiotic fixation should be a strategy down-regulated by the plant. Our main goal was to determine the rates of and controls over symbiotic N fixation. We hypothesized that legume tree species employ a facultative strategy of nitrogen fixation and that this process responds to changes in light availability, soil moisture and nutrient supply. We tested this hypothesis both on naturally established trees in a forest and under controlled conditions in a shade house by estimating the quantities of N fixed annually using the 15N natural abundance method, counting nodules, and quantifying (field) or manipulating (shade house) the variation in important environmental variables (soil nutrients, soil moisture, and light). We found that in both in our shade house experiment and in the forest, nodulation varied among different legume species. For both settings, the 15N natural abundance approach successfully detected differences in nitrogen fixation among species. The legume species that we studied were able to regulate fixation depending on the environmental conditions. They showed to have different strategies of nitrogen fixation that follow a gradient of facultative to obligate fixation. Our data suggest that there exists a continuum of nitrogen fixation strategies among species. Any efforts to define tropical legume trees as a functional group need to incorporate this variation.

  3. Nitrogen Inputs via Nitrogen Fixation in Northern Plants and Soils

    NASA Astrophysics Data System (ADS)

    Thorp, N. R.; Wieder, R. K.; Vile, M. A.

    2015-12-01

    Dominated by cold and often acidic water logged environments, mineralization of organic matter is slow in the majority of northern ecosystems. Measures of extractable ammonium and nitrate are generally low and can be undetectable in peat pore waters. Despite this apparent nitrogen limitation, many of these environments produce deep deposits of soil organic matter. Biological nitrogen fixation carried out by autotrophic and heterotrophic diazotrophs associated with cryptograms provides the majority of known nitrogen inputs in these northern ecosystems. Nitrogen fixation was assessed in a variety of northern soils within rhizospheres of dominant plant communities. We investigated the availability of this newly fixed nitrogen to the vascular plant community in nitrogen limited northern plant communities. We tracked nitrogen flow from 15N2 gas fixed in Sphagnum mosses into tissues of two native vascular plant species, boreal cranberry (Vaccinium oxycoccus) and black spruce (Picea mariana). 15N-labeled Sphagnum microcosms were grown within variable mesh size exclusion/inclusion fabrics in a nitrogen addition experiment in situ in order to investigate the role of mycorrhizal fungi in the uptake of newly fixed nitrogen. Up to 24% of daily fixed 15N label was transferred to vascular plant tissues during 2 months. Nitrogen addition resulted in decreased N2 fixation rates; however, with higher nitrogen availability there was a higher rate of 15N label uptake into the vascular plants, likely the result of increased production of dissolved organic nitrogen. Reliance on mycorrhizal networks for nitrogen acquisition was indicated by nitrogen isotope fractionation patterns. Moreover, N2 fixation activities in mosses were stimulated when vascular plants were grown in moss microcosms versus "moss only" treatments. Results indicate that bog vascular plants may derive considerable nitrogen from atmospheric N2 biologically fixed within Sphagnum mosses. This work demonstrates that

  4. A Mathematic Approach to Nitrogen Fixation Through Earth History

    NASA Astrophysics Data System (ADS)

    Delgado-Bonal, Alfonso; Martín-Torres, F. Javier

    Nitrogen is essential for life as we know it. According to phylogenetic studies, all organisms capable of fixing nitrogen are prokaryotes, both bacteria and archaea, suggesting that nitrogen fixation and ammonium assimilation were metabolic features of the Last Universal Common Ancestor of all organisms. At present time the amount of biologically fixed nitrogen is around 2 × 1{0}^{13} g/year (Falkowski 1997), an amount much larger than the corresponding to the nitrogen fixed abiotically (between 2. 6 ×109 and 3 × 1{0}^{11} g/year) (Navarro-González et al. 2001). The current amount of nitrogen fixed is much higher than it was on Earth before the Cambrian explosion, where the symbiotic associations with leguminous plants, the major nitrogen fixer currently, did not exist and nitrogen was fixed only by free-living organisms as cyanobacteria. It has been suggested (Navarro-González et al. 2001) that abiotic sources of nitrogen fixation during Early Earth times could have an important role triggering a selection pressure favoring the evolution of nitrogenase and an increase in the nitrogen fixation rate. In this study we present briefly a method to analyze the amount of fixed nitrogen, both biotic and abiotic, through Earth's history.

  5. Changes in North Atlantic nitrogen fixation controlled by ocean circulation.

    PubMed

    Straub, Marietta; Sigman, Daniel M; Ren, Haojia; Martínez-García, Alfredo; Meckler, A Nele; Hain, Mathis P; Haug, Gerald H

    2013-09-12

    In the ocean, the chemical forms of nitrogen that are readily available for biological use (known collectively as 'fixed' nitrogen) fuel the global phytoplankton productivity that exports carbon to the deep ocean. Accordingly, variation in the oceanic fixed nitrogen reservoir has been proposed as a cause of glacial-interglacial changes in atmospheric carbon dioxide concentration. Marine nitrogen fixation, which produces most of the ocean's fixed nitrogen, is thought to be affected by multiple factors, including ocean temperature and the availability of iron and phosphorus. Here we reconstruct changes in North Atlantic nitrogen fixation over the past 160,000 years from the shell-bound nitrogen isotope ratio ((15)N/(14)N) of planktonic foraminifera in Caribbean Sea sediments. The observed changes cannot be explained by reconstructed changes in temperature, the supply of (iron-bearing) dust or water column denitrification. We identify a strong, roughly 23,000-year cycle in nitrogen fixation and suggest that it is a response to orbitally driven changes in equatorial Atlantic upwelling, which imports 'excess' phosphorus (phosphorus in stoichiometric excess of fixed nitrogen) into the tropical North Atlantic surface. In addition, we find that nitrogen fixation was reduced during glacial stages 6 and 4, when North Atlantic Deep Water had shoaled to become glacial North Atlantic intermediate water, which isolated the Atlantic thermocline from excess phosphorus-rich mid-depth waters that today enter from the Southern Ocean. Although modern studies have yielded diverse views of the controls on nitrogen fixation, our palaeobiogeochemical data suggest that excess phosphorus is the master variable in the North Atlantic Ocean and indicate that the variations in its supply over the most recent glacial cycle were dominated by the response of regional ocean circulation to the orbital cycles. PMID:23965620

  6. Nitrogen Fixation and Hydrogen Metabolism in Cyanobacteria

    PubMed Central

    Bothe, Hermann; Schmitz, Oliver; Yates, M. Geoffrey; Newton, William E.

    2010-01-01

    Summary: This review summarizes recent aspects of (di)nitrogen fixation and (di)hydrogen metabolism, with emphasis on cyanobacteria. These organisms possess several types of the enzyme complexes catalyzing N2 fixation and/or H2 formation or oxidation, namely, two Mo nitrogenases, a V nitrogenase, and two hydrogenases. The two cyanobacterial Ni hydrogenases are differentiated as either uptake or bidirectional hydrogenases. The different forms of both the nitrogenases and hydrogenases are encoded by different sets of genes, and their organization on the chromosome can vary from one cyanobacterium to another. Factors regulating the expression of these genes are emerging from recent studies. New ideas on the potential physiological and ecological roles of nitrogenases and hydrogenases are presented. There is a renewed interest in exploiting cyanobacteria in solar energy conversion programs to generate H2 as a source of combustible energy. To enhance the rates of H2 production, the emphasis perhaps needs not to be on more efficient hydrogenases and nitrogenases or on the transfer of foreign enzymes into cyanobacteria. A likely better strategy is to exploit the use of radiant solar energy by the photosynthetic electron transport system to enhance the rates of H2 formation and so improve the chances of utilizing cyanobacteria as a source for the generation of clean energy. PMID:21119016

  7. Nitrogen Fixation: An Interdisciplinary Frontier

    ERIC Educational Resources Information Center

    Schneller, Stewart W.

    1972-01-01

    Research has progressed from three major directions--biological, chemical, and non-enzymatic. Hopefully all three will converge and will explain not only the process, but also introduce new means for modifying the molecule to meet the nutritional needs of man in areas now incapable of self support without fixed nitrogen. (DF)

  8. Metabolic Reconstruction and Modeling of Nitrogen Fixation in Rhizobium etli

    PubMed Central

    Resendis-Antonio, Osbaldo; Reed, Jennifer L; Encarnación, Sergio; Collado-Vides, Julio; Palsson, Bernhard Ø

    2007-01-01

    Rhizobiaceas are bacteria that fix nitrogen during symbiosis with plants. This symbiotic relationship is crucial for the nitrogen cycle, and understanding symbiotic mechanisms is a scientific challenge with direct applications in agronomy and plant development. Rhizobium etli is a bacteria which provides legumes with ammonia (among other chemical compounds), thereby stimulating plant growth. A genome-scale approach, integrating the biochemical information available for R. etli, constitutes an important step toward understanding the symbiotic relationship and its possible improvement. In this work we present a genome-scale metabolic reconstruction (iOR363) for R. etli CFN42, which includes 387 metabolic and transport reactions across 26 metabolic pathways. This model was used to analyze the physiological capabilities of R. etli during stages of nitrogen fixation. To study the physiological capacities in silico, an objective function was formulated to simulate symbiotic nitrogen fixation. Flux balance analysis (FBA) was performed, and the predicted active metabolic pathways agreed qualitatively with experimental observations. In addition, predictions for the effects of gene deletions during nitrogen fixation in Rhizobia in silico also agreed with reported experimental data. Overall, we present some evidence supporting that FBA of the reconstructed metabolic network for R. etli provides results that are in agreement with physiological observations. Thus, as for other organisms, the reconstructed genome-scale metabolic network provides an important framework which allows us to compare model predictions with experimental measurements and eventually generate hypotheses on ways to improve nitrogen fixation. PMID:17922569

  9. Nitrogen fixation: key genetic regulatory mechanisms.

    PubMed

    Martinez-Argudo, I; Little, R; Shearer, N; Johnson, P; Dixon, R

    2005-02-01

    The necessity to respond to the level of fixed nitrogen and external oxygen concentrations and to provide sufficient energy for nitrogen fixation imposes common regulatory principles amongst diazotrophs. The NifL-NifA system in Azotobacter vinelandii integrates the signals of redox, fixed-nitrogen and carbon status to regulate nif transcription. Multidomain signalling interactions between NifL and NifA are modulated by redox changes, ligand binding and interaction with the signal-transduction protein GlnK. Under adverse redox conditions (excess oxygen) or when fixed nitrogen is in excess, NifL forms a complex with NifA in which transcriptional activation is prevented. Oxidized NifL forms a binary complex with NifA to inhibit NifA activity. When fixed nitrogen is in excess, the non-covalently modified form of GlnK interacts with NifL to promote the formation of a GlnK-NifL-NifA ternary complex. When the cell re-encounters favourable conditions for nitrogen fixation, it is necessary to deactivate the signals to ensure that the NifL-NifA complex is dissociated so that NifA is free to activate transcription. This is achieved through interactions with 2-oxoglutarate, a key metabolic signal of the carbon status, which binds to the N-terminal GAF (cGMP-specific and stimulated phosphodiesterases, Anabaena adenylate cyclases and Escherichia coli FhlA) domain of NifA. PMID:15667291

  10. Applying Reversible Mutations of Nodulation and Nitrogen-Fixation Genes to Study Social Cheating in Rhizobium etli-Legume Interaction

    PubMed Central

    Wang, Hui; Zhong, Zengtao; Zhu, Jun

    2013-01-01

    Mutualisms are common in nature, though these symbioses can be quite permeable to cheaters in situations where one individual parasitizes the other by discontinuing cooperation yet still exploits the benefits of the partnership. In the Rhizobium-legume system, there are two separate contexts, namely nodulation and nitrogen fixation processes, by which resident Rhizobium individuals can benefit by cheating. Here, we constructed reversible and irreversible mutations in key nodulation and nitrogen-fixation pathways of Rhizobium etli and compared their interaction with plant hosts Phaseolus vulgaris to that of wild type. We show that R. etli reversible mutants deficient in nodulation factor production are capable of intra-specific cheating, wherein mutants exploit other Rhizobium individuals capable of producing these factors. Similarly, we show that R. etli mutants are also capable of cheating inter-specifically, colonizing the host legume yet contributing nothing to the partnership in terms of nitrogen fixation. Our findings indicate that cheating is possible in both of these frameworks, seemingly without damaging the stability of the mutualism itself. These results may potentially help explain observations suggesting that legume plants are commonly infected by multiple bacterial lineages during the nodulation process. PMID:23922937

  11. Nitrogen fixation in the mucus of Red Sea corals.

    PubMed

    Grover, Renaud; Ferrier-Pagès, Christine; Maguer, Jean-François; Ezzat, Leila; Fine, Maoz

    2014-11-15

    Scleractinian corals are essential constituents of tropical reef ecological diversity. They live in close association with diazotrophs [dinitrogen (N2)-fixing microbes], which can fix high rates of N2. Whether corals benefit from this extrinsic nitrogen source is still under debate. Until now, N2 fixation rates have been indirectly estimated using the acetylene reduction assay, which does not permit assessment of the amount of nitrogen incorporated into the different compartments of the coral holobiont. In the present study, the (15)N2 technique was applied for the first time on three Red Sea coral species. Significant (15)N enrichment was measured in particles released by corals to the surrounding seawater. N2 fixation rates were species specific and as high as 1.6-2 ng N day(-1) l(-1). However, no significant enrichment was measured in the symbiotic dinoflagellates or the coral host tissues, suggesting that corals do not benefit from diazotrophic N2 fixation. PMID:25278474

  12. Genetic regulation of nitrogen fixation in rhizobia.

    PubMed Central

    Fischer, H M

    1994-01-01

    This review presents a comparison between the complex genetic regulatory networks that control nitrogen fixation in three representative rhizobial species, Rhizobium meliloti, Bradyrhizobium japonicum, and Azorhizobium caulinodans. Transcription of nitrogen fixation genes (nif and fix genes) in these bacteria is induced primarily by low-oxygen conditions. Low-oxygen sensing and transmission of this signal to the level of nif and fix gene expression involve at least five regulatory proteins, FixL, FixJ, FixK, NifA, and RpoN (sigma 54). The characteristic features of these proteins and their functions within species-specific regulatory pathways are described. Oxygen interferes with the activities of two transcriptional activators, FixJ and NifA. FixJ activity is modulated via phosphorylation-dephosphorylation by the cognate sensor hemoprotein FixL. In addition to the oxygen responsiveness of the NifA protein, synthesis of NifA is oxygen regulated at the level of transcription. This type of control includes FixLJ in R. meliloti and FixLJ-FixK in A. caulinodans or is brought about by autoregulation in B. japonicum. NifA, in concert with sigma 54 RNA polymerase, activates transcription from -24/-12-type promoters associated with nif and fix genes and additional genes that are not directly involved in nitrogen fixation. The FixK proteins constitute a subgroup of the Crp-Fnr family of bacterial regulators. Although the involvement of FixLJ and FixK in nifA regulation is remarkably different in the three rhizobial species discussed here, they constitute a regulatory cascade that uniformly controls the expression of genes (fixNOQP) encoding a distinct cytochrome oxidase complex probably required for bacterial respiration under low-oxygen conditions. In B. japonicum, the FixLJ-FixK cascade also controls genes for nitrate respiration and for one of two sigma 54 proteins. Images PMID:7968919

  13. WHITE LUPIN NITROGEN FIXATION UNDER PHOSPHORUS DEFICIENCY

    Technology Transfer Automated Retrieval System (TEKTRAN)

    White lupin is highly adapted to growth in a low P environment. The objective of the present study was to evaluate whether white lupin grown under P-stress has adaptations in nodulation and N2 fixation that facilitate continued functioning. Nodulated plants were grown in silica sand supplied with N-...

  14. Impact of titanium dioxide nanomaterials on nitrogen fixation rate and intracellular nitrogen storage in Anabaena variabilis.

    PubMed

    Cherchi, Carla; Gu, April Z

    2010-11-01

    This study comprehensively investigated the impact of titanium dioxide nanomaterials (nTiO(2)) exposure on cell growth, nitrogen fixation activity, and nitrogen storage dynamics in the primary producer cyanobacteria Anabaena variabilis at various dose concentrations and exposure time lengths. The results indicated that both growth rate (EC(50)-96 h of 0.62 mgTiO(2)/L) and nitrogen fixation activity (EC(50)-96 h of 0.4 mgTiO(2)/L) were inhibited by nTiO(2) exposure. The Hom's law (C(n)T(m)) was used as inactivation model to predict the concentration- and time-dependent inhibition of growth and nitrogen fixation activity. The kinetic parameters determined suggested that the time of exposure has a greater influence than the nTiO(2) concentration in toxicity. We observed, for the first time, that nTiO(2) induced a dose (concentration and time)-dependent increase in both the occurrence and intracellular levels of the nitrogen-rich cyanophycin grana proteins (CGPs). The results implied that CGPs may play an important role in the stress response mechanisms of nTiO(2) exposure and can serve as a toxicity assessment endpoint indicator. This study demonstrated that nitrogen-fixing activity could be hampered by the release of nTiO(2) in aquatic environments; therefore it potentially impacts important biogeochemical processes, such as carbon and nitrogen cycling. PMID:20853867

  15. Evaluation of kidney bean yield and nitrogen fixation under low soil nitrogen

    Technology Transfer Automated Retrieval System (TEKTRAN)

    U.S. Kidney bean cultivars as a group have limited genetic diversity. They also require more intensive crop management than most other bean market classes. The objective of this study was to evaluate biological nitrogen fixation and seed yield in a diverse group of kidney lines. A 250 line Andean be...

  16. Seasonal patterns of periphyton nitrogen fixation in calcareous wetlands

    NASA Astrophysics Data System (ADS)

    Liao, X.; Inglett, P.

    2011-12-01

    Periphyton mats are an ecologically important component of the Everglades ecosystem and plays various vital ecological functions. However, nitrogen fixation of periphyton, has received little attention throughout much of the Everglades system. The objective of this study was to characterize the seasonal pattern of periphyton N2 fixation in the Hole-in-the-Donut (HID) of Florida Everglades, where farmed marl prairie wetlands have been restored through complete soil removal (CSR) to reduce nutrient levels. Two restored areas (i.e., cleared in 2000 and 2003) and a reference (natural and unfarmed) marl prairie wetland sites were selected in the HID. Seven times of sampling were performed across the wet and dry season during the 2010 and 2011. The annual fixed nitrogen was approximately 0.4gN m-2 yr-1 in the restored sites which was higher in the reference site (~0.2gN m-2 yr-1). All the three sites showed similar seasonal patterns of N2 fixation that is higher values were observed in the wet season; but the peak value was one month later in reference sits (i.e., September) comparing to the restored areas (i.e., July). The peak of periphyton AR rates in the 2000- and 2003-restored areas appeared in July (i.e., wet season) within the range of 20-79 nmols g-1dw h-1 and 31-53nmols g-1dw h-1, respectively. In contrast, the peak of reference site was observed in September with the range of 2-5 nmols g-1dw h-1. Stable N isotopic ratios (i.e., δ15N) also varied with time but didn't show consistent seasonal pattern as nitrogen fixation. N2 fixation positively correlated with periphyton total phosphorus (TP) and negatively correlated with total nitrogen and phosphorus molar ratios (TN:TP), indicating that N2 fixation would be a indicator of nutrient limitation. In general, δ15N was negatively correlated with nitrogenase activity but the correlation became weakened in the wet season, especially in the flooded July and September, which would be explained by other environmental

  17. Uncertainties of Nitrogen Fixation in a Dynamic Global Vegetation Model

    NASA Astrophysics Data System (ADS)

    Steinkamp, Joerg; Werner, Christian; Weber, Bettina; Hickler, Thomas

    2015-04-01

    Nitrogen is an essential nutrient for life on earth. However, most of it is in the form of dinitrogen (N2) unutilizable to life and only few organisms are able to break the triple bond, fix the nitrogen and thus make it available for cycling in the biosphere through "fixation". In most state-of-the-art dynamic global vegetation models (DGVMs) including a nitrogen cycle, N fixation is simulated by the Cleveland et al. (1999) algorithm (O-CN, LPJ-GUESS, CLM), that correlates annual N fixation to evapotranspiration rates or net primary production. Nevertheless, this algorithm has two major uncertainties, which are investigated by us: 1. The algorithm is based on annual fixation rates that are then applied uniformly throughout the year. However, in nature nitrogen fixation is an expensive process, which occurs only under favorable conditions. Here we compare the annual fixation values evenly distributed over the year with daily-derived fixation values based on a modified version of the Cleveland algorithm. We postulate that in higher latitudinal regions with seasonal climate as well as in regions with a distinct dry/wet season, modeled growth is enhanced by daily derived values compared to evenly distributed values, whereas in tropical regions hardly any difference will be visible. 2. One distinguishes between symbiotic and unsymbiotic nitrogen fixation, where the first one is associated with higher plants as symbionts supplying the fixers with carbohydrates, whereas the second, unsymbiotic is performed by so-called cryptogamic covers (CC). We found that the fixation by CC is underrepresented by the Cleveland algorithm, and a correction thus leads to enhanced growth in forested regions of higher latitudes that feature substantial CC fractions. Overall, the improvements of the algorithm proposed by us are expected to better reflect the reality of nitrogen fixation and cause an increased growth of vegetation, especially in higher northern latitudes.

  18. New insights into the evolutionary history of biological nitrogen fixation

    PubMed Central

    Boyd, Eric S.; Peters, John W.

    2013-01-01

    Nitrogenase, which catalyzes the ATP-dependent reduction of dinitrogen (N2) to ammonia (NH3), accounts for roughly half of the bioavailable nitrogen supporting extant life. The fundamental requirement for fixed forms of nitrogen for life on Earth, both at present and in the past, has led to broad and significant interest in the origin and evolution of biological N2 fixation. One key question is whether the limited availability of fixed nitrogen was a factor in life's origin or whether there were ample sources of fixed nitrogen produced by abiotic processes or delivered through the weathering of bolide impact materials to support this early life. If the latter, the key questions become what were the characteristics of the environment that precipitated the evolution of this oxygen sensitive process, when did this occur, and how was its subsequent evolutionary history impacted by the advent of oxygenic photosynthesis and the rise of oxygen in the Earth's biosphere. Since the availability of fixed sources of nitrogen capable of supporting early life is difficult to glean from the geologic record, there are limited means to get direct insights into these questions. Indirect insights, however, can be gained through phylogenetic studies of nitrogenase structural gene products and additional gene products involved in the biosynthesis of the complex metal-containing prosthetic groups associated with this enzyme complex. Insights gained from such studies, as reviewed herein, challenge traditional models for the evolution of biological nitrogen fixation and provide the basis for the development of new conceptual models that explain the stepwise evolution of this highly complex life sustaining process. PMID:23935594

  19. Nitrogen fixation control under drought stress. Localized or systemic?

    PubMed

    Marino, Daniel; Frendo, Pierre; Ladrera, Ruben; Zabalza, Ana; Puppo, Alain; Arrese-Igor, Cesar; González, Esther M

    2007-04-01

    Legume-Rhizobium nitrogen fixation is dramatically affected under drought and other environmental constraints. However, it has yet to be established as to whether such regulation of nitrogen fixation is only exerted at the whole-plant level (e.g. by a systemic nitrogen feedback mechanism) or can also occur at a local nodule level. To address this question, nodulated pea (Pisum sativum) plants were grown in a split-root system, which allowed for half of the root system to be irrigated at field capacity, while the other half was water deprived, thus provoking changes in the nodule water potential. Nitrogen fixation only declined in the water-deprived, half-root system and this result was correlated with modifications in the activities of key nodule's enzymes such as sucrose synthase and isocitrate dehydrogenase and in nodular malate content. Furthermore, the decline in nodule water potential resulted in a cell redox imbalance. The results also indicate that systemic nitrogen feedback signaling was not operating in these water-stressed plants, since nitrogen fixation activity was maintained at control values in the watered half of the split-root plants. Thus, the use of a partially droughted split-root system provides evidence that nitrogen fixation activity under drought stress is mainly controlled at the local level rather than by a systemic nitrogen signal. PMID:17416644

  20. Nitrogen fixation in Asaia sp. (family Acetobacteraceae).

    PubMed

    Samaddar, Neeloy; Paul, Arundhati; Chakravorty, Somnath; Chakraborty, Writachit; Mukherjee, Joydeep; Chowdhuri, Debarati; Gachhui, Ratan

    2011-08-01

    The genus Asaia (family Acetobacteraceae) was first introduced with a single species-Asaia bogorensis and later six more species were described namely A. siamensis, A. krungthepensis, A. lannaensis, A. platycodi, A. prunellae, and A. astilbes. Acetobacteraceae family has been divided into ten genera but, only three of them include nitrogen fixing species: Gluconacetobacter, Acetobacter, and Swaminathania. This article originated from our study primarily aimed to isolate new endosymbiotic nitrogen fixer among Acetobacteraceae during which we have isolated, for the first time in India, four different strains of Asaia sp. from three different sources: Michalia champaca flower, Anopheles mosquito, and ant Tetraponera rufonigra. All the endosymbiotic strains isolated possess the ability to fix nitrogen. Evidence for both nitrogenase activity and the presence of nifH gene in isolated Asaia sp. is presented. Asaia bogorensis (MTCC 4041(T)) and A. siamensis (MTCC 4042(T)), two of the validated type strains available from the repository, were tested positive for the presence of functional nitrogenase. The nifH gene sequences from these type strains were also confirmed and compared with other nitrogen fixing members of the family Acetobacteraceae. Our result corroborate with the previous reports that Asaia sp. are indeed widely distributed in nature but this is the first time demonstration of their functional nitrogenase activity. This study shows Asaia sp. as fourth genera of nitrogen fixing bacteria in the family Acetobacteraceae. PMID:21681635

  1. Novel regulatory cascades controlling expression of nitrogen-fixation genes in Geobacter sulfurreducens

    PubMed Central

    Ueki, Toshiyuki; Lovley, Derek R.

    2010-01-01

    Geobacter species often play an important role in bioremediation of environments contaminated with metals or organics and show promise for harvesting electricity from waste organic matter in microbial fuel cells. The ability of Geobacter species to fix atmospheric nitrogen is an important metabolic feature for these applications. We identified novel regulatory cascades controlling nitrogen-fixation gene expression in Geobacter sulfurreducens. Unlike the regulatory mechanisms known in other nitrogen-fixing microorganisms, nitrogen-fixation gene regulation in G. sulfurreducens is controlled by two two-component His–Asp phosphorelay systems. One of these systems appears to be the master regulatory system that activates transcription of the majority of nitrogen-fixation genes and represses a gene encoding glutamate dehydrogenase during nitrogen fixation. The other system whose expression is directly activated by the master regulatory system appears to control by antitermination the expression of a subset of the nitrogen-fixation genes whose transcription is activated by the master regulatory system and whose promoter contains transcription termination signals. This study provides a new paradigm for nitrogen-fixation gene regulation. PMID:20660485

  2. Diel nitrogen fixation by cyanobacterial surface blooms in sanctuary lake, pennsylvania.

    PubMed

    Storch, T A; Saunders, G W; Ostrofsky, M L

    1990-02-01

    Diel nitrogen fixation studies were conducted with assemblages of cyanobacteria sampled from surface blooms on Sanctuary Lake, Pa. The studies were conducted between July and September of 1982 to 1985 by using the acetylene reduction technique. Assemblages with the lowest cell concentrations (0.9 x 10 to 1.0 x 10 cells per liter) exhibited nitrogen fixation activity throughout the day, with maximum fixation rates occurring in mid to late afternoon; fixation proceeded throughout the night at rates equivalent to 23 to 28% of the afternoon maximum. In studies conducted with the highest cell concentrations (3.7 x 10 to 6.7 x 10 cells per liter), fixation rates reached maximum values in mid to late morning. The rates declined rapidly throughout the midday period and subsequently ceased from late afternoon until sunrise on the following day. The afternoon decline and cessation of fixation exhibited by high cell concentrations correlated with photosynthetically induced low total CO(2) and supersaturating O(2) concentrations. The midday decline could be prevented and partially reversed by experimentally lowering O(2) and increasing total CO(2) concentrations. Under experimental conditions which simultaneously prevented supersaturating O(2) concentrations and maintained high total CO(2) availability, nitrogen fixation continued throughout the solar day, with maximum rates occurring at midday. These observations indicate that temporal changes in photosynthetic activity may affect diel fluctuations in nitrogen fixation. PMID:16348120

  3. Oxygen relations of nitrogen fixation in cyanobacteria.

    PubMed Central

    Fay, P

    1992-01-01

    The enigmatic coexistence of O2-sensitive nitrogenase and O2-evolving photosynthesis in diazotrophic cyanobacteria has fascinated researchers for over two decades. Research efforts in the past 10 years have revealed a range of O2 sensitivity of nitrogenase in different strains of cyanobacteria and a variety of adaptations for the protection of nitrogenase from damage by both atmospheric and photosynthetic sources of O2. The most complex and apparently most efficient mechanisms for the protection of nitrogenase are incorporated in the heterocysts, the N2-fixing cells of cyanobacteria. Genetic studies indicate that the controls of heterocyst development and nitrogenase synthesis are closely interrelated and that the expression of N2 fixation (nif) genes is regulated by pO2. Images PMID:1620069

  4. Nitrogen fixation and the diazotroph community in the temperate coastal region of the northwestern North Pacific

    NASA Astrophysics Data System (ADS)

    Shiozaki, T.; Nagata, T.; Ijichi, M.; Furuya, K.

    2015-08-01

    Nitrogen fixation in temperate oceans is a potentially important, but poorly understood process that may influence the marine nitrogen budget. This study determined seasonal variations in nitrogen fixation and the diazotroph community within the euphotic zone in the temperate coastal region of the northwestern North Pacific. Nitrogen fixation as high as 13.6 nmol N L-1 d-1 was measured from early summer to fall when the surface temperature exceeded 14.2 °C (but was lower than 24.3 °C) and the surface nitrate concentration was low (≤ 0.30 μM), although we also detected nitrogen fixation in subsurface layers (42-62 m) where nitrate concentrations were high (> 1 μM). Clone library analysis results indicated that nifH gene sequences were omnipresent throughout the investigation period. During the period when nitrogen fixation was detected (early summer to fall), the genes affiliated with UCYN-A, Trichodesmium, and γ-proteobacterial phylotype γ-24774A11 were frequently recovered. In contrast, when nitrogen fixation was undetectable (winter to spring), many sequences affiliated with Cluster III diazotrophs (putative anaerobic bacteria) were recovered. Quantitative PCR analysis revealed that UCYN-A was relatively abundant from early to late summer compared with Trichodesmium and γ-24774A11, whereas Trichodesmium abundance was the highest among the three groups during fall.

  5. Nitrogen fixation potential in global chickpea mini-core collection

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Biological nitrogen fixation (BNF) is a sustainable alternative for nitrogen supply to agriculture worldwide. One approach to increasing BNF in agriculture is to breed and use legumes with greater BNF capacity. To assess the capacity for BNF in chickpea (Cicer arietinum) global germplasm, a genetica...

  6. The importance of regulation of nitrogen fixation

    NASA Astrophysics Data System (ADS)

    Menge, D. N.

    2012-12-01

    I am not a proponent of including more detail in models simply because it makes them more realistic. More complexity increases the difficulty of model interpretation, so it only makes sense to include complexity if its benefit exceeds its costs. Biological nitrogen (N) fixation (BNF) is one process for which I feel the benefits of including greater complexity far outweigh the costs. I don't think that just because I work on BNF; I work on BNF because I think that. BNF, a microbial process carried out by free-living and symbiotic microbes, is the dominant N input to many ecosystems, the primary mechanism by which N deficiency can feed back to N inputs, and a main mechanism by which N surplus can develop. The dynamics of BNF, therefore, have huge implications for the rate of carbon uptake and the extent of CO2 fertilization, as well as N export to waterways and N2O emissions to the atmosphere. Unfortunately, there are serious deficiencies in our understanding of BNF. One main deficiency in our understanding is the extent to which various symbiotic N fixing organisms respond to imbalanced nutrition. Theory suggests that these responses, which I will call "strategies," have fundamental consequences for N fixer niches and ecosystem-level N and C cycling. Organisms that fix N regardless of whether they need it, a strategy that I will call "obligate," occupy post-disturbance niches and rapidly lead to N surplus. On the contrary, organisms that only fix as much N as they need, a "facultative" strategy, can occupy a wider range of successional niches, do not produce surplus N, and respond more rapidly to increased atmospheric CO2. In this talk I will show new results showing that consideration of these strategies could on its own explain the latitudinal distribution of symbiotic N fixing trees in North America. Specifically, the transition in N-fixing tree abundance from ~10% of basal area south of 35° latitude to ~1% of basal area north of 35° latitude that we observe

  7. Low Carbon Costs of Nitrogen Fixation in Tropical Dry Forests

    NASA Astrophysics Data System (ADS)

    Gei, M. G.; Powers, J. S.

    2015-12-01

    Legume tree species with the ability to fix nitrogen (N) are highly diverse and widespread across tropical forests but in particular in the dry tropics. Their ecological success in lower latitudes has been called a "paradox": soil N in the tropics is thought to be high, while acquiring N through fixation incurs high energetic costs. However, the long held assumptions that N fixation is limited by photosynthate and that N fixation penalizes plant productivity have rarely been tested, particularly in legume tree species. We show results from three different experiments where we grew eleven species of tropical dry forest legumes. We quantified plant biomass and N fixation using nodulation and the 15N natural isotope abundance (Ndfa or nitrogen derived from fixation). These data show little evidence for costs of N fixation in seedlings grown under different soil fertility, light regimes, and with different microbial communities. Seedling productivity did not incur major costs because of N fixation: indeed, the average slope between Ndfa and biomass was positive (range in slopes: -0.03 to 0.3). Moreover, foliar N, which varied among species, was tightly constrained and not correlated with Ndfa. This finding implies that legume species have a target N that does not change depending on N acquisition strategies. The process of N fixation in tropical legumes may be more carbon efficient than previously thought. This view is more consistent with the hyperabundance of members of this family in tropical ecosystems.

  8. Buckminsterfullerenes: a non-metal system for nitrogen fixation.

    PubMed

    Nishibayashi, Yoshiaki; Saito, Makoto; Uemura, Sakae; Takekuma, Shin-Ichi; Takekuma, Hideko; Yoshida, Zen-Ichi

    2004-03-18

    In all nitrogen-fixation processes known so far--including the industrial Haber-Bosch process, biological fixation by nitrogenase enzymes and previously described homogeneous synthetic systems--the direct transformation of the stable, inert dinitrogen molecule (N2) into ammonia (NH3) relies on the powerful redox properties of metals. Here we show that nitrogen fixation can also be achieved by using a non-metallic buckminsterfullerene (C60) molecule, in the form of a water-soluble C60:gamma-cyclodextrin (1:2) complex, and light under nitrogen at atmospheric pressure. This metal-free system efficiently fixes nitrogen under mild conditions by making use of the redox properties of the fullerene derivative. PMID:15029186

  9. Low rates of nitrogen fixation in eastern tropical South Pacific surface waters.

    PubMed

    Knapp, Angela N; Casciotti, Karen L; Berelson, William M; Prokopenko, Maria G; Capone, Douglas G

    2016-04-19

    An extensive region of the Eastern Tropical South Pacific (ETSP) Ocean has surface waters that are nitrate-poor yet phosphate-rich. It has been proposed that this distribution of surface nutrients provides a geochemical niche favorable for N2fixation, the primary source of nitrogen to the ocean. Here, we present results from two cruises to the ETSP where rates of N2fixation and its contribution to export production were determined with a suite of geochemical and biological measurements. N2fixation was only detectable using nitrogen isotopic mass balances at two of six stations, and rates ranged from 0 to 23 µmol N m(-2)d(-1)based on sediment trap fluxes. Whereas the fractional importance of N2fixation did not change, the N2-fixation rates at these two stations were several-fold higher when scaled to other productivity metrics. Regardless of the choice of productivity metric these N2-fixation rates are low compared with other oligotrophic locations, and the nitrogen isotope budgets indicate that N2fixation supports no more than 20% of export production regionally. Although euphotic zone-integrated short-term N2-fixation rates were higher, up to 100 µmol N m(-2)d(-1), and detected N2fixation at all six stations, studies of nitrogenase gene abundance and expression from the same cruises align with the geochemical data and together indicate that N2fixation is a minor source of new nitrogen to surface waters of the ETSP. This finding is consistent with the hypothesis that, despite a relative abundance of phosphate, iron may limit N2fixation in the ETSP. PMID:26976587

  10. Fixation of nitrogen in the presence of water vapor

    DOEpatents

    Harteck, Paul

    1984-01-01

    A process for the fixation of nitrogen is disclosed which comprises combining a mixture of nitrogen, oxygen, metal oxide and water vapor, initially heating the combination to initiate a reaction which forms nitrate, but at a temperature and pressure range below the dissociation pressure of the nitrate. With or without the water component, the yield of fixed nitrogen is increased by the use of a Linde Molecular Sieve Catalyst.

  11. Regulation of Development and Nitrogen Fixation in Anabaena

    SciTech Connect

    James W Golden

    2004-08-05

    The nitrogen-fixing filamentous cyanobacterium Anabaena sp. strain PCC 7120 is being used as a simple model of microbial development and pattern formation in a multicellular prokaryotic organism. Anabaena reduces atmospheric nitrogen to ammonia in highly specialized, terminally differentiated cells called heterocysts. Anabaena is an important model system because of the multicellular growth pattern, the suspected antiquity of heterocyst development, and the contribution of fixed nitrogen to the environment. We are especially interested in understanding the molecular signaling pathways and genetic regulation that control heterocyst development. In the presence of an external source of reduced nitrogen, the differentiation of heterocysts is inhibited. When Anabaena is grown on dinitrogen, a one-dimensional developmental pattern of single heterocysts separated by approximately ten vegetative cells is established to form a multicellular organism composed of two interdependent cell types. The goal of this project is to understand the signaling and regulatory pathways that commit a vegetative cell to terminally differentiate into a nitrogen-fixing heterocyst. Several genes identified by us and by others were chosen as entry points into the regulatory network. Our research, which was initially focused on transcriptional regulation by group 2 sigma factors, was expanded to include group 3 sigma factors and their regulators after the complete Anabaena genome sequence became available. Surprisingly, no individual sigma factor is essential for heterocyst development. We have used the isolation of extragenic suppressors to study genetic interactions between key regulatory genes such as patS, hetR, and hetC in signaling and developmental pathways. We identified a hetR R223W mutation as a bypass suppressor of patS overexpression. Strains containing the hetR R223W allele fail to respond to pattern formation signals and overexpression of this allele results in a lethal phenotype

  12. Robust biological nitrogen fixation in a model grass-bacterial association.

    PubMed

    Pankievicz, Vânia C S; do Amaral, Fernanda P; Santos, Karina F D N; Agtuca, Beverly; Xu, Youwen; Schueller, Michael J; Arisi, Ana Carolina M; Steffens, Maria B R; de Souza, Emanuel M; Pedrosa, Fábio O; Stacey, Gary; Ferrieri, Richard A

    2015-03-01

    Nitrogen-fixing rhizobacteria can promote plant growth; however, it is controversial whether biological nitrogen fixation (BNF) from associative interaction contributes to growth promotion. The roots of Setaria viridis, a model C4 grass, were effectively colonized by bacterial inoculants resulting in a significant enhancement of growth. Nitrogen-13 tracer studies provided direct evidence for tracer uptake by the host plant and incorporation into protein. Indeed, plants showed robust growth under nitrogen-limiting conditions when inoculated with an ammonium-excreting strain of Azospirillum brasilense. (11)C-labeling experiments showed that patterns in central carbon metabolism and resource allocation exhibited by nitrogen-starved plants were largely reversed by bacterial inoculation, such that they resembled plants grown under nitrogen-sufficient conditions. Adoption of S. viridis as a model should promote research into the mechanisms of associative nitrogen fixation with the ultimate goal of greater adoption of BNF for sustainable crop production. PMID:25645593

  13. Molecular evidence for sediment nitrogen fixation in a temperate New England estuary

    PubMed Central

    Newell, Silvia E.; Pritchard, Kaitlyn R.; Foster, Sarah Q.

    2016-01-01

    Primary production in coastal waters is generally nitrogen (N) limited with denitrification outpacing nitrogen fixation (N2-fixation). However, recent work suggests that we have potentially underestimated the importance of heterotrophic sediment N2-fixation in marine ecosystems. We used clone libraries to examine transcript diversity of nifH (a gene associated with N2-fixation) in sediments at three sites in a temperate New England estuary (Waquoit Bay, Massachusetts, USA) and compared our results to net sediment N2 fluxes previously measured at these sites. We observed nifH expression at all sites, including a site heavily impacted by anthropogenic N. At this N impacted site, we also observed mean net sediment N2-fixation, linking the geochemical rate measurement with nifH expression. This same site also had the lowest diversity (non-parametric Shannon = 2.75). At the two other sites, we also detected nifH transcripts, however, the mean N2 flux indicated net denitrification. These results suggest that N2-fixation and denitrification co-occur in these sediments. Of the unique sequences in this study, 67% were most closely related to uncultured bacteria from various marine environments, 17% to Cluster III, 15% to Cluster I, and only 1% to Cluster II. These data add to the growing body of literature that sediment heterotrophic N2-fixation, even under high inorganic nitrogen concentrations, may be an important yet overlooked source of N in coastal systems. PMID:26977375

  14. A new perspective on environmental controls of marine nitrogen fixation

    NASA Astrophysics Data System (ADS)

    Landolfi, A.; Koeve, W.; Dietze, H.; Kähler, P.; Oschlies, A.

    2015-06-01

    Growing slowly, marine N2 fixers are generally expected to be competitive only where nitrogen (N) supply is low relative to that of phosphorus (P) with respect to the cellular N:P ratio (R) of nonfixing phytoplankton. This is at odds with observed high N2 fixation rates in the oligotrophic North Atlantic where the ratio of nutrients supplied to the surface is elevated in N relative to the average R (16:1). In this study, we investigate several mechanisms to solve this puzzle: iron limitation, phosphorus enhancement by preferential remineralization or stoichiometric diversity of phytoplankton, and dissolved organic phosphorus (DOP) utilization. Combining resource competition theory and a global coupled ecosystem-circulation model, we find that the additional N and energy investments required for exoenzymatic breakdown of DOP give N2 fixers a competitive advantage in oligotrophic P-starved regions. Accounting for this mechanism expands the ecological niche of N2 fixers also to regions where the nutrient supply is high in N relative to R, yielding, in our model, a pattern consistent with the observed high N2 fixation rates in the oligotrophic North Atlantic.

  15. Nitrogen Fixation and Molecular Oxygen: Comparative Genomic Reconstruction of Transcription Regulation in Alphaproteobacteria.

    PubMed

    Tsoy, Olga V; Ravcheev, Dmitry A; Čuklina, Jelena; Gelfand, Mikhail S

    2016-01-01

    Biological nitrogen fixation plays a crucial role in the nitrogen cycle. An ability to fix atmospheric nitrogen, reducing it to ammonium, was described for multiple species of Bacteria and Archaea. The transcriptional regulatory network for nitrogen fixation was extensively studied in several representatives of the class Alphaproteobacteria. This regulatory network includes the activator of nitrogen fixation NifA, working in tandem with the alternative sigma-factor RpoN as well as oxygen-responsive regulatory systems, one-component regulators FnrN/FixK and two-component system FixLJ. Here we used a comparative genomics approach for in silico study of the transcriptional regulatory network in 50 genomes of Alphaproteobacteria. We extended the known regulons and proposed the scenario for the evolution of the nitrogen fixation transcriptional network. The reconstructed network substantially expands the existing knowledge of transcriptional regulation in nitrogen-fixing microorganisms and can be used for genetic experiments, metabolic reconstruction, and evolutionary analysis. PMID:27617010

  16. Nitrogen Fixation and Molecular Oxygen: Comparative Genomic Reconstruction of Transcription Regulation in Alphaproteobacteria

    PubMed Central

    Tsoy, Olga V.; Ravcheev, Dmitry A.; Čuklina, Jelena; Gelfand, Mikhail S.

    2016-01-01

    Biological nitrogen fixation plays a crucial role in the nitrogen cycle. An ability to fix atmospheric nitrogen, reducing it to ammonium, was described for multiple species of Bacteria and Archaea. The transcriptional regulatory network for nitrogen fixation was extensively studied in several representatives of the class Alphaproteobacteria. This regulatory network includes the activator of nitrogen fixation NifA, working in tandem with the alternative sigma-factor RpoN as well as oxygen-responsive regulatory systems, one-component regulators FnrN/FixK and two-component system FixLJ. Here we used a comparative genomics approach for in silico study of the transcriptional regulatory network in 50 genomes of Alphaproteobacteria. We extended the known regulons and proposed the scenario for the evolution of the nitrogen fixation transcriptional network. The reconstructed network substantially expands the existing knowledge of transcriptional regulation in nitrogen-fixing microorganisms and can be used for genetic experiments, metabolic reconstruction, and evolutionary analysis. PMID:27617010

  17. Fixation of nitrogen in the prebiotic atmosphere

    NASA Technical Reports Server (NTRS)

    Yung, Y. L.; Mcelroy, M. B.

    1979-01-01

    Reactions between nitrogen and water in the air surrounding lightning discharges can provide an important source of nitric oxide even under conditions where oxygen is a minor atmospheric constituent. Estimates are given for the associated source of soluble nitrite and nitrate. It is shown that lightning and subsequent atmospheric chemistry can provide a source of nitrate for the primitive ocean as large as one million tons of nitrogen per year, sufficient to fill the ocean to its present level of nitrate in less than one million years.

  18. Heterotrophic organisms dominate nitrogen fixation in the South Pacific Gyre

    PubMed Central

    Halm, Hannah; Lam, Phyllis; Ferdelman, Timothy G; Lavik, Gaute; Dittmar, Thorsten; LaRoche, Julie; D'Hondt, Steven; Kuypers, Marcel MM

    2012-01-01

    Oceanic subtropical gyres are considered biological deserts because of the extremely low availability of nutrients and thus minimum productivities. The major source of nutrient nitrogen in these ecosystems is N2-fixation. The South Pacific Gyre (SPG) is the largest ocean gyre in the world, but measurements of N2-fixation therein, or identification of microorganisms involved, are scarce. In the 2006/2007 austral summer, we investigated nitrogen and carbon assimilation at 11 stations throughout the SPG. In the ultra-oligotrophic waters of the SPG, the chlorophyll maxima reached as deep as 200 m. Surface primary production seemed limited by nitrogen, as dissolved inorganic carbon uptake was stimulated upon additions of 15N-labeled ammonium and leucine in our incubation experiments. N2-fixation was detectable throughout the upper 200 m at most stations, with rates ranging from 0.001 to 0.19 nM N h−1. N2-fixation in the SPG may account for the production of 8–20% of global oceanic new nitrogen. Interestingly, comparable 15N2-fixation rates were measured under light and dark conditions. Meanwhile, phylogenetic analyses for the functional gene biomarker nifH and its transcripts could not detect any common photoautotrophic diazotrophs, such as, Trichodesmium, but a prevalence of γ-proteobacteria and the unicellular photoheterotrophic Group A cyanobacteria. The dominance of these likely heterotrophic diazotrophs was further verified by quantitative PCR. Hence, our combined results show that the ultra-oligotrophic SPG harbors a hitherto unknown heterotrophic diazotrophic community, clearly distinct from other oceanic gyres previously visited. PMID:22170429

  19. Seasonal dynamics of nitrogen fixation and the diazotroph community in the temperate coastal region of the northwestern North Pacific

    NASA Astrophysics Data System (ADS)

    Shiozaki, T.; Nagata, T.; Ijichi, M.; Furuya, K.

    2015-01-01

    Nitrogen fixation in temperate oceans is a potentially important, but poorly understood process that may influence the marine nitrogen budget. This study determined seasonal variations in nitrogen fixation and nifH gene diversity within the euphotic zone in the temperate coastal region of the northwestern North Pacific. Nitrogen fixation as high as 13.6 nmolN L-1 d-1 was measured from early summer to fall when the surface temperature exceeded 14.2 °C and the surface nitrate concentration was low (≤ 0.30 μM), although we also detected nitrogen fixation in subsurface layers (42-62 m) where nitrate concentrations were high (> 1 μM). During periods with high nitrogen fixation, the nifH sequences of UCYN-A were recovered, suggesting that these groups played a key role in nitrogen fixation. The nifH genes were also recovered in spring and winter when nitrogen fixation was undetectable. These genes consisted of many sequences affiliated with Cluster III diazotrophs (putative anaerobic bacteria), which hitherto have rarely been reported to be abundant in surface diazotroph communities in marine environments.

  20. Transcriptional profiling of nitrogen fixation in Azotobacter vinelandii.

    PubMed

    Hamilton, Trinity L; Ludwig, Marcus; Dixon, Ray; Boyd, Eric S; Dos Santos, Patricia C; Setubal, João C; Bryant, Donald A; Dean, Dennis R; Peters, John W

    2011-09-01

    Most biological nitrogen (N(2)) fixation results from the activity of a molybdenum-dependent nitrogenase, a complex iron-sulfur enzyme found associated with a diversity of bacteria and some methanogenic archaea. Azotobacter vinelandii, an obligate aerobe, fixes nitrogen via the oxygen-sensitive Mo nitrogenase but is also able to fix nitrogen through the activities of genetically distinct alternative forms of nitrogenase designated the Vnf and Anf systems when Mo is limiting. The Vnf system appears to replace Mo with V, and the Anf system is thought to contain Fe as the only transition metal within the respective active site metallocofactors. Prior genetic analyses suggest that a number of nif-encoded components are involved in the Vnf and Anf systems. Genome-wide transcription profiling of A. vinelandii cultured under nitrogen-fixing conditions under various metal amendments (e.g., Mo or V) revealed the discrete complement of genes associated with each nitrogenase system and the extent of cross talk between the systems. In addition, changes in transcript levels of genes not directly involved in N(2) fixation provided insight into the integration of central metabolic processes and the oxygen-sensitive process of N(2) fixation in this obligate aerobe. The results underscored significant differences between Mo-dependent and Mo-independent diazotrophic growth that highlight the significant advantages of diazotrophic growth in the presence of Mo. PMID:21724999

  1. Biological nitrogen fixation in non-legume plants

    PubMed Central

    Santi, Carole; Bogusz, Didier; Franche, Claudine

    2013-01-01

    Background Nitrogen is an essential nutrient in plant growth. The ability of a plant to supply all or part of its requirements from biological nitrogen fixation (BNF) thanks to interactions with endosymbiotic, associative and endophytic symbionts, confers a great competitive advantage over non-nitrogen-fixing plants. Scope Because BNF in legumes is well documented, this review focuses on BNF in non-legume plants. Despite the phylogenic and ecological diversity among diazotrophic bacteria and their hosts, tightly regulated communication is always necessary between the microorganisms and the host plant to achieve a successful interaction. Ongoing research efforts to improve knowledge of the molecular mechanisms underlying these original relationships and some common strategies leading to a successful relationship between the nitrogen-fixing microorganisms and their hosts are presented. Conclusions Understanding the molecular mechanism of BNF outside the legume–rhizobium symbiosis could have important agronomic implications and enable the use of N-fertilizers to be reduced or even avoided. Indeed, in the short term, improved understanding could lead to more sustainable exploitation of the biodiversity of nitrogen-fixing organisms and, in the longer term, to the transfer of endosymbiotic nitrogen-fixation capacities to major non-legume crops. PMID:23478942

  2. Nitrogen Fixation (Acetylene Reduction) Associated with Duckweed (Lemnaceae) Mats

    PubMed Central

    Zuberer, D. A.

    1982-01-01

    Duckweed (Lemnaceae) mats in Texas and Florida were investigated, using the acetylene reduction assay, to determine whether nitrogen fixation occurred in these floating aquatic macrophyte communities. N2-fixing microorganisms were enumerated by plating or most-probable-number techniques, using appropriate N-free media. Results of the investigations indicated that substantial N2-fixation (C2H2) was associated with duckweed mats in Texas and Florida. Acetylene reduction values ranged from 1 to 18 μmol of C2H4 g (dry weight)−1 day−1 for samples incubated aerobically in light. Dark N2 fixation was always two- to fivefold lower. 3-(3,4-Dichlorophenyl)-1,1-dimethylurea (7 to 10 μM) reduced acetylene reduction to levels intermediate between light and dark incubation. Acetylene reduction was generally greatest for samples incubated anaerobically in the light. It was estimated that 15 to 20% of the N requirement of the duckweed could be supplied through biological nitrogen fixation. N2-fixing heterotrophic bacteria (105 cells g [wet weight]−1 and cyanobacteria (105 propagules g [wet weight]−1 were associated with the duckweed mats. Azotobacter sp. was not detected in these investigations. One diazotrophic isolate was classified as Klebsiella. PMID:16345992

  3. Physiological limitations and the genetic improvement of symbiotic nitrogen fixation

    SciTech Connect

    Gara, F.O.; Manian, S. ); Drevon, J.J. )

    1988-01-01

    The rhizobium legume symbiosis continues to be of strategic importance particularly in the context of food production. As the world population grows, it is necessary that new developments take place in crop improvement. The development and application of new technologies in biological sciences over past years has made the entire area of plant-microbial interaction an exciting and challenging research area to be involved in. In view of the importance of symbiotic nitrogen fixation, it is not surprising that it still represents one of the priority areas for commercial development in agricultural biotechnology. Since this symbiosis involves an association between procaryotic and eucaryhotic partners, it requires of necessity a coordinated and interdisciplinary approach. This book focuses on physiological limitations affecting symbiotic nitrogen fixation and the potential for overcoming such limitations by using genetic technologies.

  4. Enhanced symbiotic nitrogen fixation with P. syringae pv tabaci

    SciTech Connect

    Langston-Unkefer, P.J.; Knight, T.J. New Mexico State Univ., Las Cruces ); Sengupta-Gopalan, C. )

    1989-04-01

    Infestation of legumes such as alfalfa and soybeans with the plant pathogen Pseudomonas syringae pv. tabaci is accompanied by increased plant growth, nodulation, overall nitrogen fixation, and total assimilated nitrogen. These effects are observed only in plants infested with Tox{sup +} pathogen; the toxin is tabtoxinine-{beta}-lactam, an active site-directed irreversible inhibitor of glutamine synthetase. The key to the legumes survival of this treatment is the insensitivity of the nodule-specific form of glutamine synthetase to the toxin. As expected, significant changes are observed in ammonia assimilation in these plants. The biochemical and molecular biological consequences of this treatment are being investigated.

  5. The sensitivity of marine N2 fixation to dissolved inorganic nitrogen

    PubMed Central

    Knapp, Angela N.

    2012-01-01

    The dominant process adding nitrogen (N) to the ocean, di-nitrogen (N2) fixation, is mediated by prokaryotes (diazotrophs) sensitive to a variety of environmental factors. In particular, it is often assumed that consequential rates of marine N2 fixation do not occur where concentrations of nitrate (NO−3) and/or ammonium (NH+4) exceed 1μM because of the additional energetic cost associated with assimilating N2 gas relative to NO−3 or NH+4. However, an examination of culturing studies and in situ N2 fixation rate measurements from marine euphotic, mesopelagic, and benthic environments indicates that while elevated concentrations of NO−3 and/or NH+4 can depress N2 fixation rates, the process can continue at substantial rates in the presence of as much as 30μM NO−3 and/or 200μM NH+4. These findings challenge expectations of the degree to which inorganic N inhibits this process. The high rates of N2 fixation measured in some benthic environments suggest that certain benthic diazotrophs may be less sensitive to prolonged exposure to NO−3 and/or NH+4 than cyanobacterial diazotrophs. Additionally, recent work indicates that cyanobacterial diazotrophs may have mechanisms for mitigating NO−3 inhibition of N2 fixation. In particular, it has been recently shown that increasing phosphorus (P) availability increases diazotroph abundance, thus compensating for lower per-cell rates of N2 fixation that result from NO−3 inhibition. Consequently, low ambient surface ocean N:P ratios such as those generated by the increasing rates of N loss thought to occur during the last glacial to interglacial transition may create conditions favorable for N2 fixation and thus help to stabilize the marine N inventory on relevant time scales. These findings suggest that restricting measurements of marine N2 fixation to oligotrophic surface waters may underestimate global rates of this process and contribute to uncertainties in the marine N budget. PMID:23091472

  6. Improvement in nitrogen fixation capacity could be part of the domestication process in soybean.

    PubMed

    Muñoz, N; Qi, X; Li, M-W; Xie, M; Gao, Y; Cheung, M-Y; Wong, F-L; Lam, H-M

    2016-08-01

    Biological nitrogen fixation (BNF) in soybeans is a complex process involving the interplay between the plant host and the symbiotic rhizobia. As nitrogen supply has a crucial role in growth and development, higher nitrogen fixation capacity would be important to achieve bigger plants and larger seeds, which were important selection criteria during plant domestication by humans. To test this hypothesis, we monitored the nitrogen fixation-related performance in 31 cultivated and 17 wild soybeans after inoculation with the slow-growing Bradyrhizobium diazoefficiens sp. nov. USDA110 and the fast-growing Sinorhizobium (Ensifer) fredii CCBAU45436. Our results showed that, in general, cultivated soybeans gave better performance in BNF. Electron microscopic studies indicated that there was an exceptionally high accumulation of poly-β-hydroxybutyrate bodies in bacteroids in the nodules of all wild soybeans tested, suggesting that the C/N balance in wild soybeans may not be optimized for nitrogen fixation. Furthermore, we identified new quantitative trait loci (QTLs) for total ureides and total nodule fresh weight by employing a recombinant inbred population composed of descendants from a cross between a cultivated and a wild parent. Using nucleotide diversity (θπ), divergence index (Fst) and distribution of fixed single-nucleotide polymorphisms as parameters, we found that some regions in the total ureides QTL on chromosome 17 and the total nodule fresh weight QTL on chromosome 12 exhibited very low diversity among cultivated soybeans, suggesting that these were traits specially selected during the domestication and breeding process. PMID:27118154

  7. EFFECT OF NITROGEN AND METAL ADDITIONS ON NITROGEN FIXATION ACTIVITY IN BIOLOGICAL SOIL CRUSTS

    NASA Astrophysics Data System (ADS)

    Alexander, K.; Lui, D.; Anbar, A. D.; Garcia-Pichel, F.; Hartnett, H. E.

    2009-12-01

    Biological soil crusts (BSCs) are diverse consortia of microorganisms that live in intimate association with soils in arid environments. Also called cryptogamic or microbiotic crusts, these communities can include cyanobacteria, algae, heterotrophic bacteria, fungi, lichens, and mosses. Together, these organisms provide many services to their surrounding ecosystems, including reduction of water runoff, promotion of water infiltration, and prevention of soil erosion. The cyanobacteria and algae also provide fixed carbon (C) to the soil through photosynthesis, and because atmospheric deposition of nitrogen (N) in arid environments is low, the major input of biologically available N comes from cyanobacteria capable of converting nitrogen gas (N2) to ammonium (NH4+). Biological soil crusts are easily destroyed by livestock grazing, motor vehicle travel, and many forms of recreational and agricultural land use. Loss of BSC cover can leave the soil vulnerable to intense erosion that can remove the nutrients necessary to sustain plant and animal life, thus accelerating the process of desertification. In order to preserve existing crusts and encourage the development of new crusts, it is crucial to understand the nutrient requirements of metabolism and growth in these microbial communities. This study investigated the affect of nitrogen and metal additions on N2-fixation activity in cyanobacterially-dominated crusts from the Colorado Plateau near Moab, Utah. Although N2-fixation has been studied in this system before, the affect of nutrient additions on N2-fixation activity has not been documented. The goal of this work was to understand how N and metal supplementation affects crust N metabolism. Three experiments were conducted to observe how N2-fixation activity changed with the addition of N, molybdenum (Mo), and vanadium (V). Molybdenum and vanadium were chosen because they are most commonly found at the active site of the enzyme nitrogenase, the molecule responsible

  8. Nitrogen fixation rates in algal turf communities of a degraded versus less degraded coral reef

    NASA Astrophysics Data System (ADS)

    den Haan, Joost; Visser, Petra M.; Ganase, Anjani E.; Gooren, Elfi E.; Stal, Lucas J.; van Duyl, Fleur C.; Vermeij, Mark J. A.; Huisman, Jef

    2014-12-01

    Algal turf communities are ubiquitous on coral reefs in the Caribbean and are often dominated by N2-fixing cyanobacteria. However, it is largely unknown (1) how much N2 is actually fixed by turf communities and (2) which factors affect their N2 fixation rates. Therefore, we compared N2 fixation activity by turf communities at different depths and during day and night-time on a degraded versus a less degraded coral reef site on the island of Curaçao. N2 fixation rates measured with the acetylene reduction assay were slightly higher in shallow (5-10-m depth) than in deep turf communities (30-m depth), and N2 fixation rates during the daytime significantly exceeded those during the night. N2 fixation rates by the turf communities did not differ between the degraded and less degraded reef. Both our study and a literature survey of earlier studies indicated that turf communities tend to have lower N2 fixation rates than cyanobacterial mats. However, at least in our study area, turf communities were more abundant than cyanobacterial mats. Our results therefore suggest that turf communities play an important role in the nitrogen cycle of coral reefs. N2 fixation by turfs may contribute to an undesirable positive feedback that promotes the proliferation of algal turf communities while accelerating coral reef degradation.

  9. Genome-wide association analysis of symbiotic nitrogen fixation in common bean

    Technology Transfer Automated Retrieval System (TEKTRAN)

    A genome-wide association study (GWAS) was conducted to explore the genetic basis of variation for symbiotic nitrogen fixation (SNF) and related traits in the Andean diversity panel (ADP) comprised of 259 common bean (Phaseolus vulgaris) genotypes. The ADP was evaluated for SNF and related traits in...

  10. Nitrogen Fixation Tolerance to Soil Water Deficit Among Commercial Cultivars and breeding Lines of Peanut

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Peanut is often grown in the U.S. on sandy soil with limited water holding capacity. Since nitrogen fixation activity of other grain legume species, and some peanut cultivars, has been found to be especially sensitive to soil drying, this study was undertaken to examine a possible limitation in U.S...

  11. Methane-Stimulated Benthic Marine Nitrogen Fixation at Deep-Sea Methane Seeps

    NASA Astrophysics Data System (ADS)

    Dekas, A. E.; Orphan, V.

    2011-12-01

    Biological nitrogen fixation (the conversion of N2 to NH3) is a critical process in the oceans, counteracting the production of N2 gas by dissimilatory bacterial metabolisms and providing a source of bioavailable nitrogen to many nitrogen-limited ecosystems. Although current measurements of N2 production and consumption in the oceans indicate that the nitrogen cycle is not balanced, recent findings on the limits of nitrogen fixation suggest that the perceived imbalance is an artifact of an incomplete assessment of marine diazotrophy. One currently poorly studied and potentially underappreciated habitat for diazotrophic organisms is the sediments of the deep-sea. In the present study we investigate the distribution and magnitude of benthic marine diazotrophy at several active deep-sea methane seeps (Mound 12, Costa Rica; Eel River Basin, CA, USA; Hydrate Ridge, OR, USA; and Monterey Canyon, CA, USA). Using 15N2 and 15NH4 sediment incubation experiments followed by single-cell (FISH-NanoSIMS) and bulk isotopic analysis (EA-IRMS), we observed total protein synthesis (15N uptake from 15NH4) and nitrogen fixation (15N update from 15N2). The highest rates of nitrogen fixation observed in the methane seep sediment incubation experiments were over an order of magnitude greater than those previously published from non-seep deep-sea sediments (Hartwig and Stanley, Deep-Sea Research, 1978, 25:411-417). However, methane seep diazotrophy appears to be highly spatially variable, with sediments exhibiting no nitrogen fixation originating only centimeters away from sediments actively incorporating 15N from 15N2. The greatest spatial variability in diazotrophy was observed with depth in the sediment, and corresponded to steep gradients in sulfate and methane. The maximum rates of nitrogen fixation were observed within the methane-sulfate transition zone, where organisms mediating the anaerobic oxidation of methane are typically in high abundance. Additionally, incubation

  12. Fixating on metals: new insights into the role of metals in nodulation and symbiotic nitrogen fixation

    PubMed Central

    González-Guerrero, Manuel; Matthiadis, Anna; Sáez, Áez;ngela; Long, Terri A.

    2014-01-01

    Symbiotic nitrogen fixation is one of the most promising and immediate alternatives to the overuse of polluting nitrogen fertilizers for improving plant nutrition. At the core of this process are a number of metalloproteins that catalyze and provide energy for the conversion of atmospheric nitrogen to ammonia, eliminate free radicals produced by this process, and create the microaerobic conditions required by these reactions. In legumes, metal cofactors are provided to endosymbiotic rhizobia within root nodule cortical cells. However, low metal bioavailability is prevalent in most soils types, resulting in widespread plant metal deficiency and decreased nitrogen fixation capabilities. As a result, renewed efforts have been undertaken to identify the mechanisms governing metal delivery from soil to the rhizobia, and to determine how metals are used in the nodule and how they are recycled once the nodule is no longer functional. This effort is being aided by improved legume molecular biology tools (genome projects, mutant collections, and transformation methods), in addition to state-of-the-art metal visualization systems. PMID:24592271

  13. Screening Prosopis (mesquite) germplasm for biomass production and nitrogen fixation

    SciTech Connect

    Felker, P.; Cannell, G.H.; Clark, P.R.; Osborn, J.F.

    1980-01-01

    The nitrogen-fixing trees of the genus Prosopis (mesquite or algaroba) are well adapted to the semi-arid and often saline regions of the world. These trees may produce firewood or pods for livestock food, they may stabilize sand dunes and they may enrich the soil by production of leaf litter supported by nitrogen fixation. A collection of nearly 500 Prosopis accessions representing North and South American and African germplasm has been established. Seventy of these accessions representing 14 taxa are being grown under field conditions where a 30-fold range in biomass productivity among accessions has been estimated. In a greehouse experiment, 13 Prosopis taxa grew on nitrogen-free medium nodulated, and had a 10-fold difference in nitrogen fixation (acetylene reduction). When Prosopis is propagated by seed the resulting trees are extremely variable in growth rate and presence or absence of thorns. Propagation of 6 Prosopis taxa by stem cuttings has been achieved with low success (1 to 10%) in field-grown plants and with higher success (50 to 100%) with young actively growing greenhouse plants.

  14. Can we trust current estimates for biological nitrogen fixation?

    NASA Astrophysics Data System (ADS)

    Bellenger, Jean-Philippe; Kraepiel, Anne

    2016-04-01

    Biological nitrogen fixation (BNF) consists on the reduction of atmospheric dinitrogen (N2) into bioavailable ammonium. This reaction accounts for up to 97% of nitrogen (N) input in unmanaged terrestrial ecosystems. Closing the N budget is a long standing challenge in many ecosystems. Recent studies have highlighted that current methods used to assess BNF are affected by critical biases. These findings challenge our confidence in many N budgets and call for a profound reconsideration of our methodological approaches. Beside these methodological issues, our ability to properly assess BNF might be further altered as a result of a misconception regarding the importance of BNF enzymatic diversity in nature. BNF is catalyzed by the enzyme nitrogenase (Nase) for which three isoforms have been identified so far; the molybdenum (Mo), vanadium (V) and iron-only (Fe) isoforms. Currently BNF is mostly considered to primarily depend on the Mo isoform. The contribution of the alternative Nases (V and Fe isoforms) to BNF in natural habitats has been mostly overlooked. However, recent findings have challenged this traditional view of the Nases hierarchy (Mo isoform predominance) with deep implications for BNF assessment in the field. Here, I will present an overview of recent findings, provided by various research groups, challenging current methods used to assess BNF. I will also present a summary of recent studies highlighting the importance of alternative Nases in nature. I will finally illustrate how altering our view on the Mo-Nase predominance can deeply affect our confidence in current BNF estimates. I will conclude by presenting new methodological approaches that will contribute to significantly improve our ability to understand and estimate BNF in the field by improving our capacity to access BNF spatio-temporal variability and enzymatic diversity.

  15. Functional ecology of free-living nitrogen fixation: A contemporary perspective

    USGS Publications Warehouse

    Reed, Sasha C.; Cleveland, Cory C.; Townsend, Alan R.

    2011-01-01

    Nitrogen (N) availability is thought to frequently limit terrestrial ecosystem processes, and explicit consideration of N biogeochemistry, including biological N2 fixation, is central to understanding ecosystem responses to environmental change. Yet, the importance of free-living N2 fixation—a process that occurs on a wide variety of substrates, is nearly ubiquitous in terrestrial ecosystems, and may often represent the dominant pathway for acquiring newly available N—is often underappreciated. Here, we draw from studies that investigate free-living N2 fixation from functional, physiological, genetic, and ecological perspectives. We show that recent research and analytical advances have generated a wealth of new information that provides novel insight into the ecology of N2 fixation as well as raises new questions and priorities for future work. These priorities include a need to better integrate free-living N2 fixation into conceptual and analytical evaluations of the N cycle's role in a variety of global change scenarios.

  16. Engineering Pseudomonas protegens Pf-5 for Nitrogen Fixation and its Application to Improve Plant Growth under Nitrogen-Deficient Conditions

    PubMed Central

    Setten, Lorena; Soto, Gabriela; Mozzicafreddo, Matteo; Fox, Ana Romina; Lisi, Christian; Cuccioloni, Massimiliano; Angeletti, Mauro; Pagano, Elba; Díaz-Paleo, Antonio; Ayub, Nicolás Daniel

    2013-01-01

    Nitrogen is the second most critical factor for crop production after water. In this study, the beneficial rhizobacterium Pseudomonas protegens Pf-5 was genetically modified to fix nitrogen using the genes encoding the nitrogenase of Pseudomonas stutzeri A1501 via the X940 cosmid. Pf-5 X940 was able to grow in L medium without nitrogen, displayed high nitrogenase activity and released significant quantities of ammonium to the medium. Pf-5 X940 also showed constitutive expression and enzymatic activity of nitrogenase in ammonium medium or in nitrogen-free medium, suggesting a constitutive nitrogen fixation. Similar to Pseudomonas protegens Pf-5, Pseudomonas putida, Pseudomonas veronii and Pseudomonas taetrolens but not Pseudomonas balearica and Pseudomonas stutzeri transformed with cosmid X940 showed constitutive nitrogenase activity and high ammonium production, suggesting that this phenotype depends on the genome context and that this technology to obtain nitrogen-fixing bacteria is not restricted to Pf-5. Interestingly, inoculation of Arabidopsis, alfalfa, tall fescue and maize with Pf-5 X940 increased the ammonium concentration in soil and plant productivity under nitrogen-deficient conditions. In conclusion, these results open the way to the production of effective recombinant inoculants for nitrogen fixation on a wide range of crops. PMID:23675499

  17. Nitrogen Fixation on Early Mars and Other Terrestrial Planets: Experimental Demonstration of Abiotic Fixation Reactions to Nitrite and Nitrate

    NASA Astrophysics Data System (ADS)

    Summers, David P.; Khare, Bishun

    2007-05-01

    Understanding the abiotic fixation of nitrogen is critical to understanding planetary evolution and the potential origin of life on terrestrial planets. Nitrogen, an essential biochemical element, is certainly necessary for life as we know it to arise. The loss of atmospheric nitrogen can result in an incapacity to sustain liquid water and impact planetary habitability and hydrological processes that shape the surface. However, our current understanding of how such fixation may occur is almost entirely theoretical. This work experimentally examines the chemistry, in both gas and aqueous phases, that would occur from the formation of NO and CO by the shock heating of a model carbon dioxide/nitrogen atmosphere such as is currently thought to exist on early terrestrial planets. The results show that two pathways exist for the abiotic fixation of nitrogen from the atmosphere into the crust: one via HNO and another via NO2. Fixation via HNO, which requires liquid water, could represent fixation on a planet with liquid water (and hence would also be a source of nitrogen for the origin of life). The pathway via NO2 does not require liquid water and shows that fixation could occur even when liquid water has been lost from a planet's surface (for example, continuing to remove nitrogen through NO2 reaction with ice, adsorbed water, etc.).

  18. Nitrogen fixation in distinct microbial niches within a chemoautotrophy-driven cave ecosystem

    PubMed Central

    Desai, Mahesh S; Assig, Karoline; Dattagupta, Sharmishtha

    2013-01-01

    Microbial sulfur and carbon cycles in ecosystems driven by chemoautotrophy—present at deep-sea hydrothermal vents, cold seeps and sulfidic caves—have been studied to some extent, yet little is known about nitrogen fixation in these systems. Using a comprehensive approach comprising of 15N2 isotope labeling, acetylene reduction assay and nitrogenase gene expression analyses, we investigated nitrogen fixation in the sulfide-rich, chemoautotrophy-based Frasassi cave ecosystem (Italy). Nitrogen fixation was examined in three different microbial niches within the cave waters: (1) symbiotic bacterial community of Niphargus amphipods, (2) Beggiatoa-dominated biofilms, which occur at the sulfide–oxygen interface, and (3) sulfidic sediment. We found evidence for nitrogen fixation in all the three niches, and the nitrogenase gene (homologs of nifH) expression data clearly show niche differentiation of diazotrophic Proteobacteria within the water streams. The nifH transcript originated from the symbiotic community of Niphargus amphipods might belong to the Thiothrix ectosymbionts. Two abundantly expressed nifH genes in the Beggiatoa-dominated biofilms are closely related to those from Beggiatoa- and Desulfovibrio-related bacteria. These two diazotrophs were consistently found in Beggiatoa-dominated biofilms collected at various time points, thus illustrating species-specific associations of the diazotrophs in biofilm formation, and micron-scale niche partitioning of sulfur-oxidizing and sulfate-reducing bacteria driven by steep redox gradients within the biofilm. Finally, putative heterotrophs (Geobacter, Azoarcus and Desulfovibrio related) were the active diazotrophs in the sulfidic sediment. Our study is the first to shed light on nitrogen fixation in permanently dark caves and suggests that diazotrophy may be widespread in chemosynthetic communities. PMID:23924780

  19. Nitrogen fixation in distinct microbial niches within a chemoautotrophy-driven cave ecosystem.

    PubMed

    Desai, Mahesh S; Assig, Karoline; Dattagupta, Sharmishtha

    2013-12-01

    Microbial sulfur and carbon cycles in ecosystems driven by chemoautotrophy-present at deep-sea hydrothermal vents, cold seeps and sulfidic caves-have been studied to some extent, yet little is known about nitrogen fixation in these systems. Using a comprehensive approach comprising of (15)N2 isotope labeling, acetylene reduction assay and nitrogenase gene expression analyses, we investigated nitrogen fixation in the sulfide-rich, chemoautotrophy-based Frasassi cave ecosystem (Italy). Nitrogen fixation was examined in three different microbial niches within the cave waters: (1) symbiotic bacterial community of Niphargus amphipods, (2) Beggiatoa-dominated biofilms, which occur at the sulfide-oxygen interface, and (3) sulfidic sediment. We found evidence for nitrogen fixation in all the three niches, and the nitrogenase gene (homologs of nifH) expression data clearly show niche differentiation of diazotrophic Proteobacteria within the water streams. The nifH transcript originated from the symbiotic community of Niphargus amphipods might belong to the Thiothrix ectosymbionts. Two abundantly expressed nifH genes in the Beggiatoa-dominated biofilms are closely related to those from Beggiatoa- and Desulfovibrio-related bacteria. These two diazotrophs were consistently found in Beggiatoa-dominated biofilms collected at various time points, thus illustrating species-specific associations of the diazotrophs in biofilm formation, and micron-scale niche partitioning of sulfur-oxidizing and sulfate-reducing bacteria driven by steep redox gradients within the biofilm. Finally, putative heterotrophs (Geobacter, Azoarcus and Desulfovibrio related) were the active diazotrophs in the sulfidic sediment. Our study is the first to shed light on nitrogen fixation in permanently dark caves and suggests that diazotrophy may be widespread in chemosynthetic communities. PMID:23924780

  20. Nitrogen fixation method and apparatus. [DOE patent application

    SciTech Connect

    Chen, H.L.

    1981-08-11

    A method and apparatus for achieving nitrogen fixation includes a volumetric electric discharge chamber. The volumetric discharge chamber provides an even distribution of an electron beam, and enables the chamber to be maintained at a controlled energy to pressure (E/p) ratio. An E/p ratio of from 5 to 15 kV/atm of O/sub 2//cm promotes the formation of vibrationally excited N/sub 2/. Atomic oxygen interacts with vibrationally excited N/sub 2/ at a much quicker rate than unexcited N/sub 2/, greatly improving the rate at which NO is formed.

  1. Assessment of free-living nitrogen fixing microorganisms for commercial nitrogen fixation. [economic analysis of ammonia production

    NASA Technical Reports Server (NTRS)

    Stokes, B. O.; Wallace, C. J.

    1978-01-01

    Ammonia production by Klebsiella pneumoniae is not economical with present strains and improving nitrogen fixation to its theoretical limits in this organism is not sufficient to achieve economic viability. Because the value of both the hydrogen produced by this organism and the methane value of the carbon source required greatly exceed the value of the ammonia formed, ammonia (fixed nitrogen) should be considered the by-product. The production of hydrogen by KLEBSIELLA or other anaerobic nitrogen fixers should receive additional study, because the activity of nitrogenase offers a significant improvement in hydrogen production. The production of fixed nitrogen in the form of cell mass by Azotobacter is also uneconomical and the methane value of the carbon substrate exceeds the value of the nitrogen fixed. Parametric studies indicate that as efficiencies approach the theoretical limits the economics may become competitive. The use of nif-derepressed microorganisms, particularly blue-green algae, may have significant potential for in situ fertilization in the environment.

  2. Nitrogen fixation by Trichodesmium spp. and unicellular diazotrophs in the North Pacific Subtropical Gyre

    NASA Astrophysics Data System (ADS)

    Sohm, Jill A.; Subramaniam, Ajit; Gunderson, Troy E.; Carpenter, Edward J.; Capone, Douglas G.

    2011-09-01

    Nitrogen (N2) fixation is an important process that fuels export production in the North Pacific Ocean, as evidenced by seasonally low δ15N of sinking organic nitrogen (N) at the Hawaii Ocean Time series station. However, relatively few direct measurements of N2 fixation exist across the North Pacific. On two cruises there in fall 2002 and summer 2003, the abundance and N2 fixation rate of Trichodesmium spp. and Richelia, as well as bulk water samples, were measured. Trichodesmium spp. were only detected in the area near the Hawaiian Islands, in similar densities on both cruises. Despite similar densities, the areal N2 fixation rate of Trichodesmium spp. in fall 2002 was nearly four times greater than in summer 2003 at stations proximal to the Hawaiian Islands. In the central North Pacific Gyre far from the Hawaiian Islands, where Trichodesmium spp. was not present, whole water N2 fixation rates were relatively high (˜100 μmol N m-2 d-1). Presumably unicellular diazotrophs were responsible for activity there. Our studies show a geographical variation in the dominant diazotroph in the North Pacific Subtropical Gyre in the summer with Trichodesmium being dominant around the Hawaiian Islands, Richelia associated with diatoms to be found in high numbers to the south of the islands while unicellular diazotrophs dominated to the west, away from the islands and evidence from the literature suggests iron may play a role.

  3. Nitrogen fixation in boreal peatlands: the effects of increased N deposition on N2-fixation

    NASA Astrophysics Data System (ADS)

    Popma, J. M.; Wieder, R.; Lamers, L.; Vile, M. A.

    2013-12-01

    Boreal peatlands are of great importance to global carbon and nitrogen cycling. While covering only 3-4 % of the terrestrial surface, they account for 25-30 % of the world's soil C and 9-15 % of the world's soil N. In Western Canada atmospheric dry deposition rates are extremely low: approximately 1 kg N ha-1 yr-1. Though these systems have been functioning as net sinks over the past 11,000 years, natural and anthropogenic disturbances might compromise the historical balance of C and N. Biological N2-fixation has recently been shown to represent a very significant input of N into these systems, contributing to 62% of total N in Western Canada. Interactions between N deposition and biological N2-fixation are as yet, unknown, but the impact of elevated deposition of N-compounds from increased industrial expansion of oil sands mining to peatlands, is concerning. Given that nitrogenase, the enzyme responsible for catalyzing N2-fixation, is energetically costly when active, enhanced inputs of atmospheric N deposition could be a major determinant for enzyme activity and rates of biological N input to these bogs. Understanding interactions between N deposition and N2 fixation in boreal peatlands can aid in predicting the consequences of increased N deposition and setting critical loads. We conducted a field-fertilization experiment in a poor fen in Alberta, Canada, to determine the effects of enhanced N deposition on a dominant fen species Sphagnum angustifolium. The experiment consisted of seven N treatments: Control, 0, 5, 10, 15, 20 and 25 kg N ha-1 y1, n=3. N2-fixation was measured during summer 2012 and 2013 using the acetylene reduction assay (ARA). ARA rates were converted to rates of N2-fixation by calibrating ARA with paired 15N2-incubations. In both 2012 and 2013, with increasing N deposition from 0 kg N ha-1 yr-1 to 25 kg N ha-1 yr-1, rates of N2 fixation decreased, with highest rates in the 0 kg N ha-1 yr-1 treatment mosses (54.2 × 1.40; 48.58 × 7.12 kg N ha

  4. Orbital Variation in South China Sea Nitrogen Fixation over the Past 420,000 yrs

    NASA Astrophysics Data System (ADS)

    Ren, H. A.; Sigman, D. M.; Anderson, R. F.; Martinez-Garcia, A.; Chen, M.; Straub, M.; Haug, G. H.

    2012-12-01

    Previous records of planktonic foraminifera shell-bound nitrogen isotopes (FB-δ15N) in the Caribbean Sea and the South China Sea (SCS) both indicate lower nitrogen fixation during the last glacial maximum than the current interglacial and have been explained as a N fixation response to the supply of excess phosphorus ultimately arising from denitrification. In this study, we extended the FB-δ15N record in the SCS (MD97-2142) back to 420 ka. The extended SCS record confirms previous findings that the N fixation rate was higher during interglacials. The full glacial/interglacial amplitude of the SCS N fixation change is similar to that observed in the Caribbean. At all 5 glacial terminations, an increase in N fixation in the SCS coincides with the G. ruber δ18Oc decrease, sea level rise, and the deglacial increase in water column denitrification in the eastern tropical North Pacific, although the SCS FB-δ15N decrease appears to be slower than the δ18O decrease in the two most recent terminations. More broadly, SCS FB-δ15N and δ18Oc are similar in large scale structure and together imply a strong connection of SCS N fixation to sea level. This is arguably to be expected, as the extensive continental shelf area adjacent to the southern SCS appears to be a global hotspot for benthic denitrification during interglacials, while this shelf area would have been nearly completely lost during peak ice ages. For the interglacials in which there is a clear precession cycle in SCS FB-δ15N, δ15N minima lag δ18Oc minima by about 5-7 kyrs at the precession band. This suggests that the N fixation maxima are roughly anti-phased with water column denitrification, which peaks during northern hemisphere warm phases. On the precession time scale, maxima in N fixation rate (minima in FB-δ15N) coincide with stronger upwelling and shallower thermocline depth as indicated by changes in planktonic foraminifera species abundance at the same site. We infer that periods of lower

  5. Photosynthate partitioning and nitrogen fixation of alfalfa and birdsfoot trefoil. [Lotus corniculatus L. ; Medicago sativa L

    SciTech Connect

    Shieh, W.J.

    1985-01-01

    Nodule mass and number are usually correlated with rates of nitrogen fixation in legumes. Birdsfoot trefoil (Lotus corniculatus L.) with more than twice the nodule number and mass, however, fixes far less nitrogen than alfalfa (Medicago sativa L.) at the same age. In this research, photosynthesis and photosynthate partitioning and utilization in relation to nitrogen fixation of alfalfa and birdsfoot trefoil were examined in order to determine their relationship to nitrogen fixation potential. Photosynthate to nodules was studied using /sup 14/CO/sub 2/ labeling techniques. Partitioning patterns were altered by shading and dark depletion treatments. Efficiency of photosynthate utilization was examined by determining turnover of /sup 14/C photosynthate in nodule metabolites and by studying rates of cyanide-resistant and cyanide-sensitive O/sub 2/ uptake. Alfalfa nodule activity was greater than trefoil expressed on a hole pot or nodule dry weight basis. Both shading and dark treatments significantly reduced nodule activity as estimated by the acetylene reduction assay. Shoots of both species were found to be the dominant sinks for photosynthate. Percentage /sup 14/C recovered in alfalfa roots was more than twice that of trefoil at 1,2,3,4 and 24 h after labeling. Greater relative specific radioactivity (RSA) in nodules of both species suggests that they were stronger sinks for current photosynthate than roots.

  6. Nitrogen fixation rate and chlorophyll content of the lichen Peltigera canina exposed to sulfur dioxide

    SciTech Connect

    Henriksson, E.; Pearson, L.C.

    1981-01-01

    In general, the rate of nitrogen fixation decreased when the lichen Peltigera canina (L.) Willd. was exposed to sulfur dioxide gas at levels from 0.1 to 500 ppm; at 30 ppm, however, nitrogen fixation was stimulated. The chlorophyll content decreased as the level of sulfur dioxide increased.

  7. Distribution of nitrogen fixation and nitrogenase-like sequences amongst microbial genomes

    PubMed Central

    2012-01-01

    Background The metabolic capacity for nitrogen fixation is known to be present in several prokaryotic species scattered across taxonomic groups. Experimental detection of nitrogen fixation in microbes requires species-specific conditions, making it difficult to obtain a comprehensive census of this trait. The recent and rapid increase in the availability of microbial genome sequences affords novel opportunities to re-examine the occurrence and distribution of nitrogen fixation genes. The current practice for computational prediction of nitrogen fixation is to use the presence of the nifH and/or nifD genes. Results Based on a careful comparison of the repertoire of nitrogen fixation genes in known diazotroph species we propose a new criterion for computational prediction of nitrogen fixation: the presence of a minimum set of six genes coding for structural and biosynthetic components, namely NifHDK and NifENB. Using this criterion, we conducted a comprehensive search in fully sequenced genomes and identified 149 diazotrophic species, including 82 known diazotrophs and 67 species not known to fix nitrogen. The taxonomic distribution of nitrogen fixation in Archaea was limited to the Euryarchaeota phylum; within the Bacteria domain we predict that nitrogen fixation occurs in 13 different phyla. Of these, seven phyla had not hitherto been known to contain species capable of nitrogen fixation. Our analyses also identified protein sequences that are similar to nitrogenase in organisms that do not meet the minimum-gene-set criteria. The existence of nitrogenase-like proteins lacking conserved co-factor ligands in both diazotrophs and non-diazotrophs suggests their potential for performing other, as yet unidentified, metabolic functions. Conclusions Our predictions expand the known phylogenetic diversity of nitrogen fixation, and suggest that this trait may be much more common in nature than it is currently thought. The diverse phylogenetic distribution of nitrogenase

  8. The Sensitivity of Moss-Associated Nitrogen Fixation towards Repeated Nitrogen Input

    PubMed Central

    Rousk, Kathrin; Michelsen, Anders

    2016-01-01

    Nitrogen (N2) fixation is a major source of available N in ecosystems that receive low amounts of atmospheric N deposition. In boreal forest and subarctic tundra, the feather moss Hylocomium splendens is colonized by N2 fixing cyanobacteria that could contribute fundamentally to increase the N pool in these ecosystems. However, N2 fixation in mosses is inhibited by N input. Although this has been shown previously, the ability of N2 fixation to grow less sensitive towards repeated, increased N inputs remains unknown. Here, we tested if N2 fixation in H. splendens can recover from increased N input depending on the N load (0, 5, 20, 80, 320 kg N ha-1 yr-1) after a period of N deprivation, and if sensitivity towards increased N input can decrease after repeated N additions. Nitrogen fixation in the moss was inhibited by the highest N addition, but was promoted by adding 5 kg N ha-1 yr-1, and increased in all treatments during a short period of N deprivation. The sensitivity of N2 fixation towards repeated N additions seem to decrease in the 20 and 80 kg N additions, but increased in the highest N addition (320 kg N ha-1 yr-1). Recovery of N in leachate samples increased with increasing N loads, suggesting low retention capabilities of mosses if N input is above 5 kg N ha-1 yr-1. Our results demonstrate that the sensitivity towards repeated N additions is likely to decrease if N input does not exceed a certain threshold. PMID:26731691

  9. The Sensitivity of Moss-Associated Nitrogen Fixation towards Repeated Nitrogen Input.

    PubMed

    Rousk, Kathrin; Michelsen, Anders

    2016-01-01

    Nitrogen (N2) fixation is a major source of available N in ecosystems that receive low amounts of atmospheric N deposition. In boreal forest and subarctic tundra, the feather moss Hylocomium splendens is colonized by N2 fixing cyanobacteria that could contribute fundamentally to increase the N pool in these ecosystems. However, N2 fixation in mosses is inhibited by N input. Although this has been shown previously, the ability of N2 fixation to grow less sensitive towards repeated, increased N inputs remains unknown. Here, we tested if N2 fixation in H. splendens can recover from increased N input depending on the N load (0, 5, 20, 80, 320 kg N ha(-1) yr(-1)) after a period of N deprivation, and if sensitivity towards increased N input can decrease after repeated N additions. Nitrogen fixation in the moss was inhibited by the highest N addition, but was promoted by adding 5 kg N ha(-1) yr(-1), and increased in all treatments during a short period of N deprivation. The sensitivity of N2 fixation towards repeated N additions seem to decrease in the 20 and 80 kg N additions, but increased in the highest N addition (320 kg N ha(-1) yr(-1)). Recovery of N in leachate samples increased with increasing N loads, suggesting low retention capabilities of mosses if N input is above 5 kg N ha(-1) yr(-1). Our results demonstrate that the sensitivity towards repeated N additions is likely to decrease if N input does not exceed a certain threshold. PMID:26731691

  10. Climatic and Grazing Controls on Biological Soil Crust Nitrogen Fixation in Semi-arid Ecosystems

    NASA Astrophysics Data System (ADS)

    Schwabedissen, S. G.; Reed, S.; Lohse, K. A.; Magnuson, T. S.

    2014-12-01

    Nitrogen, next to water, is believed to be the main limiting resource in arid and semi-arid ecosystems. Biological soil crusts (biocrusts) -a surface community of mosses, lichens and cyanobacteria-have been found to be the main influx of "new" nitrogen (N) into many dryland ecosystems. Controls on biocrust N fixation rates include climate (temperature and moisture), phosphorus availability, and disturbance factors such as trampling, yet a systematic examination of climatic and disturbance controls on biocrusts communities is lacking. Biocrust samples were collected along an elevation gradient in the Reynolds Creek Experimental Watershed near Murphy, Idaho. Four sites were selected from a sagebrush steppe ecosystem with precipitation ranging from ≤250mm/yr to ≥1100mm/yr. Each site included 5 grazed plots and one historic exclosure plot that has been free from grazing for more than 40 years. Five samples each were collected from under plants and from interplant spaces from the grazed plots and exclosures and analyzed for potential N fixation using an acetylene reduction assay. We hypothesized that N fixation rates would be the highest in the exclosures of the two middle sites along the elevation gradient, due to the lack of disturbance and optimal temperature and moisture, respectively. As predicted, results showed higher rates of potential N fixation in exclosures than non-exclosures at a mid-elevation 8.4 ± 3.1 kg N/ha/yr in the exclosures compared to 1.8 ± 1.5 kg N/ha/yr indicating that grazing may reduce N fixation activity. Interestingly, rates were 2-5 times lower under plant canopies compared to interplant spaces at all but the highest elevation site. Findings from our study suggest that biocrust N fixation may be a dominant input of N into theses dryland systems and, in line with our hypotheses, that climate, location within the landscape, and disturbance may interact to regulate the rates of this fundamental ecosystem process.

  11. High potential of nitrogen fixation in pristine, ombrotrophic bogs in Southern Patagonia

    NASA Astrophysics Data System (ADS)

    Knorr, Klaus-Holger; Horn, Marcus A.; Bahamonde Aguilar, Nelson A.; Borken, Werner

    2015-04-01

    Nitrogen (N) input in pristine peatlands occurs via natural input of inorganic N through atmospheric deposition or biological dinitrogen (N2) fixation. However, N2 fixation is to date mostly attributed to bacteria and algae associated to Sphagnum and its contribution to plant productivity and peat buildup has been often underestimated in previous studies. Based on net N storage, exceptionally low N deposition, and high abundance of vascular plants at pristine peatlands in Southern Patagonia, we hypothesized that there must be a high potential of non-symbiotic N2 fixation not limited to the occurrence of Sphagnum. To this end, we chose two ombrotrophic bogs with spots that are dominated either by Sphagnum or by vascular, cushion-forming plants and sampled peat from different depths for incubation with 15N2 to determine N2 fixation potentials. Moreover, we analyzed 15N2 fixation by a nodule-forming, endemic conifer inhabiting the peatlands. Results from 15N2 uptake were compared to the conventional approach to study N2 fixation by the acetylene reduction assay (ARA). Using 15N2 as a tracer, high non-symbiotic N2 fixation rates of 0.3-1.4 μmol N g-1 d-1 were found down to 50 cm under micro-oxic conditions (2 vol.%) in samples from both plots either covered by Sphagnum magellanicum or by vascular cushion plants. Peat N concentrations suggested a higher potential of non-symbiotic N2 fixation under cushion plants, likely because of the availability of easily decomposable organic compounds as substrates and oxic conditions in the rhizosphere. In the Sphagnum plots, high N2 fixation below 10 cm depth would rather reflect a potential fixation that may switch on during periods of low water levels when oxygen penetrates deeper into the peat. 15N natural abundance of live Sphagnum from 0-10 cm pointed to N uptake solely from atmospheric deposition and non-symbiotic N2 fixation. 15N signatures of peat from the cushion plant plots indicated additional N supply from N

  12. Symbiotic Nitrogen Fixation and the Challenges to Its Extension to Nonlegumes.

    PubMed

    Mus, Florence; Crook, Matthew B; Garcia, Kevin; Garcia Costas, Amaya; Geddes, Barney A; Kouri, Evangelia D; Paramasivan, Ponraj; Ryu, Min-Hyung; Oldroyd, Giles E D; Poole, Philip S; Udvardi, Michael K; Voigt, Christopher A; Ané, Jean-Michel; Peters, John W

    2016-07-01

    Access to fixed or available forms of nitrogen limits the productivity of crop plants and thus food production. Nitrogenous fertilizer production currently represents a significant expense for the efficient growth of various crops in the developed world. There are significant potential gains to be had from reducing dependence on nitrogenous fertilizers in agriculture in the developed world and in developing countries, and there is significant interest in research on biological nitrogen fixation and prospects for increasing its importance in an agricultural setting. Biological nitrogen fixation is the conversion of atmospheric N2 to NH3, a form that can be used by plants. However, the process is restricted to bacteria and archaea and does not occur in eukaryotes. Symbiotic nitrogen fixation is part of a mutualistic relationship in which plants provide a niche and fixed carbon to bacteria in exchange for fixed nitrogen. This process is restricted mainly to legumes in agricultural systems, and there is considerable interest in exploring whether similar symbioses can be developed in nonlegumes, which produce the bulk of human food. We are at a juncture at which the fundamental understanding of biological nitrogen fixation has matured to a level that we can think about engineering symbiotic relationships using synthetic biology approaches. This minireview highlights the fundamental advances in our understanding of biological nitrogen fixation in the context of a blueprint for expanding symbiotic nitrogen fixation to a greater diversity of crop plants through synthetic biology. PMID:27084023

  13. Symbiotic Nitrogen Fixation and the Challenges to Its Extension to Nonlegumes

    PubMed Central

    Mus, Florence; Crook, Matthew B.; Garcia, Kevin; Garcia Costas, Amaya; Geddes, Barney A.; Kouri, Evangelia D.; Paramasivan, Ponraj; Ryu, Min-Hyung; Oldroyd, Giles E. D.; Poole, Philip S.; Udvardi, Michael K.; Voigt, Christopher A.

    2016-01-01

    Access to fixed or available forms of nitrogen limits the productivity of crop plants and thus food production. Nitrogenous fertilizer production currently represents a significant expense for the efficient growth of various crops in the developed world. There are significant potential gains to be had from reducing dependence on nitrogenous fertilizers in agriculture in the developed world and in developing countries, and there is significant interest in research on biological nitrogen fixation and prospects for increasing its importance in an agricultural setting. Biological nitrogen fixation is the conversion of atmospheric N2 to NH3, a form that can be used by plants. However, the process is restricted to bacteria and archaea and does not occur in eukaryotes. Symbiotic nitrogen fixation is part of a mutualistic relationship in which plants provide a niche and fixed carbon to bacteria in exchange for fixed nitrogen. This process is restricted mainly to legumes in agricultural systems, and there is considerable interest in exploring whether similar symbioses can be developed in nonlegumes, which produce the bulk of human food. We are at a juncture at which the fundamental understanding of biological nitrogen fixation has matured to a level that we can think about engineering symbiotic relationships using synthetic biology approaches. This minireview highlights the fundamental advances in our understanding of biological nitrogen fixation in the context of a blueprint for expanding symbiotic nitrogen fixation to a greater diversity of crop plants through synthetic biology. PMID:27084023

  14. Role of boron nutrient in nodules growth and nitrogen fixation rates in soybean genotypes under water stress conditions

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Although boron has a stimulatory effect on nodule growth and nitrogen fixation, mechanisms of how boron affects nodules growth and nitrogen fixation, especially under water stress, are still unknown. The stimulatory effect of boron (B) on nodules and nitrogen fixation (NF) is influenced by biotic (s...

  15. Microgravity Effects on the Early Events of Biological Nitrogen Fixation in Medicago Truncatula: Results from the SyNRGE Experiment

    NASA Technical Reports Server (NTRS)

    Stutte, Gary W.; Roberts, Michael

    2012-01-01

    SyNRGE (Symbiotic Nodulation in a Reduced Gravity Environment) was a sortie mission on STS-135 in the Biological Research in Canisters (BRIC) hardware to study the effect of microgravity on a plant-microbe symbiosis resulting in biological nitrogen fixation. Medicago truncatula, a model species for th legume family, was inoculated with its bacterial symbiont, Sinorhizobium meliloti, to observe early biomolecular events associated with infection and nodulation in Petri Dish Fixation Units (PDFU's).

  16. Irreversibly increased nitrogen fixation in Trichodesmium experimentally adapted to elevated carbon dioxide

    PubMed Central

    Hutchins, David A.; Walworth, Nathan G.; Webb, Eric A.; Saito, Mak A.; Moran, Dawn; McIlvin, Matthew R.; Gale, Jasmine; Fu, Fei-Xue

    2015-01-01

    Nitrogen fixation rates of the globally distributed, biogeochemically important marine cyanobacterium Trichodesmium increase under high carbon dioxide (CO2) levels in short-term studies due to physiological plasticity. However, its long-term adaptive responses to ongoing anthropogenic CO2 increases are unknown. Here we show that experimental evolution under extended selection at projected future elevated CO2 levels results in irreversible, large increases in nitrogen fixation and growth rates, even after being moved back to lower present day CO2 levels for hundreds of generations. This represents an unprecedented microbial evolutionary response, as reproductive fitness increases acquired in the selection environment are maintained after returning to the ancestral environment. Constitutive rate increases are accompanied by irreversible shifts in diel nitrogen fixation patterns, and increased activity of a potentially regulatory DNA methyltransferase enzyme. High CO2-selected cell lines also exhibit increased phosphorus-limited growth rates, suggesting a potential advantage for this keystone organism in a more nutrient-limited, acidified future ocean. PMID:26327191

  17. Irreversibly increased nitrogen fixation in Trichodesmium experimentally adapted to elevated carbon dioxide

    NASA Astrophysics Data System (ADS)

    Hutchins, David A.; Walworth, Nathan G.; Webb, Eric A.; Saito, Mak A.; Moran, Dawn; McIlvin, Matthew R.; Gale, Jasmine; Fu, Fei-Xue

    2015-09-01

    Nitrogen fixation rates of the globally distributed, biogeochemically important marine cyanobacterium Trichodesmium increase under high carbon dioxide (CO2) levels in short-term studies due to physiological plasticity. However, its long-term adaptive responses to ongoing anthropogenic CO2 increases are unknown. Here we show that experimental evolution under extended selection at projected future elevated CO2 levels results in irreversible, large increases in nitrogen fixation and growth rates, even after being moved back to lower present day CO2 levels for hundreds of generations. This represents an unprecedented microbial evolutionary response, as reproductive fitness increases acquired in the selection environment are maintained after returning to the ancestral environment. Constitutive rate increases are accompanied by irreversible shifts in diel nitrogen fixation patterns, and increased activity of a potentially regulatory DNA methyltransferase enzyme. High CO2-selected cell lines also exhibit increased phosphorus-limited growth rates, suggesting a potential advantage for this keystone organism in a more nutrient-limited, acidified future ocean.

  18. Regulation of Development and Nitrogen Fixation in Anabaena

    SciTech Connect

    James W. Golden

    2008-10-17

    The regulation of development and cellular differentiation is important for all multicellular organisms. The nitrogen-fixing filamentous cyanobacterium Anabaena (also Nostoc) sp. PCC 7120 (hereafter Anabaena) provides a model of multicellular microbial development and pattern formation. Anabaena reduces N2 to ammonia in specialized terminally differentiated cells called heterocysts. A one-dimensional developmental pattern of single heterocysts regularly spaced along filaments of photosynthetic vegetative cells is established to form a multicellular organism composed of these two interdependent cell types. This multicellular growth pattern, the distinct phylogeny of cyanobacteria, and the suspected antiquity of heterocyst development make this an important model system. Our long-term goal is to understand the regulatory network required for heterocyst development and nitrogen fixation. This project is focused on two key aspects of heterocyst regulation: one, the mechanism by which HetR controls the initiation of differentiation, and two, the cis and trans acting factors required for expression of the nitrogen-fixation (nif) genes. HetR is thought to be a central regulator of heterocyst development but the partners and mechanisms involved in this regulation are unknown. Our recent results indicate that PatS and other signals that regulate heterocyst pattern cannot interact, directly or indirectly, with a R223W mutant of HetR. We plan to use biochemical and genetic approaches to identify proteins that interact with the HetR protein, which will help reveal the mechanisms underlying its regulation of development. Our second goal is to determine how the nif genes are expressed. It is important to understand the mechanisms controlling nif genes since they represent the culmination of the differentiation process and the essence of heterocyst function. The Anabaena genome lacks the genes required for expression of nif genes present in other organisms such as rpoN (sigma 54

  19. Symbiotic nitrogen fixation in an arid ecosystem measured by sup 15 N natural abundance

    SciTech Connect

    Johnson, G.V. )

    1990-05-01

    Plants dependent on nitrogen fixation have an {sup 15}N abundance similar to the atmosphere, while non-nitrogen fixing plants usually are enriched in {sup 15}N and are similar to soil nitrogen values. The natural abundance of {sup 15}N in leaf tissues and soils was determined to evaluate symbiotic nitrogen fixation by several legumes and actinorhizal species in the Sevilleta Long-term Ecological Research area in central New Mexico. Comparison of {delta}{sup 15}N values for the legume Prosopis glandulosa (mesquite) to adjacent Atriplex canascens (fourwing saltbush) indicated that P. glandulosa obtained 66% of its nitrogen by fixation. The legume Hoffmanseggia jamesii was found to be utilizing soil nitrogen. The {delta}{sup 15}N values for the actinorhizal plants, Elaeagnus angustifolia and Cercocarpus montanus, while below values for soil nitrogen, did not differ from associated non-fixing plants.

  20. Role of PII proteins in nitrogen fixation control of Herbaspirillum seropedicae strain SmR1

    PubMed Central

    2011-01-01

    Background The PII protein family comprises homotrimeric proteins which act as transducers of the cellular nitrogen and carbon status in prokaryotes and plants. In Herbaspirillum seropedicae, two PII-like proteins (GlnB and GlnK), encoded by the genes glnB and glnK, were identified. The glnB gene is monocistronic and its expression is constitutive, while glnK is located in the nlmAglnKamtB operon and is expressed under nitrogen-limiting conditions. Results In order to determine the involvement of the H. seropedicae glnB and glnK gene products in nitrogen fixation, a series of mutant strains were constructed and characterized. The glnK- mutants were deficient in nitrogen fixation and they were complemented by plasmids expressing the GlnK protein or an N-truncated form of NifA. The nitrogenase post-translational control by ammonium was studied and the results showed that the glnK mutant is partially defective in nitrogenase inactivation upon addition of ammonium while the glnB mutant has a wild-type phenotype. Conclusions Our results indicate that GlnK is mainly responsible for NifA activity regulation and ammonium-dependent post-translational regulation of nitrogenase in H. seropedicae. PMID:21223584

  1. Understanding the Red Sea nutrient cycle - a first look into nitrogen fixation in the Red Sea

    NASA Astrophysics Data System (ADS)

    Mohamed, Roslinda; Arrieta, Jesus; Alam, Intikhab; Duarte, Carlos

    2016-04-01

    The Red Sea is an elongated and semi-enclosed system bordered by Africa and Saudi Arabia. Positioned in an arid, tropical zone, the system receives high solar irradiance and heat flux, extensive evaporation, low rainfall and therefore high salinity. These harsh environmental conditions has set the Red Sea to be one of the fastest warming and saltiest ecosystem in the world. Although nutrients are known to be at very low concentrations, the ultimately limiting nutrient in the system is still undefined. Therefore, like most other oligotrophic systems, we regard the Red Sea as being nitrogen-limited and we foresee nitrogen fixation as the most probable bottleneck in the Red Sea nitrogen budget. On the basis of metagenomes from pelagic microbial communities along the Red Sea, we looked into the distribution of nitrogenase, an enzyme involved in nitrogen fixation, in this system and provide a first insight into the microbial community that is involved in the process. The implications of this study will not only help improve our understanding of the Red Sea nutrient regime, but may also hint on future ocean responses to rising climates.

  2. Effects of drought on characters related to nitrogen fixation in peanut

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Twelve peanut genotypes were tested under three water regimes in two greenhouses to investigate the effects of drought on biomass production and N2 fixation. Drought reduced biomass production from 36.5 to 56.0% and reduced nitrogen fixation from 26.8 to 68.8%. Most genotypes with high biomass produ...

  3. Responses of soil nitrogen fixation to Spartina alterniflora invasion and nitrogen addition in a Chinese salt marsh.

    PubMed

    Huang, Jingxin; Xu, Xiao; Wang, Min; Nie, Ming; Qiu, Shiyun; Wang, Qing; Quan, Zhexue; Xiao, Ming; Li, Bo

    2016-01-01

    Biological nitrogen fixation (BNF) is the major natural process of nitrogen (N) input to ecosystems. To understand how plant invasion and N enrichment affect BNF, we compared soil N-fixation rates and N-fixing microbes (NFM) of an invasive Spartina alterniflora community and a native Phragmites australis community in the Yangtze River estuary, with and without N addition. Our results indicated that plant invasion relative to N enrichment had a greater influence on BNF. At each N level, the S. alterniflora community had a higher soil N-fixation rate but a lower diversity of the nifH gene in comparison with the native community. The S. alterniflora community with N addition had the highest soil N-fixation rate and the nifH gene abundance across all treatments. Our results suggest that S. alterniflora invasion can increase soil N fixation in the high N-loading estuarine ecosystem, and thus may further mediate soil N availability. PMID:26869197

  4. Responses of soil nitrogen fixation to Spartina alterniflora invasion and nitrogen addition in a Chinese salt marsh

    PubMed Central

    Huang, Jingxin; Xu, Xiao; Wang, Min; Nie, Ming; Qiu, Shiyun; Wang, Qing; Quan, Zhexue; Xiao, Ming; Li, Bo

    2016-01-01

    Biological nitrogen fixation (BNF) is the major natural process of nitrogen (N) input to ecosystems. To understand how plant invasion and N enrichment affect BNF, we compared soil N-fixation rates and N-fixing microbes (NFM) of an invasive Spartina alterniflora community and a native Phragmites australis community in the Yangtze River estuary, with and without N addition. Our results indicated that plant invasion relative to N enrichment had a greater influence on BNF. At each N level, the S. alterniflora community had a higher soil N-fixation rate but a lower diversity of the nifH gene in comparison with the native community. The S. alterniflora community with N addition had the highest soil N-fixation rate and the nifH gene abundance across all treatments. Our results suggest that S. alterniflora invasion can increase soil N fixation in the high N-loading estuarine ecosystem, and thus may further mediate soil N availability. PMID:26869197

  5. Global transcriptional analysis of nitrogen fixation and ammonium repression in root-associated Pseudomonas stutzeri A1501

    PubMed Central

    2010-01-01

    regulatory systems. Furthermore, microarray and mutational analyses revealed that many genes of unknown function may play some essential roles in controlling the expression or activity of nitrogenase. The findings presented here establish the foundation for further studies on the physiological function of nitrogen fixation-inducible genes. PMID:20053297

  6. Nitrogen Fixation Control under Drought Stress. Localized or Systemic?1[OA

    PubMed Central

    Marino, Daniel; Frendo, Pierre; Ladrera, Ruben; Zabalza, Ana; Puppo, Alain; Arrese-Igor, Cesar; González, Esther M.

    2007-01-01

    Legume-Rhizobium nitrogen fixation is dramatically affected under drought and other environmental constraints. However, it has yet to be established as to whether such regulation of nitrogen fixation is only exerted at the whole-plant level (e.g. by a systemic nitrogen feedback mechanism) or can also occur at a local nodule level. To address this question, nodulated pea (Pisum sativum) plants were grown in a split-root system, which allowed for half of the root system to be irrigated at field capacity, while the other half was water deprived, thus provoking changes in the nodule water potential. Nitrogen fixation only declined in the water-deprived, half-root system and this result was correlated with modifications in the activities of key nodule's enzymes such as sucrose synthase and isocitrate dehydrogenase and in nodular malate content. Furthermore, the decline in nodule water potential resulted in a cell redox imbalance. The results also indicate that systemic nitrogen feedback signaling was not operating in these water-stressed plants, since nitrogen fixation activity was maintained at control values in the watered half of the split-root plants. Thus, the use of a partially droughted split-root system provides evidence that nitrogen fixation activity under drought stress is mainly controlled at the local level rather than by a systemic nitrogen signal. PMID:17416644

  7. Rhizobium sp. strain ORS571 ammonium assimilation and nitrogen fixation.

    PubMed Central

    Donald, R G; Ludwig, R A

    1984-01-01

    Among rhizobia studied, Rhizobium sp. strain ORS571 alone grew unambiguously on N2 as sole N source. In ORS571 , only the glutamine synthetase (GS)-glutamate synthase ( GOGAT ) pathway assimilated ammonium. However, ORS571 exhibited two unique physiological aspects of this pathway: ORS571 had only GS I, whereas all other Rhizobiaceae studied had both GS I and GS II, and both NADPH- and NADH-dependent GOGAT activities were present. ORS571 GS-affected and NADPH- GOGAT -affected mutant strains were defective in both ammonium assimilation (Asm-) and N2 fixation (Nif-) in culture and in planta ; NADH- GOGAT mutants were Asm- but Nif+. "Bacteroid" GS activity was essentially nil, suggesting symbiotic ammonium export. Physiological studies on effects of glutamine, ammonium, methionine sulfoximine, and diazo-oxo-norleucine on nitrogenase induction in culture implied a regulatory role for the intracellular glutamine pool. Images PMID:6144666

  8. Short total synthesis of indolizidine alkaloids using the atmospheric nitrogen fixation method

    SciTech Connect

    Mori, Miwako; Hori, Masanori; Sato, Yoshihiro, Sato

    1995-12-31

    The authors have already reported the nitrogen fixation method using N{sub 2}-TiCl{sub 4}-TMSCl-Li system. Now they have succeeded in the incorporation of atmospheric nitrogen into organic compounds and the total synthesis of monomorine I using. From triketone 2 and molecular nitrogen, pyrolizidine and indolizidine derivatives were obtained in good yields. For the synthesis of natural product, monomorine I, using molecular nitrogen, triketone 6 was required, which was easily obtained from cyclopentene derivative 7.

  9. Influence of Co and B12 on the growth and nitrogen fixation of Trichodesmium

    PubMed Central

    Rodriguez, Irene B.; Ho, Tung-Yuan

    2015-01-01

    We investigated the influence of varying cobalt (Co) and B12 concentrations to growth and nitrogen fixation of Trichodesmium, a major diazotroph in the tropical and subtropical oligotrophic ocean. Here we show that sufficient inorganic Co, 20 pmol L-1, sustains the growth of Trichodesmium either with or without an additional B12 supply. We also found that in these culture conditions, nitrogen levels fixed by Trichodesmium were higher in treatments with insufficient B12 than in treatments with higher B12 availability. Under limited inorganic Co availability, ranging from 0.2 to 2 pmol L-1, Trichodesmium growth was significantly compromised in cultures without B12. In these low Co concentrations, addition of 400 pmol L-1 of B12 supported phytoplankton growth indicating that B12 supply augmented for the low Co concentrations. Our study demonstrates that Trichodesmium has an absolute Co requirement, which is not replaceable with Zn, and that B12 supply alleviates stress in cases where Co is limiting. These results show that the interlocking availabilities of Co and B12 may influence the growth and nitrogen fixation of Trichodesmium in the ocean. PMID:26150813

  10. Stimulation of nitrogen fixation in soddy-podzolic soils with fungi

    NASA Astrophysics Data System (ADS)

    Kurakov, A. V.; Prokhorov, I. S.; Kostina, N. V.; Makhova, E. G.; Sadykova, V. S.

    2006-09-01

    Stimulation of nitrogen fixation in soddy-podzolic soils is related to the hydrolytic activity of fungi decomposing plant polymers. It was found that the rate of nitrogen fixation upon the simultaneous inoculation of the strains of nitrogen-fixing bacteria Bacillus cereus var. mycoides and the cellulolytic fungus Trichoderma asperellum into a sterile soil enriched with cellulose or Jerusalem artichoke residues is two to four times higher than upon the inoculation of the strains of Bacillus cereus var. mycoides L1 only. The increase in the nitrogen fixation depended on the resistance of the substrates added into the soil to fungal hydrolysis. The biomass of the fungi decomposing plant polymers increased by two-four times. The nitrogen-fixing activity of the soil decreased when the growth of the fungi was inhibited with cycloheximide, which attested to a close correlation between the intensity of the nitrogen fixation and the decomposition of the plant polymers by fungi. The introduction of an antifungal antibiotic, together with starch or with plant residues, significantly (by 60-90%) decreased the rate of nitrogen fixation in the soll.

  11. Modeled contributions of three types of diazotrophs to nitrogen fixation at Station ALOHA.

    PubMed

    Goebel, Nicole L; Edwards, Christopher A; Church, Matthew J; Zehr, Jonathan P

    2007-11-01

    A diagnostic model based on biomass and growth was used to assess the relative contributions of filamentous nonheterocystous Trichodesmium and unicellular cyanobacteria, termed Groups A and B, to nitrogen fixation at the North Pacific Station ALOHA over a 2-year period. Average (and 95% confidence interval, CI) annual rates of modeled monthly values for Trichodesmium, Group B and Group A were 92 (52), 14 (4) and 12 (8) mmol N per m(2) per year, respectively. The fractional contribution to modeled instantaneous nitrogen fixation by each diazotroph fluctuated on interannual, seasonal and shorter time scales. Trichodesmium fixed substantially more nitrogen in year 1 (162) than year 2 (12). Group B fixed almost two times more nitrogen in year 1 (17) than year 2 (9). In contrast, Group A fixed two times more nitrogen in year 2 (16) than year 1 (8). When including uncertainties in our estimates using the bootstrap approach, the range of unicellular nitrogen fixation extended from 10% to 68% of the total annual rate of nitrogen fixation for all three diazotrophs. Furthermore, on a seasonal basis, the model demonstrated that unicellular diazotrophs fixed the majority (51%-97%) of nitrogen during winter and spring, whereas Trichodesmium dominated nitrogen fixation during summer and autumn (60%-96%). Sensitivity of the modeled rates to some parameters suggests that this unique attempt to quantify relative rates of nitrogen fixation by different diazotrophs may need to be reevaluated as additional information on cell size, variability in biomass and C:N, and growth characteristics of the different cyanobacterial diazotrophs become available. PMID:18043668

  12. The nitrogen regime and biological fixation of nitrogen in moss communities (the Khibiny Mountains)

    NASA Astrophysics Data System (ADS)

    Egorov, V. I.

    2007-04-01

    In the vegetation belts of the Khibiny Mountains, the dynamics of the contents of mineral and easily hydrolyzable (according to Cornfield) nitrogen compounds in the litter and the nitrogen-fixing capacity of epiphytic cyanobacteria on dominant mosses were studied. The nitrogen regime of most moss species was shown to be self-supporting probably due to the intense assimilation of molecular nitrogen by epiphytic cyanobacteria (during the growing period, up to 28% of the total nitrogen content in plants) and the low organic matter production by mosses.

  13. Regional and national significance of biological nitrogen fixation by crops in the United States

    EPA Science Inventory

    Background/Questions/Methods Biological nitrogen fixation by crops (C-BNF) represents one of the largest anthropogenic inputs of reactive nitrogen (N) to land surfaces around the world. In the United States (US), existing estimates of C-BNF are uncertain because of incomplete o...

  14. Nitrogen fixation. (Latest citations from the Selected Water Resources Abstracts database). Published Search

    SciTech Connect

    Not Available

    1993-01-01

    The bibliography contains citations concerning nitrogen fixation in terrestrial and aquatic ecosystems and its impact on future resources. The biochemistry and biophysics of the nitrogen-fixing bacteria, algae, and blue-green algae are discussed. (Contains a minimum of 97 citations and includes a subject term index and title list.)

  15. A Minimal Nitrogen Fixation Gene Cluster from Paenibacillus sp. WLY78 Enables Expression of Active Nitrogenase in Escherichia coli

    PubMed Central

    Zhao, Dehua; Liu, Xiaomeng; Zhang, Bo; Xie, Jianbo; Hong, Yuanyuan; Li, Pengfei; Chen, Sanfeng; Dixon, Ray; Li, Jilun

    2013-01-01

    Most biological nitrogen fixation is catalyzed by molybdenum-dependent nitrogenase, an enzyme complex comprising two component proteins that contains three different metalloclusters. Diazotrophs contain a common core of nitrogen fixation nif genes that encode the structural subunits of the enzyme and components required to synthesize the metalloclusters. However, the complement of nif genes required to enable diazotrophic growth varies significantly amongst nitrogen fixing bacteria and archaea. In this study, we identified a minimal nif gene cluster consisting of nine nif genes in the genome of Paenibacillus sp. WLY78, a gram-positive, facultative anaerobe isolated from the rhizosphere of bamboo. We demonstrate that the nif genes in this organism are organized as an operon comprising nifB, nifH, nifD, nifK, nifE, nifN, nifX, hesA and nifV and that the nif cluster is under the control of a σ70 (σA)-dependent promoter located upstream of nifB. To investigate genetic requirements for diazotrophy, we transferred the Paenibacillus nif cluster to Escherichia coli. The minimal nif gene cluster enables synthesis of catalytically active nitrogenase in this host, when expressed either from the native nifB promoter or from the T7 promoter. Deletion analysis indicates that in addition to the core nif genes, hesA plays an important role in nitrogen fixation and is responsive to the availability of molybdenum. Whereas nif transcription in Paenibacillus is regulated in response to nitrogen availability and by the external oxygen concentration, transcription from the nifB promoter is constitutive in E. coli, indicating that negative regulation of nif transcription is bypassed in the heterologous host. This study demonstrates the potential for engineering nitrogen fixation in a non-nitrogen fixing organism with a minimum set of nine nif genes. PMID:24146630

  16. The Role of Symbiotic Nitrogen Fixation in Sustainable Production of Biofuels

    PubMed Central

    Biswas, Bandana; Gresshoff, Peter M.

    2014-01-01

    With the ever-increasing population of the world (expected to reach 9.6 billion by 2050), and altered life style, comes an increased demand for food, fuel and fiber. However, scarcity of land, water and energy accompanied by climate change means that to produce enough to meet the demands is getting increasingly challenging. Today we must use every avenue from science and technology available to address these challenges. The natural process of symbiotic nitrogen fixation, whereby plants such as legumes fix atmospheric nitrogen gas to ammonia, usable by plants can have a substantial impact as it is found in nature, has low environmental and economic costs and is broadly established. Here we look at the importance of symbiotic nitrogen fixation in the production of biofuel feedstocks; how this process can address major challenges, how improving nitrogen fixation is essential, and what we can do about it. PMID:24786096

  17. The role of symbiotic nitrogen fixation in sustainable production of biofuels.

    PubMed

    Biswas, Bandana; Gresshoff, Peter M

    2014-01-01

    With the ever-increasing population of the world (expected to reach 9.6 billion by 2050), and altered life style, comes an increased demand for food, fuel and fiber. However, scarcity of land, water and energy accompanied by climate change means that to produce enough to meet the demands is getting increasingly challenging. Today we must use every avenue from science and technology available to address these challenges. The natural process of symbiotic nitrogen fixation, whereby plants such as legumes fix atmospheric nitrogen gas to ammonia, usable by plants can have a substantial impact as it is found in nature, has low environmental and economic costs and is broadly established. Here we look at the importance of symbiotic nitrogen fixation in the production of biofuel feedstocks; how this process can address major challenges, how improving nitrogen fixation is essential, and what we can do about it. PMID:24786096

  18. Direct nitrogen fixation at the edges of graphene nanoplatelets as efficient electrocatalysts for energy conversion

    PubMed Central

    Jeon, In-Yup; Choi, Hyun-Jung; Ju, Myung Jong; Choi, In Taek; Lim, Kimin; Ko, Jaejung; Kim, Hwan Kyu; Kim, Jae Cheon; Lee, Jae-Joon; Shin, Dongbin; Jung, Sun-Min; Seo, Jeong-Min; Kim, Min-Jung; Park, Noejung; Dai, Liming; Baek, Jong-Beom

    2013-01-01

    Nitrogen fixation is essential for the synthesis of many important chemicals (e.g., fertilizers, explosives) and basic building blocks for all forms of life (e.g., nucleotides for DNA and RNA, amino acids for proteins). However, direct nitrogen fixation is challenging as nitrogen (N2) does not easily react with other chemicals. By dry ball-milling graphite with N2, we have discovered a simple, but versatile, scalable and eco-friendly, approach to direct fixation of N2 at the edges of graphene nanoplatelets (GnPs). The mechanochemical cracking of graphitic C−C bonds generated active carbon species that react directly with N2 to form five- and six-membered aromatic rings at the broken edges, leading to solution-processable edge-nitrogenated graphene nanoplatelets (NGnPs) with superb catalytic performance in both dye-sensitized solar cells and fuel cells to replace conventional Pt-based catalysts for energy conversion. PMID:23877200

  19. Direct nitrogen fixation at the edges of graphene nanoplatelets as efficient electrocatalysts for energy conversion

    NASA Astrophysics Data System (ADS)

    Jeon, In-Yup; Choi, Hyun-Jung; Ju, Myung Jong; Choi, In Taek; Lim, Kimin; Ko, Jaejung; Kim, Hwan Kyu; Kim, Jae Cheon; Lee, Jae-Joon; Shin, Dongbin; Jung, Sun-Min; Seo, Jeong-Min; Kim, Min-Jung; Park, Noejung; Dai, Liming; Baek, Jong-Beom

    2013-07-01

    Nitrogen fixation is essential for the synthesis of many important chemicals (e.g., fertilizers, explosives) and basic building blocks for all forms of life (e.g., nucleotides for DNA and RNA, amino acids for proteins). However, direct nitrogen fixation is challenging as nitrogen (N2) does not easily react with other chemicals. By dry ball-milling graphite with N2, we have discovered a simple, but versatile, scalable and eco-friendly, approach to direct fixation of N2 at the edges of graphene nanoplatelets (GnPs). The mechanochemical cracking of graphitic C-C bonds generated active carbon species that react directly with N2 to form five- and six-membered aromatic rings at the broken edges, leading to solution-processable edge-nitrogenated graphene nanoplatelets (NGnPs) with superb catalytic performance in both dye-sensitized solar cells and fuel cells to replace conventional Pt-based catalysts for energy conversion.

  20. High cell-specific rates of nitrogen and carbon fixation by the cyanobacterium Aphanizomenon sp. at low temperatures in the Baltic Sea.

    PubMed

    Svedén, Jennie B; Adam, Birgit; Walve, Jakob; Nahar, Nurun; Musat, Niculina; Lavik, Gaute; Whitehouse, Martin J; Kuypers, Marcel M M; Ploug, Helle

    2015-12-01

    Aphanizomenon is a widespread genus of nitrogen (N2)-fixing cyanobacteria in lakes and estuaries, accounting for a large fraction of the summer N2-fixation in the Baltic Sea. However, information about its cell-specific carbon (C)- and N2-fixation rates in the early growth season has not previously been reported. We combined various methods to study N2-fixation, photosynthesis and respiration in field-sampled Baltic Sea Aphanizomenon sp. during early summer at 10°C. Stable isotope incubations at in situ light intensities during 24 h combined with cell-specific secondary ion mass spectrometry showed an average net N2-fixation rate of 55 fmol N cell(-1) day(-1). Dark net N2-fixation rates over a course of 12 h were 20% of those measured in light. C-fixation, but not N2-fixation, was inhibited by high ambient light intensities during daytime. Consequently, the C:N fixation ratio varied substantially over the diel cycle. C- and N2-fixation rates were comparable to those reported for Aphanizomenon sp. in August at 19°C, using the same methods. High respiration rates (23% of gross photosynthesis) were measured with (14)C-incubations and O2-microsensors, and presumably reflect the energy needed for high N2-fixation rates. Hence, Aphanizomenon sp. is an important contributor to N2-fixation at low in situ temperatures in the early growth season. PMID:26511856

  1. Nitrogen fixation island and rhizosphere competence traits in the genome of root-associated Pseudomonas stutzeri A1501

    PubMed Central

    Yan, Yongliang; Yang, Jian; Dou, Yuetan; Chen, Ming; Ping, Shuzhen; Peng, Junping; Lu, Wei; Zhang, Wei; Yao, Ziying; Li, Hongquan; Liu, Wei; He, Sheng; Geng, Lizhao; Zhang, Xiaobing; Yang, Fan; Yu, Haiying; Zhan, Yuhua; Li, Danhua; Lin, Zhanglin; Wang, Yiping; Elmerich, Claudine; Lin, Min; Jin, Qi

    2008-01-01

    The capacity to fix nitrogen is widely distributed in phyla of Bacteria and Archaea but has long been considered to be absent from the Pseudomonas genus. We report here the complete genome sequencing of nitrogen-fixing root-associated Pseudomonas stutzeri A1501. The genome consists of a single circular chromosome with 4,567,418 bp. Comparative genomics revealed that, among 4,146 protein-encoding genes, 1,977 have orthologs in each of the five other Pseudomonas representative species sequenced to date. The genome contains genes involved in broad utilization of carbon sources, nitrogen fixation, denitrification, degradation of aromatic compounds, biosynthesis of polyhydroxybutyrate, multiple pathways of protection against environmental stress, and other functions that presumably give A1501 an advantage in root colonization. Genetic information on synthesis, maturation, and functioning of nitrogenase is clustered in a 49-kb island, suggesting that this property was acquired by lateral gene transfer. New genes required for the nitrogen fixation process have been identified within the nif island. The genome sequence offers the genetic basis for further study of the evolution of the nitrogen fixation property and identification of rhizosphere competence traits required in the interaction with host plants; moreover, it opens up new perspectives for wider application of root-associated diazotrophs in sustainable agriculture. PMID:18495935

  2. Using Synthetic Biology to Distinguish and Overcome Regulatory and Functional Barriers Related to Nitrogen Fixation

    PubMed Central

    Wang, Xia; Yang, Jian-Guo; Chen, Li; Wang, Ji-Long; Cheng, Qi; Dixon, Ray; Wang, Yi-Ping

    2013-01-01

    Biological nitrogen fixation is a complex process requiring multiple genes working in concert. To date, the Klebsiella pneumoniae nif gene cluster, divided into seven operons, is one of the most studied systems. Its nitrogen fixation capacity is subject to complex cascade regulation and physiological limitations. In this report, the entire K. pneumoniae nif gene cluster was reassembled as operon-based BioBrick parts in Escherichia coli. It provided ∼100% activity of native K. pneumoniae system. Based on the expression levels of these BioBrick parts, a T7 RNA polymerase–LacI expression system was used to replace the σ54-dependent promoters located upstream of nif operons. Expression patterns of nif operons were critical for the maximum activity of the recombinant system. By mimicking these expression levels with variable-strength T7-dependent promoters, ∼42% of the nitrogenase activity of the σ54-dependent nif system was achieved in E. coli. When the newly constructed T7-dependent nif system was challenged with different genetic and physiological conditions, it bypassed the original complex regulatory circuits, with minor physiological limitations. Therefore, we have successfully replaced the nif regulatory elements with a simple expression system that may provide the first step for further research of introducing nif genes into eukaryotic organelles, which has considerable potentials in agro-biotechnology. PMID:23935879

  3. Do Fixation Cues Ensure Fixation Accuracy in Split-Fovea Studies of Word Recognition?

    ERIC Educational Resources Information Center

    Jordan, Timothy R.; Paterson, Kevin B.; Kurtev, Stoyan; Xu, Mengyun

    2009-01-01

    Many studies have claimed that hemispheric processing is split precisely at the foveal midline and so place great emphasis on the precise location at which words are fixated. These claims are based on experiments in which a variety of fixation procedures were used to ensure fixation accuracy but the effectiveness of these procedures is unclear. We…

  4. Biotic nitrogen fixation in the bryosphere is inhibited more by drought than warming.

    PubMed

    Whiteley, Jonathan A; Gonzalez, Andrew

    2016-08-01

    The boreal forest is of particular interest to climate change research due to its large circumpolar distribution and accumulated soil carbon pool. Carbon uptake in this ecosystem is nitrogen (N)-limited, therefore factors affecting carbon or nitrogen dynamics in the boreal forest can have consequences for global climate. We used a 2-year field experiment to investigate the response of biotic nitrogen fixation by cyanobacteria associated with boreal forest bryophytes, in a factorial experiment combining simulated climate change with habitat fragmentation treatments. We simulated climate change conditions using open-top greenhouse chambers in the field, which increased mean and maximum temperatures, and created a precipitation gradient from ambient levels in the center to extreme drought conditions at the periphery of the chamber. The dry patches near the chamber walls exhibited almost no N-fixation, despite having similar densities of cyanobacteria (predominantly Stigonema sp.) as other patches. Rates of N-fixation were best explained by a model containing moisture, fragmentation, cyanobacteria density and time; warming was not a significant variable affecting N-fixation. There was no significant interaction between warming and fragmentation. These results suggest that cyanobacteria responded physiologically to drought by reducing N-fixation activity long before any changes in density. Ecosystem processes, such as N-fixation, can respond in the short term to environmental change much more rapidly than changes in the underlying community structure. Such rapid physiological responses may occur faster than demographic insurance effects of biodiversity. PMID:27098528

  5. Nitrogen fixation activity in biological soil crusts dominated by cyanobacteria in the Subpolar Urals (European North-East Russia).

    PubMed

    Patova, Elena; Sivkov, Michail; Patova, Anna

    2016-09-01

    The nitrogen fixation by biological soil crusts with a dominance of cyanobacteria was studied using the acetylene reduction assay in the territory of the Subpolar Urals (65°11' N, 60°18' E), Russia. The field measurements of nitrogen fixation activity were conducted in situ for two different types of soil crusts dominated by Stigonema (V1 type) and Nostoc with Scytonema (V2 type). The nitrogen fixation process had similar dynamics in both crusts but nitrogen fixation rates were different. The crusts of the V2 type showed a significantly higher acetylene reduction activity, with ethylene production rate of 1.76 ± 0.49 g C2H4 m(-2) h(-1) at 15°C, compared with V1-type soil crusts, with a rate of 0.53 ± 0.21 mg C2H4 m(-2) h(-1) at 15°C. The daily value of acetylene reduction activity in V2-type soil crusts was 32.7 ± 6.2 mg C2H4 m(-2) d(-1) and in V1-type crusts, 12.3 ± 1.8 mg C2H4 m(-2) d(-1) After recalculation for N, the daily values of nitrogen fixation were in the range 3.3-22.3 mg N m(-2) d(-1), which is a few times higher than the values of N input from the precipitation to the soil in the studied regions. The dependence of nitrogen-fixation activity on temperature and light intensity of biological soil crusts was investigated. On the basis of temperature models obtained from the dependence, the nitrogen balance was calculated for the growing season (approximately 120 days). The crusts dominated by Stigonema species were fixing 0.3 g N m(-2) (ethylene production rate, 1.10 g C2H4 m(-2)) and crusts dominated by Nostoc and Scytonema were fixing 1.3 g N m(-2) (4.10 g C2H4 m(-2)). PMID:27306556

  6. The Abiotic Fixation of Nitrogen on Terrestrial Planets: Experimental Results and their Implications.

    NASA Astrophysics Data System (ADS)

    Summers, David; Khare, Bishun; Basa, Ranor

    The abiotic fixation of nitrogen is critical to understanding habitability, planetary evolution and the potential origin of life on terrestrial planets. A non-biological source of fixed nitrogen, in a biochemically accessible form, is necessary for the origin and early evolution of life. Loss of atmospheric nitrogen can result in an incapacity to sustain liquid surface water (as on Mars) and impact planetary habitability. The products of fixation will also impact the geochemistry. Shock heating of a non-reducing atmosphere, by meteors or lighting, will produce NO. This process has been well studied. However, our understanding of the subsequent reactions of NO has been, in the past, theoretical. It was postulated that NO was photochemically converted to HNO which then dissolves in surface waters and reacts to form nitrate and nitrite. This chemistry has now been studied experimentally. Our work has observed that there are multiple pathways for the fixation. One pathway observed is consistent with the theoretically predicted route via the formation of HNO. Interestingly, this pathway is coupled to photochemical formation of formaldehyde from CO through the formation of HCO. In the presence of liquid water, this pathway leads to the formation of nitrate and nitrite. In the presence of water vapor, but no liquid water, HNO appears to mostly dimerize to form N2 O. A second pathway involves the formation of NO2 from CO2 and NO. This pathway becomes more dominant without water, but the reaction of NO2 with any form of water, even just adsorbed water, can lead to nitric acid. Finally, with FeS suspended in liquid water, the direct reduction of NO to ammonia is observed. This last pathway represents the most efficient way to reduced nitrogen, with product yields in excess of 50% (nitrite/nitrate, from the first two pathways can also be reduced to ammonia thought the overall efficiency suffers). This has implications for a number of planets. For example, chemistry in the

  7. Enzymology of biological nitrogen fixation. Final report, May 1, 1987--April 30, 1996

    SciTech Connect

    1997-05-01

    Biological nitrogen fixation is of central importance in the earth`s nitrogen economy. Fixation of nitrogen is accomplished by a variety of microorganisms, all of them procaryotic. Some operate independently and some function symbiotically or associatively with photosynthesizing plants. Biological nitrogen fixation is accomplished via the reaction: N{sub 2} + 8H{sup +} + 8e{sup {minus}} {yields} 2NH{sub 3} + H{sub 2}. This reaction requires a minimum of 16 ATP under ideal laboratory conditions, so it is obvious that the energy demand of the reaction is very high. When certain nitrogen-fixing organisms are supplied fixed nitrogen (e.g., ammonium) the organisms use the fixed nitrogen and turn off their nitrogenase system, thus conserving energy. When the fixed nitrogen is exhausted, the organism reactivates its nitrogenase. The system is turned off by dinitrogenase reductase ADP-ribosyl transferase (DRAT) and turned back on by dinitrogenase reductase-activating glycohydrolase (DRAG). The authors have investigated the details of how DRAT and DRAG are formed, how they function, and the genetics of their formation and operation.

  8. Nitrogen limitation and nitrogen fixation during alkane biodegradation in a sandy soil.

    PubMed Central

    Toccalino, P L; Johnson, R L; Boone, D R

    1993-01-01

    We investigated nutrient limitations during hydrocarbon degradation in a sandy soil and found that fixed nitrogen was initially a limiting nutrient but that N limitation could sometimes be overcome by N2 fixation. Hydrocarbon biodegradation was examined in an unsaturated sandy soil incubated aerobically at 20 degrees C with propane or butane and various added nutrients. Propane and butane degradation proceeded similarly during the first 3 months of incubation. That is, bacteria in soil amended with N oxidized these hydrocarbons more rapidly than in controls without nutrient additions or in soil with added phosphate or trace minerals. Both propane- and butane-amended soil apparently became N limited after the initial available inorganic N was utilized, as indicated by a decrease in the rates of hydrocarbon degradation. After 3 months, propane and butane degradation proceeded differently. Bacteria in propane-degrading soil apparently remained N limited because propane degradation rates stayed low unless more N was added. In contrast, bacteria in butane-degrading soil appeared to overcome their N limitation because butane degradation rates later increased regardless of whether more N was added. Analyses of total N and acetylene reduction assays supported this apparent surplus of N in butane-amended soil. Total N was significantly (P < 0.01) higher in soil incubated with butane and no N amendments than in soil incubated with propane, even when the latter was amended with N. Acetylene reduction occurred only in butane-amended soil. These results indicate that N2 fixation occurred in butane-amended soil but not in propane-amended soil. PMID:8215369

  9. Soybean nodulation and symbiotic nitrogen fixation in response to soil compaction and mulching

    NASA Astrophysics Data System (ADS)

    Siczek, A.; Lipiec, J.

    2009-04-01

    Symbiotic nitrogen fixation by legume crops such as soybean plays a key role in supplying nitrogen for agricultural systems. In symbiotic associations with Bradyrhizobium japonicum soybean can fix up to 200 kg N ha-1 yr-1. This reduces the need for expensive and often environmentally harmful because of leaching nitrogen fertilization. However both soybean nodulation and nitrogen fixation are sensitive to soil conditions. One of the critical soil constraints is soil compaction. Increasing use of heavy equipment and intensive cropping in modern agriculture leads to excessive soil compaction. Compaction often is found as a result of field operations that have to be performed in a very short period of time and when soils are wet and more susceptible to compaction. This results in unfavourable water content, temperature, aeration, pore size distribution, strength for plant growth and microbial activity. The surface mulching can alleviate the adverse effect of the environmental factors on soil by decreasing fluctuation of soil temperature, increasing moisture by controlling evaporation from the soil surface, decreasing bulk density, preventing soil crusting. The effect of mulch on soil conditions largely depends on soil compaction and weather conditions during growing season. The positive effect of the straw mulch on soil moisture has been seen under seasons with insufficient rainfalls. However thicker layers of mulch can act as diffusion barrier, especially when the mulch is wet. Additionally, low soil temperature prevalent during early spring under mulch can impede development of nodule, nodule size and delay onset of nodulation. The aim of this study was to determine the effect of the straw mulch on nodulation and nitrogen fixation of soybean in variously compacted soil. The experimental field was 192 m2and was divided into three parts composed of 6 micro-plots with area 7 m2. Three degrees of soil compaction obtained in each field part through tractor passes were

  10. Nitrogen fixation (Acetylene Reduction) by annual winter legumes on a coal surface mine

    SciTech Connect

    Gabrielson, F.C.

    1982-01-01

    The winter annuals, crimson clover, rose clover, subterranean clover and hairy vetch, were evaluated for nitrogen fixing capacity on coal surface mine substrates by measuring their ability to reduce acetylene to ethylene. The effects of fertilizer, Abruzzi rye, Kentucky 31 fescue grass and a phytotoxic plant Chenopodium album on nitrogen fixation were also assessed. Crimson clover was recommended as the best legume to use on topsoil and shale in the south. Hairy vetch gave good results on shale and subterranean clover did well on topsoil. The use of these species for revegetation is discussed. Overall, no correlation between substrate pH and ethylene levels was found and effects of substrate depended upon the legume species. Super phosphate fertilizer supported less nitrogen fixation than 13-13-13. Abruzzi rye in some unknown way inhibited plant density and nitrogen fixation by legumes but not by free living substrate micro-organisms. Shale from under dead Chenopodium plants in both field and greehouse experiments did not inhibit nitrogen fixation. 7 tables.

  11. Nitrogen fixation (acetylene reduction) by annual winter legumes on a coal surface mine

    SciTech Connect

    Gabrielson, F.C.

    1982-01-01

    The winter annuals, crimson clover, rose clover, subterranean clover and hairy vetch, were evaluated for their ability to fix nitrogen on coal surface mine substrates by measuring their ability to reduce acetylene to ethylene. The effects of fertilizer, Abruzzi ryegrass, Kentucky 31 fescue grass and a phytotoxic plant Chenopodium album on nitrogen fixation was also assessed. Crimson clover was recommended as the best legume to use on topsoil and shale in the South. Hairy vetch gave good results on shale and subterranean clover did well on topsoil. The use of these species for revegetation is discussed. Overall, no correlation between substrate pH and ethylene levels was found and effects of substrate depended upon the legume species. Super phosphate fertilizer supported less nitrogen fixation than 13-13-13. Abruzzi ryegrass in some unknown way inhibited plant density and nitrogen fixation by legumes but not by free living substrate micro-organisms. Shale from under dead Chenopodium plants in both field and greenhouse experiments did not inhibit nitrogen fixation. 11 references, 7 tables.

  12. OxyR-regulated catalase activity is critical for oxidative stress resistance, nodulation and nitrogen fixation in Azorhizobium caulinodans.

    PubMed

    Zhao, Yue; Nickels, Logan M; Wang, Hui; Ling, Jun; Zhong, Zengtao; Zhu, Jun

    2016-07-01

    The legume-rhizobial interaction results in the formation of symbiotic nodules in which rhizobia fix nitrogen. During the process of symbiosis, reactive oxygen species (ROS) are generated. Thus, the response of rhizobia to ROS is important for successful nodulation and nitrogen fixation. In this study, we investigated how Azorhizobium caulinodans, a rhizobium that forms both root and stem nodules on its host plant, regulates ROS resistance. We found that in-frame deletions of a gene encoding the putative catalase-peroxidase katG or a gene encoding a LysR-family regulatory protein, oxyR, exhibited increased sensitivity to H2O2 We then showed that OxyR positively regulated katG expression in an H2O2-independent fashion. Furthermore, we found that deletion of katG or oxyR led to significant reduction in the number of stem nodules and decrease of nitrogen fixation capacities in symbiosis. Our results revealed that KatG and OxyR are not only critical for antioxidant defense in vitro, but also important for nodule formation and nitrogen fixation during interaction with plant hosts. PMID:27190162

  13. Nitrogen limiation and nitrogen fixation during alkane biodegradation in a sandy soil

    SciTech Connect

    Toccalino, P.L.; Johnson, R.L.; Boone, D.R. )

    1993-09-01

    Leaking underground storage tanks are a significant source of petroleum hydrocarbon contamination in soils and ground water. Hydrocarbon biodegradation studies have been conducted in both ground water and topsoil regions, but few studies have been done on the unsaturated zone between these two. This study examines the effects of Nitrogen on propane and butane biodegradiations in an unsaturated sandy soil. Results indicate that nitrogen additions initially stimulated both propane and butane oxidizing organisms in the soil, but that propane-amended soil became N limited whereas butane-amended soil eventually overcame its N limitations by fixing Nitrogen and that nitrogen fixing organisms grew in butane amended but not in propane amended soil. 27 refs., 6 figs.

  14. Expression of an alternative nitrogen fixation system in Azotobacter vinelandii.

    PubMed Central

    Bishop, P E; Jarlenski, D M; Hetherington, D R

    1982-01-01

    Nitrogenase activities were determined from maximum acetylene reduction rates for mutant strains of Azotobacter vinelandii which are unable to fix N2 in the presence of molybdenum (Nif-) but undergo phenotypic reversal to Nif+ under conditions of Mo deficiency. The system responsible for N2 fixation under these conditions is thought to be an alternative N2 fixation system (Bishop et al., Proc. Natl. Acad. Sci. U.S.A. 77:7342-7346, 1980). Phenotypic reversal of Nif- strains to Nif+ strains was also observed in N-free medium without Mo but with either V or Re. Two protein patterns were found on two-dimensional gels of proteins from the extracts of wild-type cells cultured in N-free medium without Mo and with or without V or Re. The expression of each protein pattern in the wild-type strain of A. vinelandii seemed to depend upon the physiological state of the N2-fixing culture. Electron paramagnetic resonance experiments were conducted on whole cells of A. vinelandii grown under conditions of Mo deprivation in the absence of fixed N. No g = 3.65 signal (an electron paramagnetic resonance signal characteristic of the Mo-containing component of nitrogenase) was detectable in these cells, regardless of whether V or Re was present during growth of these cells, These results are discussed from the perspective that the well-known effect of V on N2 fixation by A. vinelandii may involve an alternative N2 fixation system. Images PMID:6281240

  15. Selection and breeding of corn to enhance associative bacterial nitrogen fixation

    SciTech Connect

    Ela, S.W.; Anderson, M.A.; Brill, W.J.

    1980-01-01

    We have increased, through screening and breeding, the ability of corn (maize, Zea mays L.) to support bacterial nitrogen fixation in or on corn roots. Isotopic N fixed from /sup 15/N/sub 2/ was found on the roots. Even though the nitrogen-fixing association depends on germ plasm from tropical corn, the activity can be bred into corn currently used in midwestern United States agriculture.

  16. Nitrogen fixation in sediments along a depth transect through the Peruvian oxygen minimum zone

    NASA Astrophysics Data System (ADS)

    Gier, Jessica; Sommer, Stefan; Löscher, Carolin R.; Dale, Andrew W.; Schmitz, Ruth A.; Treude, Tina

    2016-07-01

    The potential coupling of nitrogen (N2) fixation and sulfate reduction (SR) was explored in sediments of the Peruvian oxygen minimum zone (OMZ). Sediment samples were retrieved by a multiple corer at six stations along a depth transect (70-1025 m water depth) at 12° S, covering anoxic and hypoxic bottom water conditions. Benthic N2 fixation, determined by the acetylene reduction assay, was detected at all sites, with highest rates between 70 and 253 m and lower rates at greater depth. SR rates decreased with increasing water depth. N2 fixation and SR overlapped in sediments, suggesting a potential coupling of both processes. However, a weak positive correlation of their activity distribution was detected by principle component analysis. A potential link between N2 fixation and sulfate-reducing bacteria was indicated by the molecular analysis of nifH genes. Detected nifH sequences clustered with the sulfate-reducing bacteria Desulfonema limicola at the 253 m station. However, nifH sequences of other stations clustered with uncultured organisms, Gammaproteobacteria, and Firmicutes (Clostridia) rather than with known sulfate reducers. The principle component analysis revealed that benthic N2 fixation in the Peruvian OMZ is controlled by organic matter (positive) and free sulfide (negative). No correlation was found between N2 fixation and ammonium concentrations (even at levels > 2022 µM). N2 fixation rates in the Peruvian OMZ sediments were in the same range as those measured in other organic-rich sediments.

  17. Nitrogen fixation and nifH diversity in human gut microbiota.

    PubMed

    Igai, Katsura; Itakura, Manabu; Nishijima, Suguru; Tsurumaru, Hirohito; Suda, Wataru; Tsutaya, Takumi; Tomitsuka, Eriko; Tadokoro, Kiyoshi; Baba, Jun; Odani, Shingo; Natsuhara, Kazumi; Morita, Ayako; Yoneda, Minoru; Greenhill, Andrew R; Horwood, Paul F; Inoue, Jun-Ichi; Ohkuma, Moriya; Hongoh, Yuichi; Yamamoto, Taro; Siba, Peter M; Hattori, Masahira; Minamisawa, Kiwamu; Umezaki, Masahiro

    2016-01-01

    It has been hypothesized that nitrogen fixation occurs in the human gut. However, whether the gut microbiota truly has this potential remains unclear. We investigated the nitrogen-fixing activity and diversity of the nitrogenase reductase (NifH) genes in the faecal microbiota of humans, focusing on Papua New Guinean and Japanese individuals with low to high habitual nitrogen intake. A (15)N2 incorporation assay showed significant enrichment of (15)N in all faecal samples, irrespective of the host nitrogen intake, which was also supported by an acetylene reduction assay. The fixed nitrogen corresponded to 0.01% of the standard nitrogen requirement for humans, although our data implied that the contribution in the gut in vivo might be higher than this value. The nifH genes recovered in cloning and metagenomic analyses were classified in two clusters: one comprising sequences almost identical to Klebsiella sequences and the other related to sequences of Clostridiales members. These results are consistent with an analysis of databases of faecal metagenomes from other human populations. Collectively, the human gut microbiota has a potential for nitrogen fixation, which may be attributable to Klebsiella and Clostridiales strains, although no evidence was found that the nitrogen-fixing activity substantially contributes to the host nitrogen balance. PMID:27554344

  18. Nitrogen fixation and nifH diversity in human gut microbiota

    PubMed Central

    Igai, Katsura; Itakura, Manabu; Nishijima, Suguru; Tsurumaru, Hirohito; Suda, Wataru; Tsutaya, Takumi; Tomitsuka, Eriko; Tadokoro, Kiyoshi; Baba, Jun; Odani, Shingo; Natsuhara, Kazumi; Morita, Ayako; Yoneda, Minoru; Greenhill, Andrew R.; Horwood, Paul F.; Inoue, Jun-ichi; Ohkuma, Moriya; Hongoh, Yuichi; Yamamoto, Taro; Siba, Peter M.; Hattori, Masahira; Minamisawa, Kiwamu; Umezaki, Masahiro

    2016-01-01

    It has been hypothesized that nitrogen fixation occurs in the human gut. However, whether the gut microbiota truly has this potential remains unclear. We investigated the nitrogen-fixing activity and diversity of the nitrogenase reductase (NifH) genes in the faecal microbiota of humans, focusing on Papua New Guinean and Japanese individuals with low to high habitual nitrogen intake. A 15N2 incorporation assay showed significant enrichment of 15N in all faecal samples, irrespective of the host nitrogen intake, which was also supported by an acetylene reduction assay. The fixed nitrogen corresponded to 0.01% of the standard nitrogen requirement for humans, although our data implied that the contribution in the gut in vivo might be higher than this value. The nifH genes recovered in cloning and metagenomic analyses were classified in two clusters: one comprising sequences almost identical to Klebsiella sequences and the other related to sequences of Clostridiales members. These results are consistent with an analysis of databases of faecal metagenomes from other human populations. Collectively, the human gut microbiota has a potential for nitrogen fixation, which may be attributable to Klebsiella and Clostridiales strains, although no evidence was found that the nitrogen-fixing activity substantially contributes to the host nitrogen balance. PMID:27554344

  19. Nitrogen fixation rates at BATS and along the North Atlantic subtropical front

    NASA Astrophysics Data System (ADS)

    Charoenpong, C.; Larkum, J.; Lee, E. M.; Moisander, P.; Altabet, M. A.

    2012-12-01

    Nitrogen fixation is one of the major inputs of new N into the oligotrophic gyre of North Atlantic. In the Bermuda Atlantic Time-series Study (BATS), Trichodesmium spp. and diatom symbiont Richelia have been regarded as a major contributor to the newly fixed N. However, studies using nitrogenase gene (nifH) sequences have indicated a more diverse diazotroph assemblages including unicellular cyanobacteria in this oligotrophic system. Here, we report N2 fixation rates from diazotrophs of the size fraction that includes unicellular cyanobacteria and other bacteria. Samples were taken from BATS and several stations along the meridional transect from BATS southward to the area of the subtropical front (~27oN). Whole water samples were enriched with 15N-labelled N2, and incubated for 12-24 hours in simulated in situ conditions. Post-incubation filtration by using 20 micron size fractionation excluded Trichodesmium and potential diatom symbionts and constrained our rates to smaller non-filamentous N2-fixers. Sampling was conducted on two cruises during July and August 2012. 13C incorporation rates are also presented to show the photosynthetic activity. In addition, the 15N-enrichment of dissolved organic N (DON) was investigated in order to demonstrate the contribution of the diazotrophy to the regenerated nutrient and the potential link to the heterotrophic bacterial production.

  20. Denitrification and Nitrogen Fixation Dynamics in the Area Surrounding an Individual Ghost Shrimp (Neotrypaea californiensis) Burrow System

    PubMed Central

    Bertics, Victoria J.; Sohm, Jill A.; Magnabosco, Cara

    2012-01-01

    Bioturbated sediments are thought of as areas of increased denitrification or fixed-nitrogen (N) loss; however, recent studies have suggested that not all N may be lost from these environments, with some N returning to the system via microbial dinitrogen (N2) fixation. We investigated denitrification and N2 fixation in an intertidal lagoon (Catalina Harbor, CA), an environment characterized by bioturbation by thalassinidean shrimp (Neotrypaea californiensis). Field studies were combined with detailed measurements of denitrification and N2 fixation surrounding a single ghost shrimp burrow system in a narrow aquarium (15 cm by 20 cm by 5 cm). Simultaneous measurements of both activities were performed on samples taken within a 1.5-cm grid for a two-dimensional illustration of their intensity and distribution. These findings were then compared with rate measurements performed on bulk environmental sediment samples collected from the lagoon. Results for the aquarium indicated that both denitrification and N2 fixation have a patchy distribution surrounding the burrow, with no clear correlation to each other, sediment depth, or distance from the burrow. Field denitrification rates were, on average, lower in a bioturbated region than in a seemingly nonbioturbated region; however, replicates showed very high variability. A comparison of denitrification field results with previously reported N2 fixation rates from the same lagoon showed that in the nonbioturbated region, depth-integrated (10 cm) denitrification rates were higher than integrated N2 fixation rates (∼9 to 50 times). In contrast, in the bioturbated sediments, depending on the year and bioturbation intensity, some (∼6.2%) to all of the N lost via denitrification might be accounted for via N2 fixation. PMID:22447588

  1. OVEREXPRESSION OF A NODULE-ENHANCED MALATE DEHYDROGENASE INCREASES NITROGEN FIXATION IN ALFALFA

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Malate is crucial for symbiotic dinitrogen (N2) fixation, occurring in high concentrations in N2-fixing nodules as the major carbon source for bacteroid respiration. Malate also provides carbon skeletons for the assimilation of fixed nitrogen from ammonia into amino acids and is proposed to be invol...

  2. Application of plant genomics for improved symbiotic nitrogen fixation in plants

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Because genome sequencing, transcript profiling, proteome analysis, metabolite profiling, mutant analysis, and comparative genomics have progressed at a logarithmic pace, we know more about the plant genes involved in symbiotic nitrogen fixation (SNF) than could have been imagined a decade ago. Howe...

  3. Soil spatial variability and symbiotic nitrogen fixation by legumes

    SciTech Connect

    Reichardt, K. )

    1990-09-01

    The isotope dilution method for the estimation of N{sub 2} fixation by legumes is analyzed, comparing the application of {sup 15}N-enriched fertilizer with {sup 15}N-labeled soil. Soil variability of other dynamic processes in the soil are discussed in light of the distribution of the {sup 15}N label in the system. Field data were collected along six transects, 45 m long, with 30 plots (replicates) each. The legume (Vicia faba L.) was used as a fixing crop, barley (Hordeum vulgare L.) and oil radish (Raphinus sativus L.) as nonfixing standard crops. Isotope methods were also compared with the yield difference method. Results show that isotope methods were very sensitive to the distribution of the label in the soil and that dynamic processes involving N can significantly affect this distribution over a whole field. Best results were obtained with {sup 15}N-labeled soil. The particular site used, having been farmed for more than 20 years with {sup 15}N trials, showed a homogeneous residual {sup 15}N label that made it possible to estimate N{sub 2} fixation without the application of extra label. Estimates of N{sub 2} fixation with the isotope method were well correlated with the yield difference method when fertilizer use efficiency of the fixing and nonfixing crops were similar. Results also indicate that a good reference crop for one method might not be the best for the other method, and one reason for this is the variability of soil parameters and of dynamic processes occurring in the soil.

  4. Seasonally dependent iron limitation of nitrogen fixation in tropical forests of karst landscapes

    NASA Astrophysics Data System (ADS)

    Winbourne, J. B.; Brewer, S.; Houlton, B. Z.

    2015-12-01

    Limestone tropical forests in karst topography are one of the most poorly studied ecosystems on Earth, and has been substantially cleared by human activities throughout much of Central America. This ecosystem is noted for its high level of plant productivity, biomass, endemism and biological diversity compared to nearby neighboring tropical forests on volcanic rock substrates (Brewer et al. 2002). A question remains as to how limestone tropical forests are able to maintain the high nutrient demands of plant photosynthesis and tree biomass growth. Here, we demonstrate that rates of nitrogen (N) fixation are higher in limestone versus volcanic soil substrates, with direct evidence for the emergence of seasonally dependent iron limitation of N fixation in limestone tropical forest. N fixation rates showed a three-fold increase in response to iron additions, especially during the wet season when N demands of the forest trees are highest. In contrast, adjacent forests growing on the more classical acidic volcanic soils showed no response to iron or other nutrient additions. Biologically available pools of iron were exceedingly low in the limestone forest site, consistent with the complexation of iron under high pH conditions. Biological acquisition of iron, as measured by the concentration of iron chelating compounds (i.e. siderophores), provided additional evidence for iron limitation of microbial processes in limestone tropical forests, where concentrations were six times higher than those at the volcanic site. Our results suggest that the functioning of limestone tropical forest is strongly regulated by interactions between iron, soil pH, and N cycling.

  5. Biological nitrogen fixation in sugar cane: A key to energetically viable biofuel production

    SciTech Connect

    Boddey, R.M.

    1995-05-01

    The advantages of producing biofuels to replace fossil energy sources are derived from the fact that the energy accumulated in the biomass in captured directly from photosynthesis and is thus renewable, and that the cycle of carbon dioxide fixation by the crop, followed by burning of the fuel makes no overall contribution to atmospheric CO{sub 2} or, consequently, to global warming. However, these advantages are negated if large quantities of fossil fuels need to be used to grow or process the biofuel crop. In this regard, the Brazilian bioethanol program, based on the fermentation/distillation of sugar cane juice, is particularly favorable, not only because the crop is principally hand harvested, but also because of the low nitrogen fertilizer use on sugar cane in Brazil. Recent {sup 15}N and N balance studies have shown that in some Brazilian cane varieties, high yields are possible without N fertilization because the plants are able to obtain large contributions of nitrogen from plant-associated biological N{sub 2} fixation (BNF). The N{sub 2}-fixing acid-tolerant bacterium Acetobacter diazotrophicus was first found to occur within roots, stems, and leaves of sugar cane. Subsequently, two species of Herbaspirillum also have been found to occur within the interior of all sugar cane tissues. The discovery of these, and other N{sub 2}-fixing bacteria that survive poorly in soil but thrive within plant tissue (endophytic bacteria), may account for the high BNF contributions observed in sugar cane. Further study of this system should allow the gradual elimination of N fertilizer use on sugar cane, at least in Brazil, and opens up the possibility of the extension of this efficient N{sub 2}-fixing system to cereal and other crops with consequent immense potential benefits to tropical agriculture. 44 refs., 9 figs., 4 tabs.

  6. Regional constraints to biological nitrogen fixation in post-fire forest communities

    USGS Publications Warehouse

    Yelenik, Stephanie; Perakis, Steven S.; Hibbs, David

    2013-01-01

    Biological nitrogen fixation (BNF) is a key ecological process that can restore nitrogen (N) lost in wildfire and shape the pace and pattern of post-fire forest recovery. To date, there is limited information on how climate and soil fertility interact to influence different pathways of BNF in early forest succession. We studied asymbiotic (forest floor and soil) and symbiotic (the shrub Ceanothus integerrimus) BNF rates across six sites in the Klamath National Forest, California, USA. We used combined gradient and experimental phosphorus (P) fertilization studies to explore cross-site variation in BNF rates and then related these rates to abiotic and biotic variables. We estimate that our measured BNF rates 22 years after wildfire (6.1–12.1 kg N·ha-1·yr-1) are unlikely to fully replace wildfire N losses. We found that asymbiotic BNF is P limited, although this is not the case for symbiotic BNF in Ceanothus. In contrast, Ceanothus BNF is largely driven by competition from other vegetation: in high-productivity sites with high potential evapotranspiration (Et), shrub biomass is suppressed as tree biomass increases. Because shrub biomass governed cross-site variation in Ceanothus BNF, this competitive interaction led to lower BNF in sites with high productivity and Et. Overall, these results suggest that the effects of nutrients play a larger role in driving asymbiotic than symbiotic fixation across our post-fire sites. However, because symbiotic BNF is 8–90x greater than asymbiotic BNF, it is interspecific plant competition that governs overall BNF inputs in these forests.

  7. Potential for Nitrogen Fixation in Maize Genotypes in Brazil

    PubMed Central

    Von Bülow, Joachim F. W.; Döbereiner, Johanna

    1975-01-01

    N2 fixation in field-grown maize (Zea mays L.) plants was estimated by a nondestructive acetylene reduction method which permitted the plants to continue growing and produce seeds. Samples from six areas revealed mean nitrogenase activities of 74-2167 nmol of C2H4/(g of dry roots × hr) for 10 plants. Among 276 S1 lines planted in two field experiments, 17 lines were selected for further nitrogenase activity assays after prescreening. Variability within lines was high but significant differences among lines were obtained in one experiment. The best lines showed mean nitrogenase activities of 2026, 2315, and 7124 nmol of C2H4/(g of dry roots × hr), whereas the original cultivar reduced only 313 nmol. The highest value approaches the nitrogenase activity of soybean. If the theoretical 3:1 (C2H4/N2 reduced) conversion factor is used, a potential daily N2 fixation of 2 kg of N2/hectare can be calculated. Periodic sampling within a brachytic maize cultivar revealed that maximum nitrogenase activity occurred at about the 75% silking stage. Soil effects also were pronounced. N2-fixing Spirillum sp. could be isolated from all active root pieces when they were surface sterilized. These organisms appear to be primarily responsible for root nitrogenase activity in maize. PMID:16592251

  8. The effect of nutrients on carbon and nitrogen fixation by the UCYN-A-haptophyte symbiosis.

    PubMed

    Krupke, Andreas; Mohr, Wiebke; LaRoche, Julie; Fuchs, Bernhard M; Amann, Rudolf I; Kuypers, Marcel M M

    2015-07-01

    Symbiotic relationships between phytoplankton and N2-fixing microorganisms play a crucial role in marine ecosystems. The abundant and widespread unicellular cyanobacteria group A (UCYN-A) has recently been found to live symbiotically with a haptophyte. Here, we investigated the effect of nitrogen (N), phosphorus (P), iron (Fe) and Saharan dust additions on nitrogen (N2) fixation and primary production by the UCYN-A-haptophyte association in the subtropical eastern North Atlantic Ocean using nifH expression analysis and stable isotope incubations combined with single-cell measurements. N2 fixation by UCYN-A was stimulated by the addition of Fe and Saharan dust, although this was not reflected in the nifH expression. CO2 fixation by the haptophyte was stimulated by the addition of ammonium nitrate as well as Fe and Saharan dust. Intriguingly, the single-cell analysis using nanometer scale secondary ion mass spectrometry indicates that the increased CO2 fixation by the haptophyte in treatments without added fixed N is likely an indirect result of the positive effect of Fe and/or P on UCYN-A N2 fixation and the transfer of N2-derived N to the haptophyte. Our results reveal a direct linkage between the marine carbon and nitrogen cycles that is fuelled by the atmospheric deposition of dust. The comparison of single-cell rates suggests a tight coupling of nitrogen and carbon transfer that stays balanced even under changing nutrient regimes. However, it appears that the transfer of carbon from the haptophyte to UCYN-A requires a transfer of nitrogen from UCYN-A. This tight coupling indicates an obligate symbiosis of this globally important diazotrophic association. PMID:25535939

  9. Abiotic nitrogen fixation on terrestrial planets: reduction of NO to ammonia by FeS.

    PubMed

    Summers, David P; Basa, Ranor C B; Khare, Bishun; Rodoni, David

    2012-02-01

    Understanding the abiotic fixation of nitrogen and how such fixation can be a supply of prebiotic nitrogen is critical for understanding both the planetary evolution of, and the potential origin of life on, terrestrial planets. As nitrogen is a biochemically essential element, sources of biochemically accessible nitrogen, especially reduced nitrogen, are critical to prebiotic chemistry and the origin of life. Loss of atmospheric nitrogen can result in loss of the ability to sustain liquid water on a planetary surface, which would impact planetary habitability and hydrological processes that shape the surface. It is known that NO can be photochemically converted through a chain of reactions to form nitrate and nitrite, which can be subsequently reduced to ammonia. Here, we show that NO can also be directly reduced, by FeS, to ammonia. In addition to removing nitrogen from the atmosphere, this reaction is particularly important as a source of reduced nitrogen on an early terrestrial planet. By converting NO directly to ammonia in a single step, ammonia is formed with a higher product yield (~50%) than would be possible through the formation of nitrate/nitrite and subsequent conversion to ammonia. In conjunction with the reduction of NO, there is also a catalytic disproportionation at the mineral surface that converts NO to NO₂ and N₂O. The NO₂ is then converted to ammonia, while the N₂O is released back in the gas phase, which provides an abiotic source of nitrous oxide. PMID:22283408

  10. The Role of Nitrogen Fixation in Cyanobacterial Bloom Toxicity in a Temperate, Eutrophic Lake

    PubMed Central

    Beversdorf, Lucas J.; Miller, Todd R.; McMahon, Katherine D.

    2013-01-01

    Toxic cyanobacterial blooms threaten freshwaters worldwide but have proven difficult to predict because the mechanisms of bloom formation and toxin production are unknown, especially on weekly time scales. Water quality management continues to focus on aggregated metrics, such as chlorophyll and total nutrients, which may not be sufficient to explain complex community changes and functions such as toxin production. For example, nitrogen (N) speciation and cycling play an important role, on daily time scales, in shaping cyanobacterial communities because declining N has been shown to select for N fixers. In addition, subsequent N pulses from N2 fixation may stimulate and sustain toxic cyanobacterial growth. Herein, we describe how rapid early summer declines in N followed by bursts of N fixation have shaped cyanobacterial communities in a eutrophic lake (Lake Mendota, Wisconsin, USA), possibly driving toxic Microcystis blooms throughout the growing season. On weekly time scales in 2010 and 2011, we monitored the cyanobacterial community in a eutrophic lake using the phycocyanin intergenic spacer (PC-IGS) region to determine population dynamics. In parallel, we measured microcystin concentrations, N2 fixation rates, and potential environmental drivers that contribute to structuring the community. In both years, cyanobacterial community change was strongly correlated with dissolved inorganic nitrogen (DIN) concentrations, and Aphanizomenon and Microcystis alternated dominance throughout the pre-toxic, toxic, and post-toxic phases of the lake. Microcystin concentrations increased a few days after the first significant N2 fixation rates were observed. Then, following large early summer N2 fixation events, Microcystis increased and became most abundant. Maximum microcystin concentrations coincided with Microcystis dominance. In both years, DIN concentrations dropped again in late summer, and N2 fixation rates and Aphanizomenon abundance increased before the lake mixed in

  11. Understanding the Variability in Soybean Nitrogen Fixation across Agroecosystems

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Conventional farming practices have uncoupled carbon (C) and nitrogen (N) cycles through the application of inorganic N fertilizers applied in plant available forms at levels that saturate the system. As a result, extensive N losses via leaching and denitrification are having significant environment...

  12. Increasing subtropical North Pacific Ocean nitrogen fixation since the Little Ice Age

    NASA Astrophysics Data System (ADS)

    Sherwood, Owen A.; Guilderson, Thomas P.; Batista, Fabian C.; Schiff, John T.; McCarthy, Matthew D.

    2014-01-01

    The North Pacific subtropical gyre (NPSG) plays a major part in the export of carbon and other nutrients to the deep ocean. Primary production in the NPSG has increased in recent decades despite a reduction in nutrient supply to surface waters. It is thought that this apparent paradox can be explained by a shift in plankton community structure from mostly eukaryotes to mostly nitrogen-fixing prokaryotes. It remains uncertain, however, whether the plankton community domain shift can be linked to cyclical climate variability or a long-term global warming trend. Here we analyse records of bulk and amino-acid-specific 15N/14N isotopic ratios (δ15N) preserved in the skeletons of long-lived deep-sea proteinaceous corals collected from the Hawaiian archipelago; these isotopic records serve as a proxy for the source of nitrogen-supported export production through time. We find that the recent increase in nitrogen fixation is the continuation of a much larger, centennial-scale trend. After a millennium of relatively minor fluctuation, δ15N decreases between 1850 and the present. The total shift in δ15N of -2 per mil over this period is comparable to the total change in global mean sedimentary δ15N across the Pleistocene-Holocene transition, but it is happening an order of magnitude faster. We use a steady-state model and find that the isotopic mass balance between nitrate and nitrogen fixation implies a 17 to 27 per cent increase in nitrogen fixation over this time period. A comparison with independent records suggests that the increase in nitrogen fixation might be linked to Northern Hemisphere climate change since the end of the Little Ice Age.

  13. Nitrogen fixation in a non-heterocystous cyanobacterial mat from a mountain river.

    PubMed

    Berrendero, Esther; Valiente, Eduardo Fernández; Perona, Elvira; Gómez, Claudia L; Loza, Virginia; Muñoz-Martín, M Ángeles; Mateo, Pilar

    2016-01-01

    In situ nitrogen fixation was investigated in a cyanobacterial mat growing on the bed of rocks of the Muga River, Spain. The filamentous non-heterocystous cyanobacterium Schizothrix dominated the mat, showing nitrogenase activity in the light at similar rates to those found in nearby heterocystous Rivularia colonies. N2 fixation in the light was significantly increased by an inhibitor of PSII and oxygen evolution, DCMU (3-[3,4-dichlorophenyl]-1,1-dimethylurea), and anaerobic conditions. However, no nitrogenase activity was found in the dark. Addition of fructose as a respiratory substrate induced nitrogenase activity in samples incubated under aerobic conditions in the dark but not in anaerobic conditions. Microelectrode oxygen profiles showed internal microaerobic microzones where nitrogen fixation might concentrate. Analyses of the 16S rRNA gene revealed only the presence of sequences belonging to filamentous non-heterocystous cyanobacteria. nifH gene diversity showed that the major phylotypes also belonged to this group. One of the three strains isolated from the Schizothrix mat was capable of fixing N2 and growing in the absence of combined N. This was consistent with the nifH gene analysis. These results suggest a relevant contribution of non-heterocystous cyanobacteria to nitrogen fixation in these mats. PMID:27476439

  14. Nitrogen fixation in a non-heterocystous cyanobacterial mat from a mountain river

    NASA Astrophysics Data System (ADS)

    Berrendero, Esther; Valiente, Eduardo Fernández; Perona, Elvira; Gómez, Claudia L.; Loza, Virginia; Muñoz-Martín, M. Ángeles; Mateo, Pilar

    2016-08-01

    In situ nitrogen fixation was investigated in a cyanobacterial mat growing on the bed of rocks of the Muga River, Spain. The filamentous non-heterocystous cyanobacterium Schizothrix dominated the mat, showing nitrogenase activity in the light at similar rates to those found in nearby heterocystous Rivularia colonies. N2 fixation in the light was significantly increased by an inhibitor of PSII and oxygen evolution, DCMU (3-[3,4-dichlorophenyl]-1,1-dimethylurea), and anaerobic conditions. However, no nitrogenase activity was found in the dark. Addition of fructose as a respiratory substrate induced nitrogenase activity in samples incubated under aerobic conditions in the dark but not in anaerobic conditions. Microelectrode oxygen profiles showed internal microaerobic microzones where nitrogen fixation might concentrate. Analyses of the 16S rRNA gene revealed only the presence of sequences belonging to filamentous non-heterocystous cyanobacteria. nifH gene diversity showed that the major phylotypes also belonged to this group. One of the three strains isolated from the Schizothrix mat was capable of fixing N2 and growing in the absence of combined N. This was consistent with the nifH gene analysis. These results suggest a relevant contribution of non-heterocystous cyanobacteria to nitrogen fixation in these mats.

  15. Nitrogen fixation in a non-heterocystous cyanobacterial mat from a mountain river

    PubMed Central

    Berrendero, Esther; Valiente, Eduardo Fernández; Perona, Elvira; Gómez, Claudia L.; Loza, Virginia; Muñoz-Martín, M. Ángeles; Mateo, Pilar

    2016-01-01

    In situ nitrogen fixation was investigated in a cyanobacterial mat growing on the bed of rocks of the Muga River, Spain. The filamentous non-heterocystous cyanobacterium Schizothrix dominated the mat, showing nitrogenase activity in the light at similar rates to those found in nearby heterocystous Rivularia colonies. N2 fixation in the light was significantly increased by an inhibitor of PSII and oxygen evolution, DCMU (3-[3,4-dichlorophenyl]-1,1-dimethylurea), and anaerobic conditions. However, no nitrogenase activity was found in the dark. Addition of fructose as a respiratory substrate induced nitrogenase activity in samples incubated under aerobic conditions in the dark but not in anaerobic conditions. Microelectrode oxygen profiles showed internal microaerobic microzones where nitrogen fixation might concentrate. Analyses of the 16S rRNA gene revealed only the presence of sequences belonging to filamentous non-heterocystous cyanobacteria. nifH gene diversity showed that the major phylotypes also belonged to this group. One of the three strains isolated from the Schizothrix mat was capable of fixing N2 and growing in the absence of combined N. This was consistent with the nifH gene analysis. These results suggest a relevant contribution of non-heterocystous cyanobacteria to nitrogen fixation in these mats. PMID:27476439

  16. Nitrogen fixation in sediments along a depth transect through the Peruvian oxygen minimum zone

    NASA Astrophysics Data System (ADS)

    Gier, J.; Sommer, S.; Löscher, C. R.; Dale, A. W.; Schmitz, R. A.; Treude, T.

    2015-09-01

    Benthic nitrogen (N2) fixation and sulfate reduction (SR) were investigated in the Peruvian oxygen minimum zone (OMZ). Sediment samples, retrieved by a multiple corer were taken at six stations (70-1025 m) along a depth transect at 12° S, covering anoxic and hypoxic bottom water conditions. Benthic N2 fixation was detected at all sites, with high rates measured in OMZ mid-waters between the 70 and 253 m and lowest N2 fixation rates below 253 m down to 1025 m water depth. SR rates were decreasing with increasing water depth, with highest rates at the shallow site. Benthic N2 fixation depth profiles largely overlapped with SR depth profiles, suggesting that both processes are coupled. The potential of N2 fixation by SR bacteria was verified by the molecular analysis of nifH genes. Detected nifH sequences clustered with SR bacteria that have been demonstrated to fix N2 in other benthic environments. Depth-integrated rates of N2 fixation and SR showed no direct correlation along the 12° S transect, suggesting that the benthic diazotrophs in the Peruvian OMZ are being controlled by additional various environmental factors. The organic matter availability and the presence of sulfide appear to be major drivers for benthic diazotrophy. It was further found that N2 fixation was not inhibited by high ammonium concentrations. N2 fixation rates in OMZ sediments were similar to rates measured in other organic-rich sediments. Overall, this work improves our knowledge on N sources in marine sediments and contributes to a better understanding of N cycling in OMZ sediments.

  17. Nitrogen fixation by immobilized NIF derepressed Klebsiella pneumoniae cells

    SciTech Connect

    Venkatasubramanian, K.; Toda, Y.

    1980-01-01

    In vitro production of ammonia through biological means poses a number of challenges. The organisms should be able to accumulate considerable concentrations of ammonia in the medium. Secondly, nonphotosynthetic organisms must be supplied with high-energy substrates to carry out the fixation reaction. Thirdly, the organisms must be kept in a viable state to produce ammonia over long periods of time. In this article, preliminary results on the production of ammonia by a mutant strain of Klebsiella pneumoniae in continuous reactor systems are discussed. Continuous production of ammonia becomes feasible through the immobilization of the whole microbial cells and then through the use of the resulting catalyst system in a flow-through reactor. The rationale for immobilizing microbial cells and the advantages of such an approach over traditional fermentation processes are briefly described as they relate to the microbial production of ammonia. The microbial cells can be immobilized in such a way that their viability is still maintained in the immobilized state. This, in turn, obviates addition of cofactors, which is often an expensive step associated with immobilized multi-enzyme systems. Reconstituted bovine-hide collagen as the carrier matrix for fixing the cells was the carrier of choice for our work on immobilized Klebsiella cells. Polyacrylamide gels were examined as an alternate carrier matrix but results from this were found to be inferior to those collagen immobilized cell system.

  18. Effect of Interactions Among Algae on Nitrogen Fixation by Blue-Green Algae (Cyanobacteria) in Flooded Soils

    PubMed Central

    Wilson, John T.; Greene, Sarah; Alexander, Martin

    1979-01-01

    Nitrogen fixation (C2H2 reduction) by algae in flooded soil was limited by interactions within the algal community. Nitrogen fixation by either indigenous algae or Tolypothrix tenuis was reduced severalfold by a dense suspension of the green alga Nephrocytium sp. Similarly, interactions between the nitrogen-fixing alga (cyanobacterium) Aulosira 68 and natural densities of indigenous algae limited nitrogen-fixing activity in one of two soils examined. This was demonstrated by developing a variant of Aulosira 68 that was resistant to the herbicide simetryne at concentrations that prevented development of indigenous algae. More nitrogen was fixed by the resistant variant in flooded soil containing herbicide than was fixed in herbicide-free soil by either the indigenous algae or indigenous algae plus the parent strain of Aulosira. Interference from indigenous algae may hamper the development of nitrogen-fixing algae introduced into rice fields in attempts to increase biological nitrogen fixation. PMID:16345463

  19. Diazotrophy in the Deep: An analysis of the distribution, magnitude, geochemical controls, and biological mediators of deep-sea benthic nitrogen fixation

    NASA Astrophysics Data System (ADS)

    Dekas, Anne Elizabeth

    Biological nitrogen fixation (the conversion of N2 to NH3) is a critical process in the oceans, counteracting the production of N2 gas by dissimilatory bacterial metabolisms and providing a source of bioavailable nitrogen to many nitrogen-limited ecosystems. One currently poorly studied and potentially underappreciated habitat for diazotrophic organisms is the sediments of the deep-sea. Although nitrogen fixation was once thought to be negligible in non-photosynthetically driven benthic ecosystems, the present study demonstrates the occurrence and expression of a diversity of nifH genes (those necessary for nitrogen fixation), as well as a widespread ability to fix nitrogen at high rates in these locations. The following research explores the distribution, magnitude, geochemical controls, and biological mediators of nitrogen fixation at several deep-sea sediment habitats, including active methane seeps (Mound 12, Costa Rica; Eel River Basin, CA, USA; Hydrate Ridge, OR, USA; and Monterey Canyon, CA, USA), whale-fall sites (Monterey Canyon, CA), and background deep-sea sediment (off-site Mound 12 Costa Rica, off-site Hydrate Ridge, OR, USA; and Monterey Canyon, CA, USA). The first of the five chapters describes the FISH-NanoSIMS method, which we optimized for the analysis of closely associated microbial symbionts in marine sediments. The second describes an investigation of methane seep sediment from the Eel River Basin, where we recovered nifH sequences from extracted DNA, and used FISH-NanoSIMS to identify methanotrophic archaea (ANME-2) as diazotrophs, when associated with functional sulfate-reducing bacterial symbionts. The third and fourth chapters focus on the distribution and diversity of active diazotrophs (respectively) in methane seep sediment from Mound 12, Costa Rica, using a combination of 15N-labeling experiments, FISH-NanoSIMS, and RNA and DNA analysis. The fifth chapter expands the scope of the investigation by targeting diverse samples from methane

  20. Nitrogen fixation in sediments along a depth transect through the Eastern Boundary Upwelling Systems off Peru and Mauritania

    NASA Astrophysics Data System (ADS)

    Gier, J.; Sommer, S.; Löscher, C. R.; Dale, A.; Schmitz, R. A.; Treude, T.

    2015-12-01

    The distribution of benthic nitrogen (N2) fixation and its relevance for N cycling in the Eastern Boundary Upwelling Systems (EBUS) are still unknown. Recent studies confirm that benthic N2 fixation can be coupled to sulfate reduction (SR) and that several species of sulfate reducing bacteria have the genetic ability to fix N due to the presence of the gene encoding for the nitrogenase enzyme. We investigated benthic N2 fixation and SR in the Peruvian oxygen minimum zone at 12°S and in the Mauritanian upwelling system at 18°N along a depth transect. Sediments were retrieved by a multicorer and a benthic lander at six stations in both regions. Benthic N2 fixation occurred throughout the sediment in both EBUS. Off Peru the highest integrated (0-20 cm) N2 fixation rate of 0.4 mmol N/m2/d was measured inside the core of the OMZ at 253 m water depth. Off Mauritania the highest integrated (0-20 cm) N2 fixation rate of 0.15 mmol N/m2/d was measured at 90 m, coinciding with a low bottom water oxygen concentration (30 μM). N2 fixation depth profiles often overlapped with SR activity. Moreover, sequencing data yielded insights into the composition and diversity of the nifH gene pool in EBUS sediments. Interestingly, detected sequences in both EBUS clustered with SR bacteria, such as Desulfovibrio vulgaris and several of the novel detected clades belonged to uncultured diazotrophs. Our results suggest that N2 fixation and SR were coupled to a large extent in both regions. However, potential environmental factors controlling benthic diazotrophs in the EBUS appear to be the availability of sulfide and organic matter. Additionally, no inhibition of N2 fixation at high ammonium concentrations was found, which highlights gaps in our knowledge regards the interaction between ammonium availability and diazotrophy. Our results contribute to a better understanding of N cycling in EBUS sediments and sources of fixed N.

  1. Biological invasion by Myrica faya in Hawaii: Plant demography, nitrogen fixation, ecosystem effects

    SciTech Connect

    Vitousek, P.M.; Walker, L.R. )

    1989-09-01

    Myrica faya, an introduced actinorhizal nitrogen fixer, in invading young volcanic sites in Hawaii Volcanoes National Park. We examined the population biology of the invader and ecosystem-level consequences of its invasion in open-canopied forests resulting from volcanic cinder-fall. Although Myrica faya is nominally dioecious, both males and females produce large amounts of fruit that are utilized by a number of exotic and native birds, particularly the exotic Zosterops japonica. In areas of active colonization, Myrica seed rain under perch trees of the dominant native Metrosideros polymorpha ranged from 6 to 60 seeds m{sup {minus}2} yr{sup {minus}1}; no seeds were captured in the open. Planted seeds of Myrica also germinated an established better under isolated individuals of Metrosideros than in the open. Diameter growth of Myrica is > 15-fold greater than that of Metrosideros, and the Myrica population is increasing rapidly. Rates of nitrogen fixation were measured using the acetylene reduction assay calibrated with {sup 15}N. Myrica nodules reduced acetylene at between 5 and 20 {mu}mol g{sup {minus}1} h{sup {minus}1}, a rate that extrapolated to nitrogen fixation of 18 kg ha{sup {minus}1} in a densely colonized site. By comparison, all native sources of nitrogen fixation summed to 0.2 kg ha{sup {minus}1} yr{sup {minus}1}, and precipitation added < 4 kg ha{sup {minus}1} yr{sup {minus}1}. Measurements of litter decomposition and nitrogen release, soil nitrogen mineralization, and plant growth in bioassays all demonstrated that nitrogen fixed by Myrica becomes available to other organisms as well. We conclude that biological invasion by Myrica faya alters ecosystem-level properties in this young volcanic area; at least in this case, the demography and physiology of one species controls characteristics of a whole ecosystem.

  2. Environmental Forcing of Nitrogen Fixation in the Eastern Tropical and Sub-Tropical North Atlantic Ocean

    PubMed Central

    Rijkenberg, Micha J. A.; Langlois, Rebecca J.; Mills, Matthew M.; Patey, Matthew D.; Hill, Polly G.; Nielsdóttir, Maria C.; Compton, Tanya J.; LaRoche, Julie; Achterberg, Eric P.

    2011-01-01

    During the winter of 2006 we measured nifH gene abundances, dinitrogen (N2) fixation rates and carbon fixation rates in the eastern tropical and sub-tropical North Atlantic Ocean. The dominant diazotrophic phylotypes were filamentous cyanobacteria, which may include Trichodesmium and Katagnymene, with up to 106 L−1 nifH gene copies, unicellular group A cyanobacteria with up to 105 L−1 nifH gene copies and gamma A proteobacteria with up to 104 L−1 nifH gene copies. N2 fixation rates were low and ranged between 0.032–1.28 nmol N L−1 d−1 with a mean of 0.30±0.29 nmol N L−1 d−1 (1σ, n = 65). CO2-fixation rates, representing primary production, appeared to be nitrogen limited as suggested by low dissolved inorganic nitrogen to phosphate ratios (DIN:DIP) of about 2±3.2 in surface waters. Nevertheless, N2 fixation rates contributed only 0.55±0.87% (range 0.03–5.24%) of the N required for primary production. Boosted regression trees analysis (BRT) showed that the distribution of the gamma A proteobacteria and filamentous cyanobacteria nifH genes was mainly predicted by the distribution of Prochlorococcus, Synechococcus, picoeukaryotes and heterotrophic bacteria. In addition, BRT indicated that multiple a-biotic environmental variables including nutrients DIN, dissolved organic nitrogen (DON) and DIP, trace metals like dissolved aluminum (DAl), as a proxy of dust inputs, dissolved iron (DFe) and Fe-binding ligands as well as oxygen and temperature influenced N2 fixation rates and the distribution of the dominant diazotrophic phylotypes. Our results suggest that lower predicted oxygen concentrations and higher temperatures due to climate warming may increase N2 fixation rates. However, the balance between a decreased supply of DIP and DFe from deep waters as a result of more pronounced stratification and an enhanced supply of these nutrients with a predicted increase in deposition of Saharan dust may ultimately determine the consequences of climate

  3. [Nitrogen fixation potential of biological soil crusts in Heidaigou open coal mine, Inner Mongolia, China].

    PubMed

    Zhang, Peng; Huang, Lei; Hu, Yi-gang; Zhao, Yang; Wu, Yong-chen

    2016-02-01

    Nitrogen limitation is common in terrestrial ecosystems, and it is particularly severe in damaged ecosystems in arid regions. Biological soil crusts (BSCs) , as a crucial component of recovered vegetation, play a vital role in nitrogen fixation during the ecological restoration processes of damaged ecosystems in arid and semi-arid regions. In this study, two dominant types of BSCs (i.e., cyanobacterial-algal crusts and moss crusts) that are widely distributed in the re-vegetated area of Heidaigou open pit coal mine were investigated. Samples were collected in the field and their nitrogenase activities (NA) were measured in the laboratory. The responses of NA to different hydro-thermal factors and the relationships between NA and herbs in addition to crust coverage were analyzed. The results indicated that BSCs under reconstructed vegetation at different succession stages, abandoned land and natural vegetation showed values of NA ranging from 9 to 150 µmol C2H4 . m-2 . h-1, and the NA value of algae crust (77 µmol C2H4 . m-2 . h-1) was markedly higher than that of moss crust (17 µmol C2H4 . m-2 . h-1). In the re-vegetated area, cyanobacterial-algal crust and moss crust under shrub-herb had higher NA values than those of crusts under arbor-shrnb and arbor-shrub-herb. The relationship between NA of the two BSCs and soil relative water content (10% - 100%) as well as culture temperature (5-45 °C) were of quadratic function. With elevated water content and cultural temperature, the NA values increased at the initial stage and then decreased, and reached the maximum value at 25 °C of cultural temperature and 60% or 80% of relative water content. The NA of cyanobacterial-algal crust had a significant quadratic function with herb coverage, as NA declined when herb coverage was higher than 20%. A significant negative correlation was observed between the NA of moss crusts and herb coverage. The NA values of the two types of BSCs had a significant positive correlation

  4. Increasing Nitrogen Fixation and Seed Development in Soybean Requires Complex Adjustments of Nodule Nitrogen Metabolism and Partitioning Processes.

    PubMed

    Carter, Amanda M; Tegeder, Mechthild

    2016-08-01

    Legumes are able to access atmospheric di-nitrogen (N2) through a symbiotic relationship with rhizobia that reside within root nodules. In soybean, following N2 fixation by the bacteroids, ammonia is finally reduced in uninfected cells to allantoin and allantoic acid [1]. These ureides present the primary long-distance transport forms of nitrogen (N), and are exported from nodules via the xylem for shoot N supply. Transport of allantoin and allantoic acid out of nodules requires the function of ureide permeases (UPS1) located in cells adjacent to the vasculature [2, 3]. We expressed a common bean UPS1 transporter in cortex and endodermis cells of soybean nodules and found that delivery of N from nodules to shoot, as well as seed set, was significantly increased. In addition, the number of transgenic nodules was increased and symbiotic N2 fixation per nodule was elevated, indicating that transporter function in nodule N export is a limiting step in bacterial N acquisition. Further, the transgenic nodules showed considerable increases in nodule N assimilation, ureide synthesis, and metabolite levels. This suggests complex adjustments of nodule N metabolism and partitioning processes in support of symbiotic N2 fixation. We propose that the transgenic UPS1 plants display metabolic and allocation plasticity to overcome N2 fixation and seed yield limitations. Overall, it is demonstrated that transporter function in N export from nodules is a key step for enhancing atmospheric N2 fixation and nodule function and for improving shoot N nutrition and seed development in legumes. PMID:27451897

  5. Data-based assessment of environmental controls on global marine nitrogen fixation

    NASA Astrophysics Data System (ADS)

    Luo, Y.-W.; Lima, I. D.; Karl, D. M.; Doney, S. C.

    2013-04-01

    There are a number of hypotheses for the environmental controls on marine nitrogen fixation (NF). Most of these hypotheses have not been assessed against direct measurements on the global scale. In this study, we use ~ 500 depth-integrated field measurements of NF covering the Pacific and Atlantic Oceans to test whether the spatial variance of these measurements can be explained by the commonly hypothesized environmental controls, including measurement-based surface solar radiation, mixed layer depth, sea surface temperature, surface nitrate and phosphate concentrations, surface excess phosphate (P*), atmospheric dust deposition and surface wind speed, as well as minimum dissolved oxygen in upper 500 m to identify possible subsurface denitrification zones. By conducting simple linear regression and stepwise multiple linear regression (MLR) analyses, solar radiation and/or sea surface temperature as well as subsurface dissolved oxygen are identified as the predictors explaining the most spatial variance in the observed NF data, while dust deposition and wind speed do not appear to influence the spatial patterns of NF on global scale. Our study suggests that marine NF is coupled to regional loss of fixed nitrogen induced by subsurface low oxygen concentration, with its magnitude constrained by solar radiation or temperature. By applying the MLR-derived equation, we estimate the global-integrated NF at 71 (error range 49-104) Tg N yr-1 in the open ocean, acknowledging that it could be substantially higher as the 15N2-assimilation method used by most of the field samples underestimates NF. Our conclusion suggests that marine NF will increase in the future if subsurface nitrogen-losses increase as a consequence of developing deoxygenation with the global warming, a projection that will be modulated by other factors such as warming, elevated carbon dioxide, and changes in macro- and micro-nutrient distributions. More field NF samples in the Pacific and Indian Oceans

  6. Growth, nitrogen fixation, yield and kernel quality of peanut in response to lime, organic and inorganic fertilizer levels.

    PubMed

    Basu, Manisha; Bhadoria, P B S; Mahapatra, S C

    2008-07-01

    The aim of this investigation was to study the effect of different levels of chemical fertilizers alone and in combination with farmyard manure and lime on growth, nitrogen fixation, yield and kernel quality of peanut in an acid lateritic soil. Five fertilization levels viz., no chemical fertilizer (CF) (F0), CF @ 20:40:30 (F1), CF @ 40:80:60 (F2) kg ha(-1) NPK, F1 +2.5 t ha(-1) FYM (F3) and F2 +5 t ha(-1) FYM (F4) with and without liming (2 t ha(-1)) were tested. Results revealed that integrated application of FYM+CF at F3 level significantly (P0.05) improved the nitrogen content of nodules (12.4%), kernel yield (19.3%), mineral composition, oil content (4.8%), protein content (28.2%) and hydration coefficient (11.6%) of kernels over sole CF at F1 level. Maximum level of CF or FYM+CF though improved the population of symbiotic nitrogen fixing bacteria in the peanut rhizosphere, however, could not improve nitrogen fixation, yield and kernel quality. PMID:17993273

  7. Nitrogen fixation by photosynthetic bacteria in lowland rice culture.

    PubMed

    Habte, M; Alexander, M

    1980-02-01

    Propanil (3',4'-dichloropropionanilide) was a potent inhibitor of the nitrogenase activity of blue-green algae (cyanobacteria) in flooded soil, but the herbicide at comparable concentrations was not toxic to rice, protozoa, and nitrogen-fixing bacteria. Ethanol-amended flooded soils treated with propanil exhibited higher rates of nitrogenase activity than those not treated with the herbicide. The enhanced nitrogenase activity in propanil-treated soils was associated with a rise in the population of purple sulfur bacteria, especially of cells resembling Chromatium and Thiospirillum. By employing propanil and a means of excluding light from the floodwater to prevent the development of phototrophs during rice growth under lowland conditions, the relative activities of blue-green algae, photosynthetic bacteria, and the rhizosphere microflora were determined. The results suggest that the potential contribution of photosynthetic bacteria may be quite high. PMID:16345507

  8. Nitrogen Fixation by Photosynthetic Bacteria in Lowland Rice Culture

    PubMed Central

    Habte, M.; Alexander, M.

    1980-01-01

    Propanil (3′,4′-dichloropropionanilide) was a potent inhibitor of the nitrogenase activity of blue-green algae (cyanobacteria) in flooded soil, but the herbicide at comparable concentrations was not toxic to rice, protozoa, and nitrogen-fixing bacteria. Ethanol-amended flooded soils treated with propanil exhibited higher rates of nitrogenase activity than those not treated with the herbicide. The enhanced nitrogenase activity in propanil-treated soils was associated with a rise in the population of purple sulfur bacteria, especially of cells resembling Chromatium and Thiospirillum. By employing propanil and a means of excluding light from the floodwater to prevent the development of phototrophs during rice growth under lowland conditions, the relative activities of blue-green algae, photosynthetic bacteria, and the rhizosphere microflora were determined. The results suggest that the potential contribution of photosynthetic bacteria may be quite high. PMID:16345507

  9. Correlation between nitrogen fixation rate and alginate productivity of an indigenous Azotobacter vinelandii from Iran

    PubMed Central

    Nosrati, R; Owlia, P; Saderi, H; Olamaee, M; Rasooli, I; Akhavian, Tehrani A

    2012-01-01

    Background and Objectives Azotobacter vinelandii, a gamma-proteobacterium, is an obligate aerobic free-living gram-negative soil bacterium capable of fixing nitrogen. Oxygen transfer rate into the cell is reduced by the increase of alginate concentrations during the course of A. vinelandii cultivation. This phenomenon provides a low intracellular oxygen concentration needed for nitrogenase activity. The aim of this study was to design a simple strategy to explain the alginate production, cell growth and nitrogenase activity correlation in A. vinelandii under aerobic conditions. Material and Methods Thirty-five different soil samples were taken from the rhizosphere of agricultural crops of Iran. Enrichment and isolation strategies were employed for microbial isolation. Physiological and biochemical characteristics were determined. Molecular identification was performed using selective nifH-g1 primers. Alginate production and nitrogenase activity assay by each isolate of Azotobacter were carried out. Bacterial growth, alginate production and Nitrogenase activity were conducted by time-coursed quantitative measurements. Results Total of 26 isolates were selected after enrichment, isolation, and screening. The isolate was identified by molecular tests as A. vinelandii. The highest alginate productions of 1.02 g/l and 0.91g/l were noted after 4 days in 8 isolates, cell biomass of which were estimated 4.88-5.26 g/l. Six of 8 isolates were able to fix atmospheric N2 on nitrogen-free medium. Rates obtained in isolates were in the range of 12.1 to 326.4 nmol C2H4 h-1 vial-1. Conclusions Nitrogen fixation and alginate production yielded significant and positive Pearson's correlation coefficient of R2 = 0.760, p ∼ 0.02. Finally association between bacterial growth, alginate production and nitrogenase activity almost noticeable yielded significant and positive Pearson's correlation coefficient R2= 0.723, p ∼ 0.04. PMID:23066492

  10. Nodule and Leaf Nitrate Reductases and Nitrogen Fixation in Medicago sativa L. under Water Stress

    PubMed Central

    Aparicio-Tejo, P.; Sánchez-Díaz, Manuel

    1982-01-01

    The effect of water stress on patterns of nitrate reductase activity in the leaves and nodules and on nitrogen fixation were investigated in Medicago sativa L. plants watered 1 week before drought with or without NO3−. Nitrogen fixation was decreased by water stress and also inhibited strongly by the presence of NO3−. During drought, leaf nitrate reductase activity (NRA) decreased significantly particularly in plants watered with NO3−, while with rewatering, leaf NRA recovery was quite important especially in the NO3−-watered plants. As water stress progressed, the nodular NRA increased both in plants watered with NO3− and in those without NO3− contrary to the behavior of the leaves. Beyond −15.105 pascal, nodular NRA began to decrease in plants watered with NO3−. This phenomenon was not observed in nodules of plants given water only. Upon rewatering, it was observed that in plants watered with NO3− the nodular NRA increased again, while in plants watered but not given NO3−, such activity began to decrease. Nitrogen fixation increased only in plants without NO3−. PMID:16662233

  11. Dinitrogen fixation and dissolved organic nitrogen fueled primary production and particulate export during the VAHINE mesocosm experiment (New Caledonia lagoon)

    NASA Astrophysics Data System (ADS)

    Berthelot, H.; Moutin, T.; L'Helguen, S.; Leblanc, K.; Hélias, S.; Grosso, O.; Leblond, N.; Charrière, B.; Bonnet, S.

    2015-07-01

    In the oligotrophic ocean characterized by nitrate (NO3-) depletion in surface waters, dinitrogen (N2) fixation and dissolved organic nitrogen (DON) can represent significant nitrogen (N) sources for the ecosystem. In this study, we deployed large in situ mesocosms in New Caledonia in order to investigate (1) the contribution of N2 fixation and DON use to primary production (PP) and particle export and (2) the fate of the freshly produced particulate organic N (PON), i.e., whether it is preferentially accumulated and recycled in the water column or exported out of the system. The mesocosms were fertilized with phosphate (PO43-) in order to prevent phosphorus (P) limitation and promote N2 fixation. The diazotrophic community was dominated by diatom-diazotroph associations (DDAs) during the first part of the experiment for 10 days (P1) followed by the unicellular N2-fixing cyanobacteria UCYN-C for the last 9 days (P2) of the experiment. N2 fixation rates averaged 9.8 ± 4.0 and 27.7 ± 8.6 nmol L-1 d-1 during P1 and P2, respectively. NO3- concentrations (< 0.04 μmol L-1) in the mesocosms were a negligible source of N, indicating that N2 fixation was the main driver of new production throughout the experiment. The contribution of N2 fixation to PP was not significantly different (p > 0.05) during P1 (9.0 ± 3.3 %) and P2 (12.6 ± 6.1 %). However, the e ratio that quantifies the efficiency of a system to export particulate organic carbon (POCexport) compared to PP (e ratio = POCexport/PP) was significantly higher (p < 0.05) during P2 (39.7 ± 24.9 %) than during P1 (23.9 ± 20.2 %), indicating that the production sustained by UCYN-C was more efficient at promoting C export than the production sustained by DDAs. During P1, PON was stable and the total amount of N provided by N2 fixation (0.10 ± 0.02 μmol L-1) was not significantly different (p > 0.05) from the total amount of PON exported (0.10 ± 0.04 μmol L-1), suggesting a rapid and probably direct export of the

  12. On the influence of "non-Redfield" dissolved organic nutrient dynamics on the spatial distribution of N2 fixation and the size of the marine fixed nitrogen inventory

    NASA Astrophysics Data System (ADS)

    Somes, Christopher J.; Oschlies, Andreas

    2015-07-01

    Dissolved organic nitrogen (DON) and phosphorus (DOP) represent the most abundant form of their respective nutrient pool in the surface layer of the oligotrophic oceans and play an important role in nutrient cycling and productivity. Since DOP is generally more labile than DON, it provides additional P that may stimulate growth of nitrogen-fixing diazotrophs that supply fixed nitrogen to balance denitrification in the ocean. In this study, we introduce semirecalcitrant components of DON and DOP as state variables in an existing global ocean-atmosphere-sea ice-biogeochemistry model of intermediate complexity to assess their impact on the spatial distribution of nitrogen fixation and the size of the marine fixed nitrogen inventory. Large-scale surface data sets of global DON and Atlantic Ocean DOP are used to constrain the model. Our simulations suggest that both preferential DOP remineralization and phytoplankton DOP uptake are important "non-Redfield" processes (i.e., deviate from molar N:P = 16) that need to be accounted for to explain the observed patterns of DOP. Additional non-Redfield DOP sensitivity experiments testing dissolved organic matter (DOM) production rate uncertainties that best reproduce the observed spatial patterns of DON and DOP stimulate additional nitrogen fixation that increases the size of the global marine fixed nitrogen inventory by 4.7 ± 1.7% compared to the simulation assuming Redfield DOM stoichiometry that underestimates the observed nitrogen inventory. The extra 8 Tg yr-1 of nitrogen fixation stimulated in the Atlantic Ocean is mainly responsible for this increase due to its large spatial separation from water column denitrification, which buffers any potential nitrogen surplus in the Pacific Ocean. Our study suggests that the marine fixed nitrogen budget is sensitive to non-Redfield DOP dynamics because access to the relatively labile DOP pool expands the ecological niche for nitrogen-fixing diazotrophs.

  13. Potential for Nitrogen Fixation and Nitrification in the Granite-Hosted Subsurface at Henderson Mine, CO

    PubMed Central

    Swanner, Elizabeth D.; Templeton, Alexis S.

    2011-01-01

    The existence of life in the deep terrestrial subsurface is established, yet few studies have investigated the origin of nitrogen that supports deep life. Previously, 16S rRNA gene surveys cataloged a diverse microbial community in subsurface fluids draining from boreholes 3000 feet deep at Henderson Mine, CO, USA (Sahl et al., 2008). The prior characterization of the fluid chemistry and microbial community forms the basis for the further investigation here of the source of NH4+. The reported fluid chemistry included N2, NH4+ (5–112 μM), NO2− (27–48 μM), and NO3− (17–72 μM). In this study, the correlation between low NH4+ concentrations in dominantly meteoric fluids and higher NH4+ in rock-reacted fluids is used to hypothesize that NH4+ is sourced from NH4+-bearing biotite. However, biotite samples from the host rocks and ore-body minerals were analyzed by Fourier transform infrared (FTIR) microscopy and none-contained NH4+. However, the nitrogenase-encoding gene nifH was successfully amplified from DNA of the fluid sample with high NH4+, suggesting that subsurface microbes have the capability to fix N2. If so, unregulated nitrogen fixation may account for the relatively high NH4+ concentrations in the fluids. Additionally, the amoA and nxrB genes for archaeal ammonium monooxygenase and nitrite oxidoreductase, respectively, were amplified from the high NH4+ fluid DNA, while bacterial amoA genes were not. Putative nitrifying organisms are closely related to ammonium-oxidizing Crenarchaeota and nitrite-oxidizing Nitrospira detected in other subsurface sites based upon 16S rRNA sequence analysis. Thermodynamic calculations underscore the importance of NH4+ as an energy source in a subsurface nitrification pathway. These results suggest that the subsurface microbial community at Henderson is adapted to the low nutrient and energy environment by their capability of fixing nitrogen, and that fixed nitrogen may support subsurface biomass via

  14. Primary productivity and nitrogen fixation by Trichodesmium spp. in the Arabian Sea

    NASA Astrophysics Data System (ADS)

    Parab, Sushma G.; Matondkar, S. G. P.

    2012-12-01

    Trichodesmium was studied with the purpose of understanding its distribution, organic production and nitrogen fixation in the Arabian Sea. Out of the 143 stations sampled, a total of 93 stations showed the presence of Trichodesmium filaments. Two species of Trichodesmium namely, T. thiebautii and T. erythraeum were found. These were distributed on the basis of the physico-chemical conditions of the Arabian Sea. This was the first time that we managed to detect and record the presence of Trichodesmium thiebautii bloom in the Arabian Sea at depths as deep as 60-70 m. Total counts of Trichodesmium varied between 0 and 400737 filamentsL- 1. T. thiebautii developed in offshore waters during the fall intermonsoon, when the water temperature was around 28 °C and nitrate content was as low as 0.34 μM. After the northeast monsoon, Trichodesmium erythraeum developed in the offshore area and then spread to coastal waters. Both species of Trichodesmium together produced a total of 0.263 TgCyear- 1 and fixed a total of 0.2976 TgNyear- 1 in the Arabian Sea. The study revealed that Trichodesmium was a major contributor to the organic matter productivity of the Arabian Sea during the period from November to April. The seasonality of the blooms of Trichodesmium is discussed with the help of Ocean Color Monitoring (OCM) data and biogeochemical implication of these findings in the Arabian Sea.

  15. Quantifying the effect of fire disturbance on free-living nitrogen fixation in tropical ecosystems

    NASA Astrophysics Data System (ADS)

    De Oliveira Bomfim, B.; Silva, L. C. R.; Marimon-Junior, B. H.; Marimon, B.; Horwath, W. R.; Neves, L.

    2015-12-01

    Tropical forests and savannas are among the most important biomes on Earth, supporting more than half of all plant and animal species on the planet. Despite growing interest in biogeochemical processes that affect tropical forest dynamics, many, including biological nitrogen fixation (BNF), are still poorly understood. Free-living N-fixers are thought to play a key role in tropical ecosystems, alleviating N and P limitation, supporting above and below ground biomass production, as well as carbon storage in plants and soil, but this influence has yet to be quantified. Of particular interest, the spatial distribution and identity of free-living BNF under disturbance regimes that commonly lead to the conversion of forests to savannas is currently unknown. To address this critical gap in knowledge, we measured free-living BNF quantifying rates of N fixation under contrasting fire regimes in the Amazon-Cerrado transition of central Brazil. Samples were collected in 4 ha of floodable forests affected by fire and 1 ha of unburned (seasonally flooded) forest located at the Araguaia State Park, Mato Grosso State, Brazil. Free-living N-fixation rates were measured by both 15N2 (98 atom% 15N) and acethylene reduction assay (ARA). Samples were incubated in the field and left in the dark at room temperature for 12 hours. In the next few weeks we will quantify N fixation rates that will be presented in the upcoming AGU meeting.

  16. Nitrogen Fixation By Sulfate-Reducing Bacteria in Coastal and Deep-Sea Sediments

    NASA Astrophysics Data System (ADS)

    Bertics, V. J.; Löscher, C.; Salonen, I.; Schmitz-Streit, R.; Lavik, G.; Kuypers, M. M.; Treude, T.

    2011-12-01

    Sulfate-reducing bacteria (SRB) can greatly impact benthic nitrogen (N) cycling, by for instance inhibiting coupled denitrification-nitrification through the production of sulfide or by increasing the availability of fixed N in the sediment via dinitrogen (N2)-fixation. Here, we explored several coastal and deep-sea benthic habitats within the Atlantic Ocean and Baltic Sea, for the occurrence of N2-fixation mediated by SRB. A combination of different methods including microbial rate measurements of N2-fixation and sulfate reduction, geochemical analyses (porewater nutrient profiles, mass spectrometry), and molecular analyses (CARD-FISH, HISH-SIMS, "nested" PCR, and QPCR) were applied to quantify and identify the responsible processes and organisms, respectively. Furthermore, we looked deeper into the question of whether the observed nitrogenase activity was associated with the final incorporation of N into microbial biomass or whether the enzyme activity served another purpose. At the AGU Fall Meeting, we will present and compare data from numerous stations with different water depths, temperatures, and latitudes, as well as differences in key geochemical parameters, such as organic carbon content and oxygen availability. Current metabolic and molecular data indicate that N2-fixation is occurring in many of these benthic environments and that a large part of this activity may linked to SRB.

  17. BMAA Inhibits Nitrogen Fixation in the Cyanobacterium Nostoc sp. PCC 7120

    PubMed Central

    Berntzon, Lotta; Erasmie, Sven; Celepli, Narin; Eriksson, Johan; Rasmussen, Ulla; Bergman, Birgitta

    2013-01-01

    Cyanobacteria produce a range of secondary metabolites, one being the neurotoxic non-protein amino acid β-N-methylamino-L-alanine (BMAA), proposed to be a causative agent of human neurodegeneration. As for most cyanotoxins, the function of BMAA in cyanobacteria is unknown. Here, we examined the effects of BMAA on the physiology of the filamentous nitrogen-fixing cyanobacterium Nostoc sp. PCC 7120. Our data show that exogenously applied BMAA rapidly inhibits nitrogenase activity (acetylene reduction assay), even at micromolar concentrations, and that the inhibition was considerably more severe than that induced by combined nitrogen sources and most other amino acids. BMAA also caused growth arrest and massive cellular glycogen accumulation, as observed by electron microscopy. With nitrogen fixation being a process highly sensitive to oxygen species we propose that the BMAA effects found here may be related to the production of reactive oxygen species, as reported for other organisms. PMID:23966039

  18. BMAA inhibits nitrogen fixation in the cyanobacterium Nostoc sp. PCC 7120.

    PubMed

    Berntzon, Lotta; Erasmie, Sven; Celepli, Narin; Eriksson, Johan; Rasmussen, Ulla; Bergman, Birgitta

    2013-08-01

    Cyanobacteria produce a range of secondary metabolites, one being the neurotoxic non-protein amino acid β-N-methylamino-L-alanine (BMAA), proposed to be a causative agent of human neurodegeneration. As for most cyanotoxins, the function of BMAA in cyanobacteria is unknown. Here, we examined the effects of BMAA on the physiology of the filamentous nitrogen-fixing cyanobacterium Nostoc sp. PCC 7120. Our data show that exogenously applied BMAA rapidly inhibits nitrogenase activity (acetylene reduction assay), even at micromolar concentrations, and that the inhibition was considerably more severe than that induced by combined nitrogen sources and most other amino acids. BMAA also caused growth arrest and massive cellular glycogen accumulation, as observed by electron microscopy. With nitrogen fixation being a process highly sensitive to oxygen species we propose that the BMAA effects found here may be related to the production of reactive oxygen species, as reported for other organisms. PMID:23966039

  19. Glutamine synthetase mutations which affect expression of nitrogen fixation genes in Klebsiella pneumoniae.

    PubMed Central

    Ausubel, F M; Bird, S C; Durbin, K J; Janssen, K A; Margolskee, R F; Peskin, A P

    1979-01-01

    Previous studies have implicated glutamine synthetase (L-glutamate:ammonia ligase [adenosine diphosphate for-ing], EC 6.6.1.2) as a major controlling element of the nitrogen fixation (nif) genes in Klebsiella pneumoniae. We report here the isolation of a new class of K. pneumoniae mutants which exhibit altered patterns of nif and hut (histidine utlization) regulation. The expression of nif in these mutants, which were isolated as Gln+ (glutamine nonrequiring) revertants of a particular glnA mutation, is extremely sensitive to ammonia repression. These mutants have a Nif- Hut- phenotype at external ammonia concentrations at which wild-type strains are Nif+ Hut+. On the other hand, these mutants can be fully derepressed for nif at very low ammonia concentrations. We adopted the nomenclature "GlnR- (Nif- Hut-)" to facilitate discussion of the phenotype of these mutant strains. The mutations in these strains which confer the GlnR- phenotype map at or near glnA, the structural gene for glutamine synthetase. PMID:40960

  20. Nitrogen fixation in microbial mat and stromatolite communities from Cuatro Cienegas, Mexico.

    PubMed

    Falcón, L I; Cerritos, R; Eguiarte, L E; Souza, V

    2007-08-01

    Nitrogen fixation (nitrogenase activity, NA) of a microbial mat and a living stromatolite from Cuatro Cienegas, Mexico, was examined over spring, summer, and winter of 2004. The goal of the study was to characterize the diazotrophic community through molecular analysis of the nifH gene and using inhibitors of sulfate reduction and oxygenic and anoxygenic photosynthesis. We also evaluated the role of ultraviolet radiation on the diazotrophic activity of the microbial communities. Both microbial communities showed patterns of NA with maximum rates during the day that decreased significantly with 3-3,4-dichlorophenyl-1',1'-dimethylurea, suggesting the potential importance of heterocystous cyanobacteria. There is also evidence of NA by sulfur-reducing bacteria in both microbial communities suggested by the negative effect exerted by the addition of sodium molybdate. Elimination of infrared and ultraviolet radiation had no effect on NA. Both microbial communities had nifH sequences that related to group I, including cyanobacteria and purple sulfur and nonsulfur bacteria, as well as group II nitrogenases, including sulfur reducing and green sulfur bacteria. PMID:17450393

  1. The Genetics of Symbiotic Nitrogen Fixation: Comparative Genomics of 14 Rhizobia Strains by Resolution of Protein Clusters

    PubMed Central

    Black, Michael; Moolhuijzen, Paula; Chapman, Brett; Barrero, Roberto; Howieson, John; Hungria, Mariangela; Bellgard, Matthew

    2012-01-01

    The symbiotic relationship between legumes and nitrogen fixing bacteria is critical for agriculture, as it may have profound impacts on lowering costs for farmers, on land sustainability, on soil quality, and on mitigation of greenhouse gas emissions. However, despite the importance of the symbioses to the global nitrogen cycling balance, very few rhizobial genomes have been sequenced so far, although there are some ongoing efforts in sequencing elite strains. In this study, the genomes of fourteen selected strains of the order Rhizobiales, all previously fully sequenced and annotated, were compared to assess differences between the strains and to investigate the feasibility of defining a core ‘symbiome’—the essential genes required by all rhizobia for nodulation and nitrogen fixation. Comparison of these whole genomes has revealed valuable information, such as several events of lateral gene transfer, particularly in the symbiotic plasmids and genomic islands that have contributed to a better understanding of the evolution of contrasting symbioses. Unique genes were also identified, as well as omissions of symbiotic genes that were expected to be found. Protein comparisons have also allowed the identification of a variety of similarities and differences in several groups of genes, including those involved in nodulation, nitrogen fixation, production of exopolysaccharides, Type I to Type VI secretion systems, among others, and identifying some key genes that could be related to host specificity and/or a better saprophytic ability. However, while several significant differences in the type and number of proteins were observed, the evidence presented suggests no simple core symbiome exists. A more abstract systems biology concept of nitrogen fixing symbiosis may be required. The results have also highlighted that comparative genomics represents a valuable tool for capturing specificities and generalities of each genome. PMID:24704847

  2. The abiotic fixation of nitrogen on mars and other terrestrial planets: conversion of nitrogen, through NO, into nitrate, nitrite, ammonia, and nitrous oxide.

    NASA Astrophysics Data System (ADS)

    Summers, David; Basa, Ranor; Khare, Bishun; Rodoni, David

    The abiotic fixation of nitrogen is critical to understanding habitability, planetary evolution and the potential origin of life on terrestrial planets such as Mars. A non-biological source of biochemically accessible nitrogen is necessary for the origin and early evolution of life. The Martian surface has become uninhabitable, in part due to loss of atmospheric gases, such as nitrogen, resulting in an incapacity to sustain liquid surface water. Chemical sequestration in the crust is one possible mechanism for such loss. The products of nitrogen fixation also impact the climate and geochemistry of the planet. Shock heating of a non-reducing atmosphere will produce NO. This process has been well studied. We have been experimentally studying the pathways possible from NO to more stable forms in the atmosphere and crust. Our work has observed that there are multiple pathways for the fixation. One pathway observed is consistent with the theoretically predicted route via photochemical formation of HNO. Inter-estingly, this pathway is coupled to the formation of formaldehyde from CO. With liquid water, this pathway leads to nitrate and nitrite. In the presence of just water vapor, HNO appears to mostly dimerize to form N2 O. A second pathway involves the formation of NO2 from CO2 and NO. This pathway becomes more dominant without water, but the reaction of NO2 with any form of water, even just adsorbed water, can lead to nitric acid. Finally, with FeS suspended in liquid water, the direct reduction of NO to ammonia is observed. This last pathway represents the most efficient way to reduced nitrogen, with product yields in excess of 50 % in a single step. In conjunction with the reduction of NO, there is also a catalytic disproportionation at the mineral surface, converting NO to NO2 and N2 O, providing an abiotic source of nitrous oxide. This chemistry has implications for a number epochs in Martian history. For example, chemistry in the presence of water is relevant to

  3. Nitrogen fixation and metabolism by groundwater-dependent perennial plants in a hyperarid desert.

    PubMed

    Arndt, Stefan K; Kahmen, Ansgar; Arampatsis, Christina; Popp, Marianne; Adams, Mark

    2004-11-01

    The Central Asian Taklamakan desert is characterized by a hyperarid climate with less than 50 mm annual precipitation but a permanent shallow groundwater table. The perched groundwater (2-16 m) could present a reliable and constant source of nitrogen throughout the growing season and help overcome temporal nitrogen limitations that are common in arid environments. We investigated the importance of groundwater and nitrogen fixation in the nitrogen metabolism of desert plants by assessing the possible forms and availability of soil N and atmospheric N and the seasonal variation in concentration as well as isotopic composition of plant N. Water availability was experimentally modified in the desert foreland through simulated flooding to estimate the contribution of surface water and temporally increased soil moisture for nutrient uptake and plant-water relations. The natural vegetation of the Taklamakan desert is dominated by plants with high foliar nitrogen concentrations (2-3% DM) and leaf nitrate reductase activity (NRA) (0.2-1 micromol NO2- g(-1) FW h(-1)). There is little evidence that nitrogen is a limiting resource as all perennial plants exhibited fast rates of growth. The extremely dry soil conditions preclude all but minor contributions of soil N to total plant N so that groundwater is suggested as the dominant source of N with concentrations of 100 microM NO3-. Flood irrigation had little beneficial effect on nitrogen metabolism and growth, further confirming the dependence on groundwater. Nitrogen fixation was determined by the 15N natural abundance method and was a significant component of the N-requirement of the legume Alhagi, the average contribution of biologically fixed nitrogen in Alhagi was 54.8%. But nitrogen fixing plants had little ecological advantage owing to the more or less constant supply of N available from groundwater. From our data we conclude that the perennial species investigated have adapted to the environmental conditions through

  4. Nitrogen Fixation Mutants of Medicago truncatula Fail to Support Plant and Bacterial Symbiotic Gene Expression1[W][OA

    PubMed Central

    Starker, Colby G.; Parra-Colmenares, Adriana L.; Smith, Lucinda; Mitra, Raka M.; Long, Sharon R.

    2006-01-01

    The Rhizobium-legume symbiosis culminates in the exchange of nutrients in the root nodule. Bacteria within the nodule reduce molecular nitrogen for plant use and plants provide bacteria with carbon-containing compounds. Following the initial signaling events that lead to plant infection, little is known about the plant requirements for establishment and maintenance of the symbiosis. We screened 44,000 M2 plants from fast neutron-irradiated Medicago truncatula seeds and isolated eight independent mutant lines that are defective in nitrogen fixation. The eight mutants are monogenic and represent seven complementation groups. To monitor bacterial status in mutant nodules, we assayed Sinorhizobium meliloti symbiosis gene promoters (nodF, exoY, bacA, and nifH) in the defective in nitrogen fixation mutants. Additionally, we used an Affymetrix oligonucleotide microarray to monitor gene expression changes in wild-type and three mutant plants during the nodulation process. These analyses suggest the mutants can be separated into three classes: one class that supports little to no nitrogen fixation and minimal bacterial expression of nifH; another class that supports no nitrogen fixation and minimal bacterial expression of nodF, bacA, and nifH; and a final class that supports low levels of both nitrogen fixation and bacterial nifH expression. PMID:16407449

  5. Nitrogen fixation in moss-cyanobacteria associations in boreal forest ecosystems

    NASA Astrophysics Data System (ADS)

    Rousk, Kathrin

    2014-05-01

    Nitrogen (N) limits the productivity in boreal forests. A major source of 'new' N for these forests is the fixation of atmospheric N2 preformed by cyanobacteria living in association with mosses and lichens. Mosses are a dominant feature in boreal forests, accounting for 60-90% of the groundcover in pristine boreal forests and have been found to be colonized by several N2-fixing cyanobacteria. Given the ubiquitous nature of mosses in these forests, their association with N2-fixing cyanobacteria could characterize the N cycle in these ecosystems. For instance, the feather moss Pleurozium schreberi with its associated cyanobacteria fixes 1-2 kg N ha-1 yr-1, which equals the amount that enters northern boreal forests via atmospheric N deposition. Nitrogen fixation in moss-cyanobacteria associations is affected by numerous abiotic factors that could modulate the N input to the system via the moss-cyanobacteria pathway. For instance, high N availability and dry conditions inhibit N2 fixation in moss-cyanobacteria associations while phosphorus availability and moist conditions promote N2 fixation. Further, N2fixation in moss-cyanobacteria associations is resilient, and can recover from increased N inputs (12 - 15 kg N ha-1 yr-1) as well as from drought stress (moss < 9% field moisture) upon removal of these stressors. Nevertheless, the question as to how important the N2 fixing capability of moss-cyanobacteria associations is as a source of 'new' N for the N cycle in boreal forests remains. For instance, mosses can retain acquired N over long periods of time (> 1 year) and the transfer of N from moss to soil in the short-term has so far only been shown to occur after disturbances (e.g. drying rewetting events, fires). I will present results from laboratory as well as field experiments aimed to elucidate the role moss-cyanobacteria associations play for the N cycle in boreal forests and how abiotic factors control the fixation of atmospheric N2.

  6. Multifaceted Investigation of Metabolites During Nitrogen Fixation in Medicago via High Resolution MALDI-MS Imaging and ESI-MS

    NASA Astrophysics Data System (ADS)

    Gemperline, Erin; Jayaraman, Dhileepkumar; Maeda, Junko; Ané, Jean-Michel; Li, Lingjun

    2015-01-01

    Legumes have developed the unique ability to establish a symbiotic relationship with soil bacteria known as rhizobia. This interaction results in the formation of root nodules in which rhizobia thrive and reduce atmospheric dinitrogen into plant-usable ammonium through biological nitrogen fixation (BNF). Owing to the availability of genetic information for both of the symbiotic partners, the Medicago truncatula- Sinorhizobium meliloti association is an excellent model for examining the BNF process. Although metabolites are important in this symbiotic association, few studies have investigated the array of metabolites that influence this process. Of these studies, most target only a few specific metabolites, the roles of which are either well known or are part of a well-characterized metabolic pathway. Here, we used a multifaceted mass spectrometric (MS) approach to detect and identify the key metabolites that are present during BNF using the Medicago truncatula- Sinorhizobium meliloti association as the model system. High mass accuracy and high resolution matrix-assisted laser desorption/ionization (MALDI) and electrospray ionization (ESI) Orbitrap instruments were used in this study and provide complementary results for more in-depth characterization of the nitrogen-fixation process. We used well-characterized plant and bacterial mutants to highlight differences between the metabolites that are present in functional versus nonfunctional nodules. Our study highlights the benefits of using a combination of mass spectrometric techniques to detect differences in metabolite composition and the distributions of these metabolites in plant biology.

  7. Multifaceted Investigation of Metabolites During Nitrogen Fixation in Medicago via High Resolution MALDI-MS Imaging and ESI-MS

    PubMed Central

    Gemperline, Erin; Jayaraman, Dhileepkumar; Maeda, Junko; Ané, Jean-Michel; Li, Lingjun

    2014-01-01

    Legumes have developed the unique ability to establish a symbiotic relationship with soil bacteria known as rhizobia. This interaction results in the formation of root nodules in which rhizobia thrive and reduce atmospheric dinitrogen into plant-usable ammonium through biological nitrogen fixation (BNF). Due to the availability of genetic information for both of the symbiotic partners, the Medicago truncatula–Sinorhizobium meliloti association is an excellent model for examining the BNF process. Although metabolites are important in this symbiotic association, few studies have investigated the array of metabolites that influence this process. Of these studies, most target only a few specific metabolites, the roles of which are either well known or are part of a well-characterized metabolic pathway. Here, we used a multifaceted mass spectrometric (MS) approach to detect and identify the key metabolites that are present during BNF using the Medicago truncatula–Sinorhizobium meliloti association as the model system. High mass accuracy and high resolution matrix-assisted laser desorption/ionization (MALDI) and electrospray ionization (ESI) Orbitrap instruments were used in this study and provide complementary results for more in-depth characterization of the nitrogen-fixation process. We used well-characterized plant and bacterial mutants to highlight differences between the metabolites that are present in functional vs. non-functional nodules. Our study highlights the benefits of using a combination of mass spectrometric techniques to detect differences in metabolite composition and the distributions of these metabolites in plant biology. PMID:25323862

  8. Nitrogen fixation genetics and regulation in a Pseudomonas stutzeri strain associated with rice.

    PubMed

    Desnoues, Nicole; Lin, Min; Guo, Xianwu; Ma, Luyan; Carreño-Lopez, Ricardo; Elmerich, Claudine

    2003-08-01

    The Pseudomonas stutzeri strain A1501 (formerly known as Alcaligenes faecalis) fixes nitrogen under microaerobic conditions in the free-living state and colonizes rice endophytically. The authors characterized a region in strain A1501, corresponding to most of the nif genes and the rnf genes, involved in electron transport to nitrogenase in Rhodobacter capsulatus. The region contained three groups of genes arranged in the same order as in Azotobacter vinelandii: (1) nifB fdx ORF3 nifQ ORF5 ORF6; (2) nifLA-rnfABCDGEF-nifY2/nafY; (3) ORF13 ORF12-nifHDK-nifTY ORF1 ORF2-nifEN. Unlike in A. vinelandii, where these genes are not contiguous on the chromosome, but broken into two regions of the genome, the genes characterized here in P. stutzeri are contiguous and present on a 30 kb region in the genome of this organism. Insertion mutagenesis confirmed that most of the nif and the rnf genes in A1501 were essential for nitrogen fixation. Using lacZ fusions it was found that nif and rnf gene expression was under the control of ntrBC, nifLA and rpoN and that the rnf gene products were involved in the regulation of the nitrogen fixation process. PMID:12904565

  9. Persistence of biological nitrogen fixation in high latitude grass-clover grasslands under different management practices

    NASA Astrophysics Data System (ADS)

    Tzanakakis, Vasileios; Sturite, Ievina; Dörsch, Peter

    2016-04-01

    Biological nitrogen fixation (BNF) can substantially contribute to N supply in permanent grasslands, improving N yield and forage quality, while reducing inorganic N inputs. Among the factors critical to the performance of BNF in grass-legume mixtures are selected grass and legume species, proportion of legumes, the soil-climatic conditions, in particular winter conditions, and management practices (e.g. fertilization and compaction). In high latitude grasslands, low temperatures can reduce the performance of BNF by hampering the legumés growth and by suppressing N2 fixation. Estimation of BNF in field experiments is not straightforward. Different methods have been developed providing different results. In the present study, we evaluated the performance of BNF, in a newly established field experiment in North Norway over four years. The grassland consisted of white clover (Trifolium repens L.) and red clover (Trifolium pretense L.) sawn in three proportions (0, 15 and 30% in total) together with timothy (Pheum pretense L.) and meadow fescue (Festuca pratensis L.). Three levels of compaction were applied each year (no tractor, light tractor, heavy tractor) together with two different N rates (110 kg N/ha as cattle slurry or 170 kg N/ha as cattle slurry and inorganic N fertilizer). We applied two different methods, the 15N natural abundance and the difference method, to estimate BNF in the first harvest of each year. Overall, the difference method overestimated BNF relative to the 15N natural abundance method. BNF in the first harvest was compared to winter survival of red and white clover plants, which decreased with increasing age of the grassland. However, winter conditions did not seem to affect the grassland's ability to fix N in spring. The fraction of N derived from the atmosphere (NdfA) in white and red clover was close to 100% in each spring, indicating no suppression of BNF. BNF increased the total N yield of the grasslands by up to 75%, mainly due to high

  10. Discovery of symbiotic nitrogen fixation and chemoautotrophy in cold-water corals.

    PubMed

    Middelburg, Jack J; Mueller, Christina E; Veuger, Bart; Larsson, Ann I; Form, Armin; van Oevelen, Dick

    2015-01-01

    Cold-water corals (CWC) are widely distributed around the world forming extensive reefs at par with tropical coral reefs. They are hotspots of biodiversity and organic matter processing in the world's deep oceans. Living in the dark they lack photosynthetic symbionts and are therefore considered to depend entirely on the limited flux of organic resources from the surface ocean. While symbiotic relations in tropical corals are known to be key to their survival in oligotrophic conditions, the full metabolic capacity of CWC has yet to be revealed. Here we report isotope tracer evidence for efficient nitrogen recycling, including nitrogen assimilation, regeneration, nitrification and denitrification. Moreover, we also discovered chemoautotrophy and nitrogen fixation in CWC and transfer of fixed nitrogen and inorganic carbon into bulk coral tissue and tissue compounds (fatty acids and amino acids). This unrecognized yet versatile metabolic machinery of CWC conserves precious limiting resources and provides access to new nitrogen and organic carbon resources that may be essential for CWC to survive in the resource-depleted dark ocean. PMID:26644069

  11. Discovery of symbiotic nitrogen fixation and chemoautotrophy in cold-water corals

    PubMed Central

    Middelburg, Jack J.; Mueller, Christina E.; Veuger, Bart; Larsson, Ann I.; Form, Armin; Oevelen, Dick van

    2015-01-01

    Cold-water corals (CWC) are widely distributed around the world forming extensive reefs at par with tropical coral reefs. They are hotspots of biodiversity and organic matter processing in the world’s deep oceans. Living in the dark they lack photosynthetic symbionts and are therefore considered to depend entirely on the limited flux of organic resources from the surface ocean. While symbiotic relations in tropical corals are known to be key to their survival in oligotrophic conditions, the full metabolic capacity of CWC has yet to be revealed. Here we report isotope tracer evidence for efficient nitrogen recycling, including nitrogen assimilation, regeneration, nitrification and denitrification. Moreover, we also discovered chemoautotrophy and nitrogen fixation in CWC and transfer of fixed nitrogen and inorganic carbon into bulk coral tissue and tissue compounds (fatty acids and amino acids). This unrecognized yet versatile metabolic machinery of CWC conserves precious limiting resources and provides access to new nitrogen and organic carbon resources that may be essential for CWC to survive in the resource-depleted dark ocean. PMID:26644069

  12. Impact of the ahas transgene for herbicides resistance on biological nitrogen fixation and yield of soybean.

    PubMed

    Hungria, Mariangela; Nakatani, André Shigueyoshi; Souza, Rosinei Aparecida; Sei, Fernando Bonafé; de Oliveira Chueire, Ligia Maria; Arias, Carlos Arrabal

    2015-02-01

    Studies on the effects of transgenes in soybean [Glycine max (L.) Merr.] and the associated use of specific herbicides on biological nitrogen fixation (BNF) are still few, although it is important to ensure minimal impacts on benefits provided by the root-nodule symbiosis. Cultivance CV127 transgenic soybean is a cultivar containing the ahas gene, which confers resistance to herbicides of the imidazolinone group. The aim of this study was to assess the effects of the ahas transgene and of imidazolinone herbicide on BNF parameters and soybean yield. A large-scale set of field experiments was conducted, for three cropping seasons, at nine sites in Brazil, with a total of 20 trials. The experiment was designed as a completely randomized block with four replicates and the following treatments: (T1) near isogenic transgenic soybean (Cultivance CV127) + herbicide of the imidazolinone group (imazapyr); (T2) near isogenic transgenic soybean + conventional herbicides; and (T3) parental conventional soybean (Conquista) + conventional herbicides; in addition, two commercial cultivars were included, Monsoy 8001 (M-SOY 8001) (T4), and Coodetec 217 (CD 217) (T5). At the R2 growth stage, plants were collected and BNF parameters evaluated. In general, there were no effects on BNF parameters due to the transgenic trait or associated with the specific herbicide. Similarly, at the final harvest, no grain-yield effects were detected related to the ahas gene or to the specific herbicide. However, clear effects on BNF and grain yield were attributed to location and cropping season. PMID:25201300

  13. Efficient Inactivation of Symbiotic Nitrogen Fixation Related Genes in Lotus japonicus Using CRISPR-Cas9

    PubMed Central

    Wang, Longxiang; Wang, Longlong; Tan, Qian; Fan, Qiuling; Zhu, Hui; Hong, Zonglie; Zhang, Zhongming; Duanmu, Deqiang

    2016-01-01

    The targeted genome editing technique, CRISPR/Cas9 system, has been widely used to modify genes of interest in a predictable and precise manner. In this study, we describe the CRISPR/Cas9-mediated efficient editing of representative SNF (symbiotic nitrogen fixation) related genes in the model legume Lotus japonicus via Agrobacterium-mediated stable or hairy root transformation. We first predicted nine endogenous U6 genes in Lotus and then demonstrated the efficacy of the LjU6-1 gene promoter in driving expression of single guide RNAs (sgRNAs) by using a split yellow fluorescence protein (YFP) reporter system to restore the fluorescence in Arabidopsis protoplasts. Next, we chose a customized sgRNA targeting SYMRK (symbiosis receptor-like kinase) loci and achieved ~35% mutagenic efficiency in 20 T0 transgenic plants, two of them containing biallelic homozygous mutations with a 2-bp deletion near the PAM region. We further designed two sgRNAs targeting three homologous leghemoglobin loci (LjLb1, LjLb2, LjLb3) for testing the possibility of generating multi-gene knockouts. 20 out of 70 hairy root transgenic plants exhibited white nodules, with at least two LjLbs disrupted in each plant. Compared with the constitutively active CaMV 35S promoter, the nodule-specific LjLb2 promoter was also effective in gene editing in nodules by hairy root transformation. Triple mutant knockout of LjLbs was also obtained by stable transformation using two sgRNAs. Collectively, these studies demonstrate that the CRISPR/Cas9 system should greatly facilitate functional analyses of SNF related genes in Lotus japonicus.

  14. Nitrogen fixation and nitrogenase (nifH) expression in tropical waters of the eastern north atlantic.

    SciTech Connect

    Turk, K. A.; Rees, A. P.; Zehr, J. P.; Pereira, N.; Swift, P.; Shelley, R.; Lohan, M.; Woodward, E. M. S.; Gilbert, J.

    2011-01-01

    Expression of nifH in 28 surface water samples collected during fall 2007 from six stations in the vicinity of the Cape Verde Islands (north-east Atlantic) was examined using reverse transcription-polymerase chain reaction (RT-PCR)-based clone libraries and quantitative RT-PCR (RT-qPCR) analysis of seven diazotrophic phylotypes. Biological nitrogen fixation (BNF) rates and nutrient concentrations were determined for these stations, which were selected based on a range in surface chlorophyll concentrations to target a gradient of primary productivity. BNF rates greater than 6 nmolN I{sup -1} h{sup -1} were measured at two of the near-shore stations where high concentrations of Fe and PO{sub 4}{sup 3-} were also measured. Six hundred and five nifH transcripts were amplified by RT-PCR, of which 76% are described by six operational taxonomic units, including Trichodesmium and the uncultivated UCYN-A, and four non-cyanobacterial diazotrophs that clustered with uncultivated Proteobacteria. Although all five cyanobacterial phylotypes quantified in RT-qPCR assays were detected at different stations in this study, UCYN-A contributed most significantly to the pool of nifH transcripts in both coastal and oligotrophic waters. A comparison of results from RT-PCR clone libraries and RT-qPCR indicated that a {gamma}-proteobacterial phylotype was preferentially amplified in clone libraries, which underscores the need to use caution interpreting clone-library-based nifH studies, especially when considering the importance of uncultivated proteobacterial diazotrophs.

  15. Nitrogen fixation and nitrogenase (nifH) expression in tropical waters of the eastern North Atlantic

    PubMed Central

    A Turk, Kendra; Rees, Andrew P; Zehr, Jonathan P; Pereira, Nicole; Swift, Paul; Shelley, Rachel; Lohan, Maeve; Woodward, E Malcolm S; Gilbert, Jack

    2011-01-01

    Expression of nifH in 28 surface water samples collected during fall 2007 from six stations in the vicinity of the Cape Verde Islands (north-east Atlantic) was examined using reverse transcription-polymerase chain reaction (RT-PCR)-based clone libraries and quantitative RT-PCR (RT-qPCR) analysis of seven diazotrophic phylotypes. Biological nitrogen fixation (BNF) rates and nutrient concentrations were determined for these stations, which were selected based on a range in surface chlorophyll concentrations to target a gradient of primary productivity. BNF rates greater than 6 nmolN l−1 h−1 were measured at two of the near-shore stations where high concentrations of Fe and PO43− were also measured. Six hundred and five nifH transcripts were amplified by RT-PCR, of which 76% are described by six operational taxonomic units, including Trichodesmium and the uncultivated UCYN-A, and four non-cyanobacterial diazotrophs that clustered with uncultivated Proteobacteria. Although all five cyanobacterial phylotypes quantified in RT-qPCR assays were detected at different stations in this study, UCYN-A contributed most significantly to the pool of nifH transcripts in both coastal and oligotrophic waters. A comparison of results from RT-PCR clone libraries and RT-qPCR indicated that a γ-proteobacterial phylotype was preferentially amplified in clone libraries, which underscores the need to use caution interpreting clone-library-based nifH studies, especially when considering the importance of uncultivated proteobacterial diazotrophs. PMID:21228888

  16. Distribution and Evolution of Nitrogen Fixation Genes in the Phylum Bacteroidetes

    PubMed Central

    Inoue, Jun-ichi; Oshima, Kenshiro; Suda, Wataru; Sakamoto, Mitsuo; Iino, Takao; Noda, Satoko; Hongoh, Yuichi; Hattori, Masahira; Ohkuma, Moriya

    2015-01-01

    Diazotrophs had not previously been identified among bacterial species in the phylum Bacteroidetes until the rapid expansion of bacterial genome sequences, which revealed the presence of nitrogen fixation (nif) genes in this phylum. We herein determined the draft genome sequences of Bacteroides graminisolvens JCM 15093T and Geofilum rubicundum JCM 15548T. In addition to these and previously reported ‘Candidatus Azobacteroides pseudotrichonymphae’ and Paludibacter propionicigenes, an extensive survey of the genome sequences of diverse Bacteroidetes members revealed the presence of a set of nif genes (nifHDKENB) in strains of Dysgonomonas gadei, Dysgonomonas capnocytophagoides, Saccharicrinis fermentans, and Alkaliflexus imshenetskii. These eight species belonged to and were distributed sporadically within the order Bacteroidales. Acetylene reduction activity was detected in the five species examined, strongly suggesting their diazotrophic nature. Phylogenetic analyses showed monophyletic clustering of the six Nif protein sequences in the eight Bacteroidales species, implying that nitrogen fixation is ancestral to Bacteroidales and has been retained in these species, but lost in many other lineages. The identification of nif genes in Bacteroidales facilitates the prediction of the organismal origins of related sequences directly obtained from various environments. PMID:25736980

  17. Environmental and Genotypic Effects on the Respiration Associated with Symbiotic Nitrogen Fixation in Peas 1

    PubMed Central

    Mahon, John D.

    1979-01-01

    Estimated values for the respiration associated with symbiotic nitrogen fixation in Pisum sativum L. were independent of irradiance, temperature, plant age, and CO2 concentration, despite large variation in the total rates of C2H2 reduction and root + nodule respiration. Similar values were also found in Phaseolus vulgaris L., Vicia faba L. and Glycine max (L.) Merr. Among all combinations of four Pisum cultivars with four Rhizobium leguminosarum inoculants only the plant genotype significantly affected the fixation-linked respiration, although both plant and bacterial types significantly influenced the total rate of C2H2 reduction. On the basis of measured rates of H2 evolution and C2H2 reduction, or total nitrogen gain in the same system, the least respiration per unit of ammonia produced symbiotically was estimated as 4.8 to 6.9 moles CO2 (mole NH3)−1 in Laxton's Progress and the greatest as 9.3 to 13.3 moles CO2 (mole NH3)−1 in an Indian cultivar, as compared to a theoretical minimum respiration requirement of 4.7 moles CO2 (mole NH3)−1 in peas. PMID:16660833

  18. Effect of mineral phosphate solubilization on biological nitrogen fixation by diazotrophic cyanobacteria.

    PubMed

    Yandigeri, Mahesh S; Meena, Kamlesh Kumar; Srinivasan, R; Pabbi, Sunil

    2011-01-01

    The ability of two diazotrophic cyanobacteria Westiellopsis prolifica and Anabaena variabilis were examined to solubilize extracellular insoluble tricalcium phosphate (TCP) and Mussorie rock phosphate (MRP). The two strains exhibited a differential response to insoluble forms of phosphorus used. W. prolifica showed better growth in presence of MRP while A. variabilis proliferated better in presence of TCP. Biological nitrogen fixation measured in terms of acetylene reduction (AR) activity showed significant variation among the concentrations of TCP or MRP and time of incubation. W. prolifica and A. variabilis showed maximum AR activity on 14 and 21 days of incubation respectively. In general AR activity in presence of MRP was always less than that in presence of TCP at all concentrations. Among the two cyanobacteria A. variabilis was best in terms of P-solubilization and nitrogen fixation and TCP (20 mg P l(-1)) was the best source of insoluble P rather than MRP or K(2)HPO(4). PMID:22282628

  19. Iron deficiency increases growth and nitrogen-fixation rates of phosphorus-deficient marine cyanobacteria.

    PubMed

    Garcia, Nathan S; Fu, Feixue; Sedwick, Peter N; Hutchins, David A

    2015-01-01

    Marine dinitrogen (N2)-fixing cyanobacteria have large impacts on global biogeochemistry as they fix carbon dioxide (CO2) and fertilize oligotrophic ocean waters with new nitrogen. Iron (Fe) and phosphorus (P) are the two most important limiting nutrients for marine biological N2 fixation, and their availabilities vary between major ocean basins and regions. A long-standing question concerns the ability of two globally dominant N2-fixing cyanobacteria, unicellular Crocosphaera and filamentous Trichodesmium, to maintain relatively high N2-fixation rates in these regimes where both Fe and P are typically scarce. We show that under P-deficient conditions, cultures of these two cyanobacteria are able to grow and fix N2 faster when Fe deficient than when Fe replete. In addition, growth affinities relative to P increase while minimum concentrations of P that support growth decrease at low Fe concentrations. In Crocosphaera, this effect is accompanied by a reduction in cell sizes and elemental quotas. Relatively high growth rates of these two biogeochemically critical cyanobacteria in low-P, low-Fe environments such as those that characterize much of the oligotrophic ocean challenge the common assumption that low Fe levels can have only negative effects on marine primary producers. The closely interdependent influence of Fe and P on N2-fixing cyanobacteria suggests that even subtle shifts in their supply ratio in the past, present and future oceans could have large consequences for global carbon and nitrogen cycles. PMID:24972068

  20. Aerosol Deposition of Molybdenum: A Control on Nitrogen-Fixation and Tropical Forest Function

    NASA Astrophysics Data System (ADS)

    Wong, M.; Howarth, R. W.; Marino, R. M.; Mahowald, N. M.; Williams, E. R.

    2015-12-01

    Nitrogen fixation, the primary source of new nitrogen (N) to tropical forests, is exclusively catalyzed by the nitrogenase enzyme, which almost always requires molybdenum (Mo). Increasing evidence in recent years suggests that Mo availability may be low in highly weathered soils and can constrain N-fixation rates. Mo is generally either present in a highly soluble form (MoO42-) that is susceptible to leaching or tightly bound in minerals unavailable for biological uptake. To address how Mo is retained in highly weathered tropical systems to support N-fixation, atmospheric transport through dust and sea-salt aerosol spray were examined. Using a global atmospheric transport model computed from modeled meteorological fields, extrapolated dust and sea-salt aerosol Mo sources were used to calculate global distribution of Mo deposition. Dust deposition occurs across the entirety of some tropical forests, particularly the world's largest tropical forest in the Amazon Basin. The model indicates that the Amazon Basin receives substantial inputs of dust, especially the entire northern Amazon Basin, while the southern half receives less. Most of the dust reaching the Amazon originates from the Sahara Desert, and about half of this dust originates from one part of the Sahara, the Bodélé Depression. Mo in dust from the Bodélé Depression was measured with an average concentration of 1.14 ± 0.05 μg/g, similar to the crustal abundance. The model predicts Mo inputs from sea-salt aerosols in coastal regions up to 0.002 mg m-2yr-1. Significant sea-salt deposition occurs up to 300 km inland. Mo from fossil fuel combustion and biomass burning were also evaluated to determine the potential influence of anthropogenic emissions on releasing Mo into the environment.

  1. Nitrite fixation by humic substances: Nitrogen-15 nuclear magnetic resonance evidence for potential intermediates in chemodenitrification

    USGS Publications Warehouse

    Thorn, K.A.; Mikita, M.A.

    2000-01-01

    Studies have suggested that NO2/-, produced during nitrification and denitrification, can become incorporated into soil organic matter and, in one of the processes associated with chemodenitrification, react with organic matter to form trace N gases, including N2O. To gain an understanding of the nitrosation chemistry on a molecular level, soil and aquatic humic substances were reacted with 15N-labeled NaNO2, and analyzed by liquid phase 15N and 13C nuclear magnetic resonance (NMR). The International Humic Substances Society (IHSS) Pahokee peat and peat humic acid were also reacted with Na15NO2 and analyzed by solid-state 15N NMR. In Suwannee River, Armadale, and Laurentian fulvic acids, phenolic rings and activated methylene groups underwent nitrosation to form nitrosophenols (quinone monoximes) and ketoximes, respectively. The oximes underwent Beckmann rearrangements to 2??amides, and Beckmann fragmentations to nitriles. The nitriles in turn underwent hydrolysis to 1??amides. Peaks tentatively identified as imine, indophenol, or azoxybenzene nitrogens were clearly present in spectra of samples nitrosated at pH 6 but diminished at pH 3. The 15N NMR spectrum of the peat humic acid exhibited peaks corresponding with N-nitroso groups in addition to nitrosophenols, ketoximes, and secondary Beckmann reaction products. Formation of N-nitroso groups was more significant in the whole peat compared with the peat humic acid. Carbon-13 NMR analyses also indicated the occurrence of nitrosative demethoxylation in peat and soil humic acids. Reaction of 15N-NH3 fixated fulvic acid with unlabeled NO2/- resulted in nitrosative deamination of aminohydroquinone N, suggesting a previously unrecognized pathway for production of N2 gas in soils fertilized with NH3.Studies have suggested that NO2-, produced during nitrification and denitrification, can become incorporated into soil organic matter and, in one of the processes associated with chemodenitrification, react with organic

  2. Data-based assessment of environmental controls on global marine nitrogen fixation

    NASA Astrophysics Data System (ADS)

    Luo, Y.-W.; Lima, I. D.; Karl, D. M.; Deutsch, C. A.; Doney, S. C.

    2014-02-01

    There are a number of hypotheses concerning the environmental controls on marine nitrogen fixation (NF). Most of these hypotheses have not been assessed against direct measurements on the global scale. In this study, we use ~ 500 depth-integrated field measurements of NF covering the Pacific and Atlantic oceans to test whether the spatial variance of these measurements can be explained by the commonly hypothesized environmental controls, including measurement-based surface solar radiation, mixed layer depth, average solar radiation in the mixed layer, sea surface temperature, wind speed, surface nitrate and phosphate concentrations, surface excess phosphate (P*) concentration and subsurface minimum dissolved oxygen (in upper 500 m), as well as model-based P* convergence and atmospheric dust deposition. By conducting simple linear regression and stepwise multiple linear regression (MLR) analyses, surface solar radiation (or sea surface temperature) and subsurface minimum dissolved oxygen are identified as the predictors that explain the most spatial variance in the observed NF data, although it is unclear why the observed NF decreases when the level of subsurface minimum dissolved oxygen is higher than ~ 150 μM. Dust deposition and wind speed do not appear to influence the spatial patterns of NF on global scale. The weak correlation between the observed NF and the P* convergence and concentrations suggests that the available data currently remain insufficient to fully support the hypothesis that spatial variability in denitrification is the principal control on spatial variability in marine NF. By applying the MLR-derived equation, we estimate the global-integrated NF at 74 (error range 51-110) Tg N yr-1 in the open ocean, acknowledging that it could be substantially higher as the 15N2-assimilation method used by most of the field samples underestimates NF. More field NF samples in the Pacific and Indian oceans, particularly in the oxygen minimum zones

  3. Physical forcing of nitrogen fixation and diazotroph community structure in the North Pacific subtropical gyre

    NASA Astrophysics Data System (ADS)

    Church, Matthew J.; Mahaffey, Claire; Letelier, Ricardo M.; Lukas, Roger; Zehr, Jonathan P.; Karl, David M.

    2009-06-01

    Dinitrogen (N2) fixing microorganisms (termed diazotrophs) exert important control on the ocean carbon cycle. However, despite increased awareness on the roles of these microorganisms in ocean biogeochemistry and ecology, the processes controlling variability in diazotroph distributions, abundances, and activities remain largely unknown. In this study, we examine 3 years (2004-2007) of approximately monthly measurements of upper ocean diazotroph community structure and rates of N2 fixation at Station ALOHA (22°45'N, 158°W), the field site for the Hawaii Ocean Time-series program in the central North Pacific subtropical gyre (NPSG). The structure of the N2-fixing microorganism assemblage varied widely in time with unicellular N2-fixing microorganisms frequently dominating diazotroph abundances in the late winter and early spring, while filamentous microorganisms (specifically various heterocyst-forming cyanobacteria and Trichodesmium spp.) fluctuated episodically during the summer. On average, a large fraction (˜80%) of the daily N2 fixation was partitioned into the biomass of <10 μm microorganisms. Rates of N2 fixation were variable in time, with peak N2 fixation frequently coinciding with periods when heterocystous N2-fixing cyanobacteria were abundant. During the summer months when sea surface temperatures exceeded 25.2°C and concentrations of nitrate plus nitrite were at their annual minimum, rates of N2 fixation often increased during periods of positive sea surface height anomalies, as reflected in satellite altimetry. Our results suggest mesoscale physical forcing may comprise an important control on variability in N2 fixation and diazotroph community structure in the NPSG.

  4. Genetic Variability in Nodulation and Root Growth Affects Nitrogen Fixation and Accumulation in Pea

    PubMed Central

    Bourion, Virginie; Laguerre, Gisele; Depret, Geraldine; Voisin, Anne-Sophie; Salon, Christophe; Duc, Gerard

    2007-01-01

    Background and Aims Legume nitrogen is derived from two different sources, symbiotically fixed atmospheric N2 and soil N. The effect of genetic variability of root and nodule establishment on N acquisition and seed protein yield was investigated under field conditions in pea (Pisum sativum). In addition, these parameters were related to the variability in preference for rhizobial genotypes. Methods Five different spring pea lines (two hypernodulating mutants and three cultivars), previously identified in artificial conditions as contrasted for both root and nodule development, were characterized under field conditions. Root and nodule establishment was examined from the four-leaf stage up to the beginning of seed filling and was related to the patterns of shoot dry matter and nitrogen accumulation. The genetic structure of rhizobial populations associated with the pea lines was obtained by analysis of nodule samples. The fraction of nitrogen derived from symbiotic fixation was estimated at the beginning of seed filling and at physiological maturity, when seed protein content and yield were determined. Key Results The hypernodulating mutants established nodules earlier and maintained them longer than was the case for the three cultivars, whereas their root development and nitrogen accumulation were lower. The seed protein yield was higher in ‘Athos’ and ‘Austin’, the two cultivars with increased root development, consistent with their higher N absorption during seed filling. Conclusion The hypernodulating mutants did not accumulate more nitrogen, probably due to the C cost for nodulation being higher than for root development. Enhancing exogenous nitrogen supply at the end of the growth cycle, by increasing the potential for root N uptake from soil, seems a good option for improving pea seed filling. PMID:17670753

  5. Symbiotic nitrogen fixation in the alpine community of a lichen heath of the Northwestern Caucasus Region (the Teberda Reserve)

    NASA Astrophysics Data System (ADS)

    Makarov, M. I.; Malysheva, T. I.; Ermak, A. A.; Onipchenko, V. G.; Stepanov, A. L.; Menyailo, O. V.

    2011-12-01

    The symbiotic fixation of atmospheric nitrogen by leguminous plants in the alpine community of a lichen heath at the Teberda State Biosphere Reserve is well adapted to low soil temperature characteristic for the altitude of 2800 m a.s.l. For the determination of the N fixation by isotopic methods (the method of the natural 15N abundance and the method of isotopic 15N dilution), Trifolium polyphyllum was taken as the control plant. This plant was used as it does not form symbiosis with the nitrogen-fixing bacteria in the highlands of the Northern Caucasus Region. The contribution of the N fixation to the N nutrition of different leguminous plant species as determined by the natural 15N abundance method amounted to 28-73% at δ15N0 = 0‰ and 46-117% at δ15N0 = -1‰; for the determination of the N fixation by the method of the isotopic label's dilution, it was 34-97%. The best correlation of the results obtained by these two isotopic methods was observed for the natural fractionation of the N isotopes in the course of the N fixation in the range of -0.5 to -0.7‰. The determination of the nitrogenase activity of the roots by the acetylene method confirmed the absence of N fixation in T. polyphyllum and its different contribution to the N nutrition of different species of leguminous plants.

  6. The influence of woody encroachment on the nitrogen cycle: fixation, storage and gas loss

    NASA Astrophysics Data System (ADS)

    Soper, F.; Sparks, J. P.

    2015-12-01

    Woody encroachment is a pervasive land cover change throughout the tropics and subtropics. Encroachment is frequently catalyzed by nitrogen (N)-fixing trees and the resulting N inputs potentially alter whole-ecosystem N cycling, accumulation and loss. In the southern US, widespread encroachment by legume Prosopis glandulosa is associated with increased soil total N storage, inorganic N concentrations, and net mineralization and nitrification rates. To better understand the effects of this process on ecosystem N cycling, we investigated patterns of symbiotic N fixation, N accrual and soil N trace gas and N2 emissions during Prosopis encroachment into the southern Rio Grande Plains. Analyses of d15N in foliage, xylem sap and plant-available soil N suggested that N fixation rates increase with tree age and are influenced by abiotic conditions. A model of soil N accrual around individual trees, accounting for atmospheric inputs and gas losses, generates lifetimes N fixation estimates of up to 9 kg for a 100-year-old tree and current rates of 7 kg N ha-1 yr-1. However, these N inputs and increased soil cycling rates do not translate into increased N gas losses. Two years of field measurements of a complete suite of N trace gases (ammonia, nitrous oxide, nitric oxide and other oxidized N compounds) found no difference in flux between upland Prosopis groves and adjacent unencroached grasslands. Total emissions for both land cover types average 0.56-0.65 kg N ha-1 yr-1, comparable to other southern US grasslands. Additional lab experiments suggested that N2 losses are low and that field oxygen conditions are not usually conducive to denitrification. Taken together, results suggest that this ecosystem is currently experiencing a period of net N accrual under ongoing encroachment.

  7. Stable Isotope Evidence of Variation in Nitrogen Fixation by Cyanobacteria in Coastal Ecosystems

    NASA Astrophysics Data System (ADS)

    Paul, V.; Clementz, M.

    2006-12-01

    Increased nutrient loading via both natural and anthropogenic factors has been reported as one possible mechanism for the recent increase in the occurrence and intensity of harmful algal blooms (HAB) in coastal ecosystems. Influx of iron, phosphorous, and organic carbon have proven to be significant stimulating factors for HAB, since the benthic cyanobacteria that often make up these blooms are capable of nitrogen-fixation and require these nutrients for this process as well as photosynthesis. These cyanobacteria can switch to direct uptake of dissolved inorganic nitrogen (DIN), however, when concentrations are high enough to energetically favor this source, suggesting that high nitrogen input may also stimulate HAB. Given the distinct isotope differences between atmospheric N2 (0‰) and anthropogenic sources of DIN (>6‰), measurement of the δ15N composition of cyanobacteria can provide a means of gauging the relative significance of anthropogenic versus atmospheric nitrogen to the growth of these blooms. Likewise, the δ13C composition of these primary producers is controlled by the δ13C composition of the DIC, and can be a second tracer of anthropogenic influx into marine ecosystems. A combined approach using both isotope tracers was employed to determine the significance of anthropogenic nitrogen on HAB in subtropical/tropical coastal marine ecosystems. Samples of cyanobacteria and associated macroalgae were collected from three coastal sites in Guam (Facpi Point, Tanguisson, and Ypao Beach), one locality in Hawaii, and three sites in southern Florida (Pepper Park, Fort Lauderdale, Florida Keys). Following removal of marine carbonates via an acid rinse, the δ13C and δ15N values were determined for each species. Cyanobacterial δ15N values ranged from -2.3‰ to 7.7‰ with the highest values reported from sites in Guam. Only cyanobacteria sampled from Hawaii showed no isotope evidence of an anthropogenic source for nitrogen. A strong negative correlation

  8. Biological nitrogen fixation: rates, patterns and ecological controls in terrestrial ecosystems

    USGS Publications Warehouse

    Vitousek, Peter M.; Menge, Duncan N.L.; Reed, Sasha C.; Cleveland, Cory C.

    2013-01-01

    New techniques have identified a wide range of organisms with the capacity to carry out biological nitrogen fixation (BNF)—greatly expanding our appreciation of the diversity and ubiquity of N fixers—but our understanding of the rates and controls of BNF at ecosystem and global scales has not advanced at the same pace. Nevertheless, determining rates and controls of BNF is crucial to placing anthropogenic changes to the N cycle in context, and to understanding, predicting and managing many aspects of global environmental change. Here, we estimate terrestrial BNF for a pre-industrial world by combining information on N fluxes with 15N relative abundance data for terrestrial ecosystems. Our estimate is that pre-industrial N fixation was 58 (range of 40–100) Tg N fixed yr−1; adding conservative assumptions for geological N reduces our best estimate to 44 Tg N yr−1. This approach yields substantially lower estimates than most recent calculations; it suggests that the magnitude of human alternation of the N cycle is substantially larger than has been assumed.

  9. Biological nitrogen fixation: rates, patterns and ecological controls in terrestrial ecosystems

    PubMed Central

    Vitousek, Peter M.; Menge, Duncan N. L.; Reed, Sasha C.; Cleveland, Cory C.

    2013-01-01

    New techniques have identified a wide range of organisms with the capacity to carry out biological nitrogen fixation (BNF)—greatly expanding our appreciation of the diversity and ubiquity of N fixers—but our understanding of the rates and controls of BNF at ecosystem and global scales has not advanced at the same pace. Nevertheless, determining rates and controls of BNF is crucial to placing anthropogenic changes to the N cycle in context, and to understanding, predicting and managing many aspects of global environmental change. Here, we estimate terrestrial BNF for a pre-industrial world by combining information on N fluxes with 15N relative abundance data for terrestrial ecosystems. Our estimate is that pre-industrial N fixation was 58 (range of 40–100) Tg N fixed yr−1; adding conservative assumptions for geological N reduces our best estimate to 44 Tg N yr−1. This approach yields substantially lower estimates than most recent calculations; it suggests that the magnitude of human alternation of the N cycle is substantially larger than has been assumed. PMID:23713117

  10. Membrane energization in relation with nitrogen fixation in Azotobacter vinelandii and Rhizobium leguminosarum bacteroids.

    PubMed

    Veeger, C; Laane, C; Scherings, G; van Zeeland Wolbers, L

    1978-01-01

    Nitrogen fixation in A. vinelandii and R. leguminosarum bacteroides shows identical characteristics with respect to the dependence on membrane energization, the sensitivity to uncouplers, the ATP/ADP-ratio, and the dependences on flavodoxinhydroquinone as electrondonor. Although we have been successful in preparing inside-out vesicles which can be energized, attempts to couple these membranes to N2-ase were still unsuccessful. One of the major problems could be the failure to energize these vesicles directly by ATP. Although subject to polymerisation after addition of MgCl2, it could be shown that the actual mol.wt. of the O2-stable N2-ase complex is about 300,000 in agreement with a 1:1:1 stoichiometry of the three constituent proteins, namely, component I, component II and the 2Fe-2S protein. PMID:667180

  11. Effects of acidic rain and ozone on nitrogen fixation and photosynthesis in the lichen lobaria pulmonaria (L. ) Hoffm

    SciTech Connect

    Sigal, L.L.; Johnston, J.W.

    1986-01-01

    The lichen Lobaria pulmonaria was subjected to ozone fumigations at 118, 235 and 353 mcg/cu m and simulated acidic rain at pH levels of 2.6, 4.2 and 5.6 for 5 days (M,W,F,M,W) during a 10-day period. Acidic rain at pH 2.6 caused significant reduction in nitrogen fixation and gross photosynthesis of 100 and 90%, respectively, and thallus bleaching was apparent. There were no significant differences between the pH 5.6 and 4.2 treatments in either gross photosynthesis or nitrogen fixation, and the color of the lichen thalli was unchanged. The effect of ozone on nitrogen fixation and photosynthesis over the range of concentrations used was not significant, but there was a trend toward reduced nitrogen fixation with increasing O/sub 3/ concentration. There were no significant ozone-acidic rain interactions. The threshold for response to rain acidity for L. pulmonaria lies between pH 2.6 and 4.2, and the acidity of wet deposition in parts of the United States may fall in the range.

  12. Comparison of two Cellulomonas strains and their interaction with Azospirillum brasilense in degradation of wheat straw and associated nitrogen fixation

    SciTech Connect

    Halsall, D.M.; Gibson, A.H.

    1986-04-01

    A mutant strain of Cellulomonas sp. CS1-17 was compared with Cellulomonas gelida 2480 as the cellulolytic component of a mixed culture which was responsible for the breakdown of wheat straw to support asymbiotic nitrogen fixation by Azospirillum brasilense Sp7 (ATCC 29145). Cellulomonas sp. strain CS1-17 was more efficient than was C. gelida in cellulose breakdown at lower oxygen concentrations and, in mixed culture with A. brasilense, it supported higher nitrogenase activity(C/sub 2/H/sub 2/ reduction) and nitrogen fixation with straw as the carbon source. Based on gravimetric determinations of straw breakdown and total N determinations, the efficiency of nitrogen fixation was 72 and 63 mg of N per g of straw utilized for the mixtures containing Cellulomonas sp. and C. gelida, respectively. Both Cellulomonas spp. and Azospirillum spp. exhibited a wide range of pH tolerance. When introduced into sterilized soil, the Cellulomonas sp.-Azospirillum brasilense association was more effective in nitrogen fixation at a pH of 7.0 than at the native soil pH (5.6). This was also true of the indigenous diazotrophic microflora of this soil. The potential implications of this work to the field situation are discussed. 16 references.

  13. Global changes in the transcript and metabolic profiles during symbiotic nitrogen fixation in phosphorus-stressed common bean plants

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Phosphorus (P) deficiency is widespread in regions where the common bean (Phaseolus vulgaris L.), the most important legume for human consumption, is produced and is perhaps the factor that most limits nitrogen (N) fixation. Global gene expression and metabolome approaches were used to investigate t...

  14. Identification of a cis-acting element in nitrogen fixation genes recognized by CnfR in the nonheterocystous nitrogen-fixing cyanobacterium Leptolyngbya boryana.

    PubMed

    Tsujimoto, Ryoma; Kamiya, Narumi; Fujita, Yuichi

    2016-08-01

    The filamentous cyanobacterium Leptolyngbya boryana has the ability to fix nitrogen without any heterocysts under microoxic conditions. Previously, we identified the cnfR gene for a master transcriptional activator for nitrogen fixation (nif) genes in a 50-kb gene cluster containing nif and nif-related genes in L. boryana. We showed that CnfR activates the transcription of nif genes in response to low oxygen conditions, which allows the oxygen-vulnerable enzyme nitrogenase to function. However, the regulatory mechanism that underlies regulation by CnfR remains unknown. In this study, we identified a conserved cis-acting element that is recognized by CnfR. We established a reporter system in the non-diazotrophic cyanobacterium Synechocystis sp. PCC 6803 using luciferase genes (luxAB). Reporter analysis was performed with a series of truncated and modified upstream regulatory regions of nifB and nifP. The cis-element can be divided into nine motifs I-IX, and it is located 76 bp upstream of the transcriptional start sites of nifB and nifP. Six motifs of them are essential for transcriptional activation by CnfR. This cis-acting element is conserved in the upstream regions of nif genes in all diazotrophic cyanobacteria, including Anabaena and Cyanothece, thereby suggesting that the transcriptional regulation by CnfR is widespread in nitrogen-fixing cyanobacteria. PMID:27119437

  15. Microgravity Effects on the Early Events of Biological Nitrogen Fixation in Medicago Truncatula: Results from the SyNRGE Experiment

    NASA Astrophysics Data System (ADS)

    Stutte, Gary W.; Roberts, Michael S.

    2013-02-01

    SyNRGE (Symbiotic Nodulation in a Reduced Gravity Environment) was a sortie mission on STS-135 in the Biological Research in Canisters (BRIC) hardware to study the effect of μg on a plant-microbe symbiosis resulting in biological nitrogen fixation. Medicago truncatula, a model species for the legume family, was inoculated with its bacterial symbiont, Sinorhizobium meliloti, to observe early biomolecular events associated with infection and nodulation in Petri Dish Fixation Units (PDFU’s). Two sets of experiments were conducted in orbit and in 24-hour delayed ground controls. Experiments were designed to determine if S. meliloti would infect M. truncatula and initiate biomolecular changes associated with nodule formation and if the μg environment altered the host plant and/or bacteria to induce nodule formation upon return to 1g. Initial analysis results demonstrate that the legumes and bacteria cultivated in μg have potential to develop a symbiotic interaction, but suggest that μg alters their ability to form nodules upon return to 1g. (Research supported by NASA ESMD/ Advance Capabilities Division grant NNX10AR09A)

  16. An alternate photosynthetic electron donor system for PSI supports light dependent nitrogen fixation in a non-heterocystous cyanobacterium, Plectonema boryanum.

    PubMed

    Misra, Hari S; Khairnar, Nivedita P; Mahajan, Suresh K

    2003-01-01

    Plectonema boryanum exhibits temporal separation of photosynthesis and nitrogen fixation under diazotrophic conditions. During nitrogen fixation, the photosynthetic electron transport chain becomes impaired, which leads to the uncoupling of the PSII and PSI activities. A 30-40% increase in PSI activity and continuous generation of ATP through light-dependent processes seem to support the nitrogen fixation. The use of an artificial electron carrier that shuttles electrons between the plastoquinone pool and plastocyanin, bypassing cytochrome b/f complex, enhanced the photosynthetic electron transport activity five to six fold during nitrogen fixation. Measuring of full photosynthetic electron transport activity using methyl voilogen as a terminal acceptor revealed that the photosynthetic electron transport components beyond plastocyanin might be functional. Further, glycolate can act as a source of electrons for PSI for the nitrogen fixing cells, which have residual PSII activity. Under conditions when PSI becomes largely independent of PSII and glycolate provides electrons for PSI activity, the light-dependent nitrogen fixation also was stimulated by glycolate. These results suggest that during nitrogen fixation, when the photosynthetic electron transport from PSII is inhibited at the level of cytochrome b/f complex, an alternate electron donor system for PSI may be required for the cells to carry out light dependent nitrogen fixation. PMID:12685043

  17. Nitrogen fixation in different biogeochemical niches along a 120 000-year chronosequence in New Zealand.

    PubMed

    Menge, Duncan N L; Hedin, Lars O

    2009-08-01

    Biological nitrogen fixation (BNF) is the major nitrogen (N) input in many terrestrial ecosystems, yet we know little about the mechanisms and feedbacks that control this process in natural ecosystems. We here examine BNF in four taxonomically and ecologically different groups over the course of forest ecosystem development. At nine sites along the Franz Josef soil chronosequence (South Westland, New Zealand) that range in age from 7 to 120000 yr old, we quantified BNF from the symbiotic plant Coriaria arborea, cyanolichens (primarily Pseudocyphellaria spp.), bryophytes (many species), and heterotrophic bacteria in leaf litter. We specifically examined whether these groups could act as "nitrostats" at the ecosystem level, turning BNF on when N is scarce (early in primary succession) and off when N is plentiful (later in succession and retrogression). Coriaria was abundant and actively fixing (approximately 11 kg N x ha(-1) x yr(-1)) in the youngest and most N-poor site (7 yr old), consistent with nitrostat dynamics. Coriaria maintained high BNF rates independent of soil N availability, however, until it was excluded from the community after a single generation. We infer that Coriaria is an obligate N fixer and that the nitrostat feedback is mechanistically governed by species replacement at the community level, rather than down-regulation of BNF at the physiological scale. Biological nitrogen fixation inputs from lichens (means of 0-2 kg N x ha(-1) x yr(-1)), bryophytes (0.7-10 kg N x ha(-1) x yr(-1)), and litter (1-2 kg N x ha(-1) x yr(-1)) were driven primarily by changes in density, which peaked at intermediate-aged sites (and increased with soil N availability) for both lichens and bryophytes, and grew monotonically with soil age (but did not change with soil N) for litter. This non-nitrostatic link between soil N availability and lichen/bryophyte BNF likely stems from increased tree biomass in more fertile sites, which increases epiphytic moisture conditions

  18. Oxygen-Poor Microzones as Potential Sites of Microbial N2 Fixation in Nitrogen-Depleted Aerobic Marine Waters

    PubMed Central

    Paerl, Hans W.; Prufert, Leslie E.

    1987-01-01

    The nitrogen-deficient coastal waters of North Carolina contain suspended bacteria potentially able to fix N2. Bioassays aimed at identifying environmental factors controlling the development and proliferation of N2 fixation showed that dissolved organic carbon (as simple sugars and sugar alcohols) and particulate organic carbon (derived from Spartina alterniflora) additions elicited and enhanced N2 fixation (nitrogenase activity) in these waters. Nitrogenase activity occurred in samples containing flocculent, mucilage-covered bacterial aggregates. Cyanobacterium-bacterium aggregates also revealed N2 fixation. In all cases bacterial N2 fixation occurred in association with surficial microenvironments or microzones. Since nitrogenase is oxygen labile, we hypothesized that the aggregates themselves protected their constituent microbes from O2. Microelectrode O2 profiles revealed that aggregates had lower internal O2 tensions than surrounding waters. Tetrazolium salt (2,3,5-triphenyl-3-tetrazolium chloride) reduction revealed that patchy zones existed both within microbes and extracellularly in the mucilage surrounding microbes where free O2 was excluded. Triphenyltetrazolium chloride reduction also strongly inhibited nitrogenase activity. These findings suggest that N2 fixation is mediated by the availability of the appropriate types of reduced microzones. Organic carbon enrichment appears to serve as an energy and structural source for aggregate formation, both of which were required for eliciting N2 fixation responses of these waters. Images PMID:16347337

  19. Relationship between biomass production and nitrogen fixation under drought stress conditions in peanut genoytpes with different levels of drought resistance

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The relationship between biomass production and N2 fixation under drought stress conditions in peanut genotypes with different levels of drought resistance is not well understood. The objective of this study was to determine the effect of drought on biomass production and N2 fixation by evaluating t...

  20. Spatial and Temporal Variation in Feather Moss Associated Nitrogen Fixation in Coniferous and Deciduous Dominated Alaskan Boreal Forests

    NASA Astrophysics Data System (ADS)

    Jean, M.; Mack, M. C.; Johnstone, J. F.

    2015-12-01

    Dominant canopy tree species have strong effects on the composition and function of understory species. In boreal forests, forest floor bryophytes and their associated microbes are a primary source of ecosystem nitrogen (N) inputs, and thus an important process regulating ecosystem productivity. Bryophyte composition and abundance varies with forest composition, yet how such changes can affect ecosystem processes such as N fixation is still poorly understood. Our goal is to investigate how cyanobacteria-based N fixation occurring in the two most common feather mosses in the Alaskan boreal forest (Pleurozium schreberi and Hylocomium splendens) varies among coniferous and deciduous forest types, over the growing season, and across a nutrient availability gradient. Twelve patches of H. splendens and P. schreberi were identified in three pairs (blocks) of adjacent stands of paper birch (Betula neoalaskana) and black spruce (Picea mariana) near Fairbanks, interior Alaska. Sampling occurred in one block in June, July, August, and September 2014, and in the three blocks once in August 2014. Moss leaf area, moisture and weight, as well as environmental variables such as air temperature and canopy cover were recorded. Fixation rates were consistently higher for P. schreberi than for H. splendens. Overall, N fixation rates were lower in birch than in spruce stands and peaked in August, or July for P. schreberi in birch stands. Moreover, fixation rates varied along the nutrient availability gradient, with fixation rates higher where nutrient availability was lower. This difference was especially clear in spruce stands. Our preliminary results suggest that moss species, canopy type, and environmental factors all influence N fixation rates in Alaskan boreal forests. Our results will enhance the knowledge of the processes that drive N fixation in boreal forests, which is important for predicting ecosystem consequences of changing forest composition.

  1. Isotopic evidence for biological nitrogen fixation by molybdenum-nitrogenase from 3.2 Gyr.

    PubMed

    Stüeken, Eva E; Buick, Roger; Guy, Bradley M; Koehler, Matthew C

    2015-04-30

    Nitrogen is an essential nutrient for all organisms that must have been available since the origin of life. Abiotic processes including hydrothermal reduction, photochemical reactions, or lightning discharge could have converted atmospheric N2 into assimilable NH4(+), HCN, or NOx species, collectively termed fixed nitrogen. But these sources may have been small on the early Earth, severely limiting the size of the primordial biosphere. The evolution of the nitrogen-fixing enzyme nitrogenase, which reduces atmospheric N2 to organic NH4(+), thus represented a major breakthrough in the radiation of life, but its timing is uncertain. Here we present nitrogen isotope ratios with a mean of 0.0 ± 1.2‰ from marine and fluvial sedimentary rocks of prehnite-pumpellyite to greenschist metamorphic grade between 3.2 and 2.75 billion years ago. These data cannot readily be explained by abiotic processes and therefore suggest biological nitrogen fixation, most probably using molybdenum-based nitrogenase as opposed to other variants that impart significant negative fractionations. Our data place a minimum age constraint of 3.2 billion years on the origin of biological nitrogen fixation and suggest that molybdenum was bioavailable in the mid-Archaean ocean long before the Great Oxidation Event. PMID:25686600

  2. Physiological and isotopic characteristics of nitrogen fixation by hyperthermophilic methanogens: Key insights into nitrogen anabolism of the microbial communities in Archean hydrothermal systems

    NASA Astrophysics Data System (ADS)

    Nishizawa, Manabu; Miyazaki, Junichi; Makabe, Akiko; Koba, Keisuke; Takai, Ken

    2014-08-01

    Hyperthermophilic hydrogenotrophic methanogens are considered to be one of the most predominant primary producers in hydrogen (H2)-abundant hydrothermal environments in the present-day ocean and throughout the history of the Earth. However, the nitrogen sources supporting the development of microbial communities in hydrothermal environments remain poorly understood. We have investigated, for the first time, methanogenic archaea commonly found in deep-sea hydrothermal environments to understand their physiological properties (growth kinetics, energetics, and metal requirements) and isotopic characteristics during the fixation of dinitrogen (N2), which is an abundant but less-bioavailable compound in hydrothermal fluids. Culture experiments showed that Methanocaldococcus strain (Mc 1-85N) (Topt = 85 °C) and Methanothermococcus strain (Mt 5-55N) (Topt = 55 °C) assimilated N2 and ammonium, but not nitrate. Previous phylogenetic studies have predicted that the Methanocaldococcus and Methanothermococcus lineages have nitrogenases, key enzymes for N2 fixation, with biochemically uncharacterised active site metal cofactors. We showed that Mt 5-55N required molybdenum for the nitrogenase to function, implying a molybdenum-bearing cofactor in the strain. Molybdenum also stimulated diazotrophic (i.e., N2-fixing) growth of Mc 1-85N, though further experiments are required to test whether the strain contains a molybdenum-dependent nitrogenase. Importantly, Mc 1-85N exhibited an apparently lower requirement of and higher tolerance to molybdenum and iron than Mt 5-55N. Furthermore, both strains produced more 15N-depleted biomass (-4‰ relative to N2) than that previously reported for diazotrophic photosynthetic prokaryotes. These results demonstrate that diazotrophic hyperthermophilic methanogens can be broadly distributed in seafloor and subseafloor hydrothermal environments, where the availability of transition metals is variable and where organic carbon, organic nitrogen

  3. Interaction of root nodule size and oxygen pressure on the rate of nitrogen fixation by cowpea and peanut

    SciTech Connect

    Sen, D.; Weaver, R.W.

    1987-04-01

    Size and anatomical features of nodules influence the rate of O/sub 2/ diffusion into nodules. Availability of oxygen can be a limiting factor in nitrogen fixation. Larger nodules have thicker cortices and low surface to volume ratio leading to lower rates of gaseous diffusion. Increased oxygen pressure in the environment alters the rate of nitrogen fixation but the rate of change may depend on the nodule size. This was investigated by measuring /sup 15/N/sub 2/ incorporation into nodules. Root nodules from 38 day old cowpea and peanut plants were collected and sorted into size groups having diameters of >3 mm, 2-3 mm, and just below 2 mm. Samples of each size group were enclosed in tubes and exposed to various combination of oxygen (8-28%) and /sup 15/N/sub 2/. With higher O/sub 2/ pressure all nodules showed increased N/sub 2/ fixation but the largest nodules showed the maximum increase. Specific activity of larger nodules was higher for N/sub 2/ fixation. For the sizes of nodules examined the largest nodules did not reflect any of the disadvantages of the large size but the benefits of higher rates of O/sub 2/ entry was evident.

  4. Growth condition study of algae function in ecosystem for CO2 bio-fixation.

    PubMed

    Tsai, David Dah-Wei; Ramaraj, Rameshprabu; Chen, Paris Honglay

    2012-02-01

    Algae niche play a crucial role on carbon cycle and have great potential for CO(2) sequestration. This study was to investigate the CO(2) bio-fixation by the high rate pond (HRP) to mimic the algae function of nature. All the reactors can keep CO(2) consumption efficiencies over 100%. The statistical analyses proved HRPs were close to the natural system from all the growth conditions. The HRP could show the "natural optimization as nature" to perform as well as the artificial reactor of continuously stirred tank reactor (CSTR). In the nutrition study, the carbon mass balance indicated CO(2) was the main carbon source. Accordingly, the HRPs can keep a neutral pH range to provide dissolved oxygen (DO), to promote total nitrogen (TN)/total phosphorous (TP) removal efficiencies and to demonstrate self-purification process. Furthermore, the observations of different nitrogen species in the reactors demonstrated that the major nitrogen source was decided by pH. This finding logically explained the complex nitrogen uptake by algae in nature. Consequently, this study took advantage of HRP to explore the processes of efficient CO(2) uptake with the corresponding growth condition in the ecosystem. Those results contributed the further understanding of the role of CO(2) bio-fixation in nature and demonstrated HRP could be a potential ecological engineering alternative. PMID:22196805

  5. The reallocation of carbon in P deficient lupins affects biological nitrogen fixation.

    PubMed

    Kleinert, Aleysia; Venter, Mauritz; Kossmann, Jens; Valentine, Alexander

    2014-11-01

    It is not known how phosphate (P) deficiency affects the allocation of carbon (C) to biological nitrogen fixation (BNF) in legumes. The alteration of the respiratory and photosynthetic C costs of BNF was investigated under P deficiency. Although BNF can impose considerable sink stimulation on host respiratory and photosynthetic C, it is not known how the change in the C and energy allocation during P deficiency may affect BNF. Nodulated Lupinus luteus plants were grown in sand culture, using a modified Long Ashton nutrient solution containing no nitrogen (N) for ca. four weeks, after which one set was exposed to a P-deficient nutrient medium, while the other set continued growing on a P-sufficient nutrient medium. Phosphorus stress was measured at 20 days after onset of P-starvation. During P stress the decline in nodular P levels was associated with lower BNF and nodule growth. There was also a shift in the balance of photosynthetic and respiratory C toward a loss of C during P stress. Below-ground respiration declined under limiting P conditions. However, during this decline there was also a shift in the proportion of respiratory energy from maintenance toward growth respiration. Under P stress, there was an increased allocation of C toward root growth, thereby decreasing the amount of C available for maintenance respiration. It is therefore possible that the decline in BNF under P deficiency may be due to this change in resource allocation away from respiration associated with direct nutrient uptake, but rather toward a long term nutrient acquisition strategy of increased root growth. PMID:25155758

  6. Nitrogen fixation in peanut nodules during dark periods and detopped conditions with special reference to lipid bodies

    SciTech Connect

    Siddique, A.M.; Bal, A.K. )

    1991-03-01

    The peanut plant (Arachis hypogaea L.), unlike other known legumes, can sustain nitrogen fixation when prolonged periods of darkness or detopping curtail the supply of photosynthate to the nodule. This ability to withstand photosynthate stress is attributed to the presence of lipid bodies in infected nodule cells. In both dark-treated and detopped plants, the lipid bodies show a gradual decrease in numbers, suggesting their utilization as a source of energy and carbon for nitrogen fixation. Lipolytic activity can be localized in the lipid bodies, and the existence of {beta}-oxidation pathway and glyoxylate cycle is shown by the release of {sup 14}CO{sub 2} from {sup 14}C lineoleoyl coenzyme A by the nodule homogenate.

  7. Carbon and nitrogen fixation differ between successional stages of biological soil crusts in the Colorado Plateau and Chihuahuan Desert

    USGS Publications Warehouse

    Housman, D.C.; Powers, H.H.; Collins, A.D.; Belnap, J.

    2006-01-01

    Biological soil crusts (cyanobacteria, mosses and lichens collectively) perform essential ecosystem services, including carbon (C) and nitrogen (N) fixation. Climate and land-use change are converting later successional soil crusts to early successional soil crusts with lower C and N fixation rates. To quantify the effect of such conversions on C and N dynamics in desert ecosystems we seasonally measured diurnal fixation rates in different biological soil crusts. We classified plots on the Colorado Plateau (Canyonlands) and Chihuahuan Desert (Jornada) as early (Microcoleus) or later successional (Nostoc/Scytonema or Placidium/Collema) and measured photosynthesis (Pn), nitrogenase activity (NA), and chlorophyll fluorescence (Fv/Fm) on metabolically active (moist) soil crusts. Later successional crusts typically had greater Pn, averaging 1.2-1.3-fold higher daily C fixation in Canyonlands and 2.4-2.8-fold higher in the Jornada. Later successional crusts also had greater NA, averaging 1.3-7.5-fold higher daily N fixation in Canyonlands and 1.3-25.0-fold higher in the Jornada. Mean daily Fv/Fm was also greater in later successional Canyonlands crusts during winter, and Jornada crusts during all seasons except summer. Together these findings indicate conversion of soil crusts back to early successional stages results in large reductions of C and N inputs into these ecosystems.

  8. Non-biological fixation of atmospheric nitrogen to nitrate on titanium dioxide and desert soil surfaces

    NASA Astrophysics Data System (ADS)

    Al-Taani, Ahmed A.

    Elevated nitrate levels have frequently been observed in soils and the associated groundwater in arid regions of the U.S, many of which are distant from anthropogenic sources. Although these elevated nitrate concentrations have generally been linked to atmospheric precipitation, the current study indicates that at least a portion of these nitrates may have been formed through photochemical and thermal transformation reactions on soil surfaces. Photochemical nitrogen fixation to nitrate was observed on pure TiO 2 (both anatase and rutile) and desert soil surfaces when exposed to sunlight from 2 to 80 days. The yields of nitrate were generally proportional to irradiation time and increased substantially when sodium hydroxide was added. Larger surface films of soils or TiO2 generated higher yields of nitrate. Soils with higher content of both titanium and calcium exhibit higher photoactivities, and the production rate varied slightly with particle size. Traces of nitrite and ammonia detected on irradiated TiO2 surface were similar to background levels, and are probably not intermediates in the formation of nitrate. TiO2 and soils obtained from Atacama Desert in northern Chile and Pyramid Lake, NV were irradiated with sunlight for 32 days in either 15N labeled or unlabeled nitrogen and produced nitrates enriched in 15N and that nearly all isotopic values were higher than that of atmospheric 15N. Nitrate produced photochemically on Atacama Desert soils have isotopic values that are similar to those of the subsoil nitrates of the Atacama Desert. During our experimental investigation and while preparing thin films of TiO2 by thermal evaporation of an aqueous suspension in Petri dishes, we consistently observed an increase in nitrate concentrations in all samples (even the controls) whenever TiO2 slurries came in contact with heat and air. An expanded series of experiments was carried out in a conventional oven in the absence of light; photocatalytic reactions are not

  9. A purple acid phosphatase plays a role in nodule formation and nitrogen fixation in Astragalus sinicus.

    PubMed

    Wang, Jianyun; Si, Zaiyong; Li, Fang; Xiong, Xiaobo; Lei, Lei; Xie, Fuli; Chen, Dasong; Li, Yixing; Li, Youguo

    2015-08-01

    The AsPPD1 gene from Astragalus sinicus encodes a purple acid phosphatase. To address the functions of AsPPD1 in legume-rhizobium symbiosis, its expression patterns, enzyme activity, subcellular localization, and phenotypes associated with its over-expression and RNA interference (RNAi) were investigated. The expression of AsPPD1 was up-regulated in roots and nodules after inoculation with rhizobia. Phosphate starvation reduced the levels of AsPPD1 transcripts in roots while increased those levels in nodules. We confirmed the acid phosphatase and phosphodiesterase activities of recombinant AsPPD1 purified from Pichia pastoris, and demonstrated its ability to hydrolyze ADP and ATP in vitro. Subcellular localization showed that AsPPD1 located on the plasma membranes in hairy roots and on the symbiosomes membranes in root nodules. Over-expression of AsPPD1 in hairy roots inhibited nodulation, while its silencing resulted in nodules early senescence and significantly decreased nitrogenase activity. Furthermore, HPLC measurement showed that AsPPD1 overexpression affects the ADP levels in the infected roots and nodules, AsPPD1 silencing affects the ratio of ATP/ADP and the energy charge in nodules, and quantitative observation demonstrated the changes of AsPPD1 transcripts level affected nodule primordia formation. Taken together, it is speculated that AsPPD1 contributes to symbiotic ADP levels and energy charge control, and this is required for effective nodule organogenesis and nitrogen fixation. PMID:26105827

  10. Short-term nitrate (nitrite) inhibition of nitrogen fixation in Azotobacter chroococcum

    SciTech Connect

    Cejudo, F.J.; Paneque, A.

    1986-01-01

    Nitrate-grown Azotobacter chroococcum ATCC 4412 cells lack the ability to fix N/sub 2/. Nitrogenase activity developed after the cells were suspended in a combined nitrogen-free medium and was paralleled by a concomitant decrease in nitrate assimilation capacity. In such treated cells exhibiting transitory nitrate assimilation and N/sub 2/-fixation capacity, nitrate or nitrite caused a short-term inhibitory effect on nitrogenase activity which ceased once the anion was exhausted from the medium. The glutamate analog L-methionine-DL-sulfoximine, an inhibitor of glutamine synthetase, prevented inhibition of nitrogenase activity by nitrate or nitrite without affecting the uptake of these anions, which were reduced and stoichiometrically released into the external medium as ammonium. Inhibition of nitrogenase by nitrate (nitrite) did not take place in A. chroococcum MCD1, which is unable to assimilate either. The authors conclude that the short-term inhibitory effect of nitrate (nitrite) on nitrogenase activity is due to some organic product(s) formed during the assimilation of the ammonium resulting from nitrate (nitrite) reduction.

  11. Isolation and Characterization of Frankia sp. Strain FaC1 Genes Involved in Nitrogen Fixation.

    PubMed

    Ligon, J M; Nakas, J P

    1987-10-01

    Genomic DNA was isolated from Frankia sp. strain FaC1, an Alnus root nodule endophyte, and used to construct a genomic library in the cosmid vector pHC79. The genomic library was screened by in situ colony hybridization to identify clones of Frankia nitrogenase (nif) genes based on DNA sequence homology to structural nitrogenase genes from Klebsiella pneumoniae. Several Frankia nif clones were isolated, and hybridization with individual structural nitrogenase gene fragments (nifH, nifD, and nifK) from K. pneumoniae revealed that they all contain the nifD and nifK genes, but lack the nifH gene. Restriction endonuclease mapping of the nifD and nifK hybridizing region from one clone revealed that the nifD and nifK genes in Frankia sp. are contiguous, while the nifH gene is absent from a large region of DNA on either side of the nifDK gene cluster. Additional hybridizations with gene fragments derived from K. pneumoniae as probes and containing other genes involved in nitrogen fixation demonstrated that the Frankia nifE and nifN genes, which play a role in the biosynthesis of the iron-molybdenum cofactor, are located adjacent to the nifDK gene cluster. PMID:16347453

  12. Associative nitrogen fixation, C4 photosynthesis, and the evolution of spittlebugs (Hemiptera: Cercopidae) as major pests of neotropical sugarcane and forage grasses.

    PubMed

    Thompson, V

    2004-06-01

    Neotropical grass-feeding spittlebugs of several genera are important pests of pasture grasses from the southeastern USA to northern Argentina, and of sugarcane from southern Mexico to southern Brazil, causing estimated reductions of up to 70% in yield and estimated monetary losses of 840-2100 million US dollars annually. With few exceptions, the species badly damaged by these spittlebugs are introduced C4 grasses that exhibit associative nitrogen fixation. This study synthesizes evidence that the pest status of many tropical and subtropical grass-feeding spittlebugs is linked to associative N-fixation in their C4 hosts. Recognition that associative N-fixation is a major factor in spittlebug host preferences should deepen understanding of spittlebug agricultural ecology and facilitate efforts to combat spittlebug pests. In particular, spittlebugs should be susceptible to manipulation of xylem transport solutes. However, reduction of nitrate fertilizer rates, increase in ammonium fertilizer rates, or enhancement of associative N-fixation as a consequence of genetic engineering could make hosts more susceptible to spittlebug attack. Because of their predilection for C4 grasses, spittlebugs present a clear counterexample to the hypothesis that herbivores prefer C3 plants to C4 plants. Finally, it appears that declines in atmospheric carbon dioxide levels during recent geological history promoted the proliferation of C4 grasses. This, compounded by human agricultural activities, has driven an ecological and evolutionary radiation of grass-feeding spittlebugs that presents continuing opportunities for the evolution of spittlebug pests. PMID:15191620

  13. EFFECTS OF ACIDIC RAIN AND OZONE ON NITROGEN FIXATION AND PHOTOSYNTHESIS IN THE LICHEN 'LOBARIA PULMONARIA' (L.) HOFFM

    EPA Science Inventory

    The lichen Lobaria pulmonaria was subjected to ozone fumigations at 118, 235 and 353 mcg/cu m and simulated acidic rain at pH levels of 2.6, 4.2 and 5.6 for 5 days (M,W,F,M,W) during a 10-day period. Acidic rain at pH 2.6 caused significant reduction in nitrogen fixation and gros...

  14. Ureide assay for measuring nitrogen fixation by nodulated soybean calibrated by sup 15 N methods. [Glycine max

    SciTech Connect

    Herridge, D.F. ); Peoples, M.B. )

    1990-06-01

    We report experiments to quantify the relationships between the relative abundance of ureide-N in root-bleeding sap, vacuum-extracted sap, and hot water extracts of stems and petioles of nodulated soybean (Glycine max (L.) Merrill cv Bragg) and the proportion of plant N derived from nitrogen fixation. Additional experiments examined the effects of plant genotype and strain of rhizobia on these relationships. In each of the five experiments reported, plants of cv Bragg (experiment 1), cv Lincoln (experiments 3, 4, 5), or six cultivars/genotypes (experiment 2) were grown in a sand:vermiculite mixture in large pots in a naturally lit, temperature-controlled glasshouse during summer. Pots were inoculated at sowing with effective Bradyrhizobium japonicum CB 1809 (USDA 136) or with one of 21 different strains of rhizobia. The proportions of plant N derived from nitrogen fixation were determined using {sup 15}N dilution. Results show that assessment of nitrogen fixation by soybean using the ureide technique should now be possible with the standard curves presented, irrespective of genotype or strain of rhizobia occupying the nodules.

  15. Growth-promoting Sphingomonas paucimobilis ZJSH1 associated with Dendrobium officinale through phytohormone production and nitrogen fixation

    PubMed Central

    Yang, Suijuan; Zhang, Xinghai; Cao, Zhaoyun; Zhao, Kaipeng; Wang, Sai; Chen, Mingxue; Hu, Xiufang

    2014-01-01

    Growth-promoting Sphingomonas paucimobilis ZJSH1, associated with Dendrobium officinale, a traditional Chinese medicinal plant, was characterized. At 90 days post-inoculation, strain ZJSH1 significantly promoted the growth of D. officinale seedlings, with increases of stems by 8.6% and fresh weight by 7.5%. Interestingly, the polysaccharide content extracted from the inoculated seedlings was 0.6% higher than that of the control. Similar growth promotion was observed with the transplants inoculated with strain ZJSH1. The mechanism of growth promotion was attributed to a combination of phytohormones and nitrogen fixation. Strain ZJSH1 was found using the Kjeldahl method to have a nitrogen fixation activity of 1.15 mg l−1, which was confirmed by sequencing of the nifH gene. Using high-performance liquid chromatography-mass spectrometry, strain ZJSH1 was found to produce various phytohormones, including salicylic acid (SA), indole-3-acetic acid (IAA), Zeatin and abscisic acid (ABA). The growth curve showed that strain ZJSH1 grew well in the seedlings, especially in the roots. Accordingly, much higher contents of SA, ABA, IAA and c-ZR were detected in the inoculated seedlings, which may play roles as both phytohormones and ‘Systemic Acquired Resistance’ drivers. Nitrogen fixation and secretion of plant growth regulators (SA, IAA, Zeatin and ABA) endow S. paucimobilis ZJSH1 with growth-promoting properties, which provides a potential for application in the commercial growth of D. officinale. PMID:25142808

  16. Comparative organization of nitrogen fixation-specific genes from Azotobacter vinelandii and Klebsiella pneumoniae: DNA sequence of the nifUSV genes.

    PubMed Central

    Beynon, J; Ally, A; Cannon, M; Cannon, F; Jacobson, M; Cash, V; Dean, D

    1987-01-01

    In the facultative anaerobe Klebsiella pneumoniae 17 nitrogen fixation-specific genes (nif genes) have been identified. Homologs to 12 of these genes have now been isolated from the aerobic diazotroph Azotobacter vinelandii. Comparative studies have indicated that these diverse microorganisms share striking similarities in the genetic organization of their nif genes and in the primary structure of their individual nif gene products. In this study the complete nucleotide sequence of the nifUSV gene clusters from both K. pneumoniae and A. vinelandii were determined. These genes are identically organized on their respective genomes, and the individual genes and their products exhibit a high degree of interspecies sequence homology. PMID:3040672

  17. Proteome Profiling of the Rhodobacter capsulatus Molybdenum Response Reveals a Role of IscN in Nitrogen Fixation by Fe-Nitrogenase

    PubMed Central

    Hoffmann, Marie-Christine; Wagner, Eva; Langklotz, Sina; Pfänder, Yvonne; Hött, Sina; Bandow, Julia E.

    2015-01-01

    ABSTRACT Rhodobacter capsulatus is capable of synthesizing two nitrogenases, a molybdenum-dependent nitrogenase and an alternative Mo-free iron-only nitrogenase, enabling this diazotroph to grow with molecular dinitrogen (N2) as the sole nitrogen source. Here, the Mo responses of the wild type and of a mutant lacking ModABC, the high-affinity molybdate transporter, were examined by proteome profiling, Western analysis, epitope tagging, and lacZ reporter fusions. Many Mo-controlled proteins identified in this study have documented or presumed roles in nitrogen fixation, demonstrating the relevance of Mo control in this highly ATP-demanding process. The levels of Mo-nitrogenase, NifHDK, and the Mo storage protein, Mop, increased with increasing Mo concentrations. In contrast, Fe-nitrogenase, AnfHDGK, and ModABC, the Mo transporter, were expressed only under Mo-limiting conditions. IscN was identified as a novel Mo-repressed protein. Mo control of Mop, AnfHDGK, and ModABC corresponded to transcriptional regulation of their genes by the Mo-responsive regulators MopA and MopB. Mo control of NifHDK and IscN appeared to be more complex, involving different posttranscriptional mechanisms. In line with the simultaneous control of IscN and Fe-nitrogenase by Mo, IscN was found to be important for Fe-nitrogenase-dependent diazotrophic growth. The possible role of IscN as an A-type carrier providing Fe-nitrogenase with Fe-S clusters is discussed. IMPORTANCE Biological nitrogen fixation is a central process in the global nitrogen cycle by which the abundant but chemically inert dinitrogen (N2) is reduced to ammonia (NH3), a bioavailable form of nitrogen. Nitrogen reduction is catalyzed by nitrogenases found in diazotrophic bacteria and archaea but not in eukaryotes. All diazotrophs synthesize molybdenum-dependent nitrogenases. In addition, some diazotrophs, including Rhodobacter capsulatus, possess catalytically less efficient alternative Mo-free nitrogenases, whose expression

  18. High levels of heterogeneity in diazotroph diversity and activity within a putative hotspot for marine nitrogen fixation.

    PubMed

    Messer, Lauren F; Mahaffey, Claire; M Robinson, Charlotte; Jeffries, Thomas C; Baker, Kirralee G; Bibiloni Isaksson, Jaime; Ostrowski, Martin; Doblin, Martina A; Brown, Mark V; Seymour, Justin R

    2016-06-01

    Australia's tropical waters represent predicted 'hotspots' for nitrogen (N2) fixation based on empirical and modelled data. However, the identity, activity and ecology of diazotrophs within this region are virtually unknown. By coupling DNA and cDNA sequencing of nitrogenase genes (nifH) with size-fractionated N2 fixation rate measurements, we elucidated diazotroph dynamics across the shelf region of the Arafura and Timor Seas (ATS) and oceanic Coral Sea during Austral spring and winter. During spring, Trichodesmium dominated ATS assemblages, comprising 60% of nifH DNA sequences, while Candidatus Atelocyanobacterium thalassa (UCYN-A) comprised 42% in the Coral Sea. In contrast, during winter the relative abundance of heterotrophic unicellular diazotrophs (δ-proteobacteria and γ-24774A11) increased in both regions, concomitant with a marked decline in UCYN-A sequences, whereby this clade effectively disappeared in the Coral Sea. Conservative estimates of N2 fixation rates ranged from <1 to 91 nmol l(-1) day(-1), and size fractionation indicated that unicellular organisms dominated N2 fixation during both spring and winter, but average unicellular rates were up to 10-fold higher in winter than in spring. Relative abundances of UCYN-A1 and γ-24774A11 nifH transcripts negatively correlated to silicate and phosphate, suggesting an affinity for oligotrophy. Our results indicate that Australia's tropical waters are indeed hotspots for N2 fixation and that regional physicochemical characteristics drive differential contributions of cyanobacterial and heterotrophic phylotypes to N2 fixation. PMID:26613341

  19. The interactive effects of temperature and light on biological nitrogen fixation in boreal forests

    Technology Transfer Automated Retrieval System (TEKTRAN)

    • Plant productivity is predicted to increase in northern latitudes due to climate warming; however, this may depend on whether biological N-fixation also increases. We evaluated how variation in temperature and light affect N-fixation by two boreal feather mosses, Pleurozium schreberi and Hylocomi...

  20. Origin and Evolution of Nitrogen Fixation Genes on Symbiosis Islands and Plasmid in Bradyrhizobium

    PubMed Central

    Okubo, Takashi; Piromyou, Pongdet; Tittabutr, Panlada; Teaumroong, Neung; Minamisawa, Kiwamu

    2016-01-01

    The nitrogen fixation (nif) genes of nodule-forming Bradyrhizobium strains are generally located on symbiosis islands or symbiosis plasmids, suggesting that these genes have been transferred laterally. The nif genes of rhizobial and non-rhizobial Bradyrhizobium strains were compared in order to infer the evolutionary histories of nif genes. Based on all codon positions, the phylogenetic tree of concatenated nifD and nifK sequences showed that nifDK on symbiosis islands formed a different clade from nifDK on non-symbiotic loci (located outside of symbiosis islands and plasmids) with elongated branches; however, these genes were located in close proximity, when only the 1st and 2nd codon positions were analyzed. The guanine (G) and cytosine (C) content of the 3rd codon position of nifDK on symbiosis islands was lower than that on non-symbiotic loci. These results suggest that nif genes on symbiosis islands were derived from the non-symbiotic loci of Bradyrhizobium or closely related strains and have evolved toward a lower GC content with a higher substitution rate than the ancestral state. Meanwhile, nifDK on symbiosis plasmids clustered with nifDK on non-symbiotic loci in the tree representing all codon positions, and the GC content of symbiotic and non-symbiotic loci were similar. These results suggest that nif genes on symbiosis plasmids were derived from the non-symbiotic loci of Bradyrhizobium and have evolved with a similar evolutionary pattern and rate as the ancestral state. PMID:27431195

  1. Organization and regulation of the genes for nitrogen fixation in Rhodopseudomonas capsulata

    SciTech Connect

    Haselkorn, R.

    1989-05-01

    The research carried out over the past two years with DOE support has led to the elucidation of the complete nucleotide sequence of three genes required for the transcription of the genes for nitrogen fixation in Rhodobacter capsulatus. These genes are called nifR1, nifR2 and nifR4 in R. capsulatus. They were found to be homologous to ntrC, ntrB and ntrA in Klebsiella, respectively. Genetic analysis of ammonia-constitutive (NiF{sup c}) mutants of R. capsulatus, isolated using a nifH::lac fusion, showed that ammonia repression involves components of the adenylylation cascade (e.g., the glnB gene) as in Klebsiella. Oxygen control of nif gene expression was linked to the degree of DNA supercoiling by showing that inhibitors of DNA gyrase prevent nif gene expression. Attempts to relate the degree of supercoiling or of gyrase activity in R. capsulatus to the oxygen level have been inconclusive. The gene encoding the DNA gyrase B subunit of R. capsulatus was cloned. The genes encoding the two large subunits of R. Capsulatus RNA polymerase were cloned, mapped and partially sequenced. The nif genes and the glnA gene are being physically mapped on the R. capsulatus chromosome using pulsed field electrophoresis to separate large segments of the bacterial chromosome. A start was made on the purification of R. capsulatus RNA polymerase. A system for expressing genes in R. capsulatus was applied to nifR4; analogous constructions will be made for nifR1, nifR2 and nifA.

  2. Dinitrogen fixation and dissolved organic nitrogen fueled primary production and particulate export during the VAHINE mesocosms experiment (New Caledonia lagoon)

    NASA Astrophysics Data System (ADS)

    Berthelot, H.; Moutin, T.; L'Helguen, S.; Leblanc, K.; Hélias, S.; Grosso, O.; Leblond, N.; Charrière, B.; Bonnet, S.

    2015-03-01

    In the oligotrophic ocean characterized by nitrate (NO3-) depletion in surface waters, dinitrogen (N2) fixation and dissolved organic nitrogen (DON) can represent significant nitrogen (N) sources for the ecosystem. Here we deployed in New Caledonia large in situ mesocosms in order to investigate (1) the contribution of N2 fixation and DON use to primary production (PP) and particle export and (2) the fate of the freshly produced particulate organic N (PON) i.e. whether it is preferentially accumulated and recycled in the water column or exported out of the system. The mesocosms were fertilized with phosphate (P) in order to prevent P-limitation and promote N2 fixation. The diazotrophic community was dominated by diatoms-diazotrophs associations (DDAs) during the first part of the experiment for 10 days (P1) followed by the unicellular N2-fixing cyanobacteria UCYN-C the 9 last days (P2) of the experiment. N2 fixation rates averaged 9.8 ± 4.0 and 27.7 ± 8.6 nM d-1 during P1 and P2, respectively. NO3- concentrations (< 40 nM) in the mesocosms were a negligible source of N indicating that N2 fixation was the main driver of new production all along the experiment. The contribution of v fixation to PP was not significantly different (p > 0.05) during P1 (9.0 ± 3.3%) and P2 (12.6 ± 6.1%). However, the e ratio that quantifies the efficiency of a system to export particulate organic carbon (POCexport) compared to PP (e ratio = POCexport/PP) was significantly higher (p < 0.05) during P2 (39.7 ± 24.9%) than during P1 (23.9 ± 20.2%) indicating that the production sustained by UCYN-C was more efficient at promoting C export than the production sustained by DDAs. During P1, PON was stable and the total amount of N provided by N2 fixation (0.10 ± 0.02 μM) was not significantly different (p > 0.05) from the total amount of PON exported (0.10 ± 0.04 μM), suggesting a rapid and probably direct export of the recently fixed N2 by the DDAs. During P2, both PON concentrations

  3. Effect of Protein Additives on Acetylene Reduction (Nitrogen Fixation) by Rhizobium in the Presence and Absence of Soybean Cells 1

    PubMed Central

    Anderson, Stephen J.; Phillips, Donald A.

    1976-01-01

    The effect of protein additives on acetylene reduction (N2 fixation) by Rhizobium associated with soybean cells (Glycine max [L.] Merr.) in vitro was studied. Acetylene reduction was promoted on the basal medium supplemented with 1.4 mg of N/ml supplied as aqueous extracts of hexane-extracted soybean, red kidney beans (Phaseolus vulgaris L.), or peas (Pisum sativum L.). Commercial samples of α-casein, or bovine serum albumin also promoted acetylene reduction at a concentration of 1.4 mg of N/ml of basal medium, but egg albumin supplying an equal amount of nitrogen to the basal medium completely suppressed acetylene reduction. Autoclaving the aqueous extract of hexane-extracted soybean meal had no effect on its ability to promote acetylene reduction. The presence of 40 mm succinate decreased acetylene reduction with leguminous proteins supplying 1.4 mg of N/ml but promoted acetylene reduction by Rhizobium 32H1-soybean cell associations on media containing α-casein, bovine serum albumin, or egg albumin suppling 1.4 mg of N/ml. Similar results were obtained with both cowpea Rhizobium 32H1 and Rhizobium japonicum 61A96. Pure cultures of Rhizobium 32H1 developed acetylene-reducing activity in the presence of soybean extract on basal agar medium and in vermiculite supplied with N-free mineral salts plus crude soybean meal. The results suggest that in certain situations, free living Rhizobium may reduce N2 under field conditions. PMID:16659592

  4. A JAZ Protein in Astragalus sinicus Interacts with a Leghemoglobin through the TIFY Domain and Is Involved in Nodule Development and Nitrogen Fixation

    PubMed Central

    Li, Yixing; Xu, Meng; Wang, Ning; Li, Youguo

    2015-01-01

    Leghemoglobins (Lbs) play an important role in legumes-rhizobia symbiosis. Lbs bind O2 and protect nitrogenase activity from damage by O2 in nodules, therefore, they are regarded as a marker of active nitrogen fixation in nodules. Additionally, Lbs are involved in the nitric oxide (NO) signaling pathway, acting as a NO scavenger during nodule development and nitrogen fixation. However, regulators responsible for Lb expression and modulation of Lb activity have not been characterized. In our previous work, a Jasmonate-Zim-domain (JAZ) protein interacting with a Lb (AsB2510) in Astragalus sinicus was identified and designated AsJAZ1. In this study, the interaction between AsJAZ1 and AsB2510 was verified using a yeast two-hybrid system and in vitro Glutathione S-transferase (GST) pull-down assays, resulting in identification of the interaction domain as a TIFY (previously known as zinc-finger protein expressed in inflorescence meristem, ZIM) domain. TIFY domain is named after the most conserved amino acids within the domain. Bimolecular fluorescence complementation (BiFC) was used to confirm the interaction between AsJAZ1 and AsB2510 in tobacco cells, demonstrating that AsJAZ1-AsB2510 interaction was localized to the cell membrane and cytoplasm. Furthermore, the expression patterns and the symbiotic phenotypes of AsJAZ1 were investigated. Knockdown of AsJAZ1 expression via RNA interference led to decreased number of nodules, abnormal development of bacteroids, accumulation of poly-x-hydroxybutyrate (PHB) and loss of nitrogenase activity. Taken together, our results suggest that AsJAZ1 interacts with AsB2510 and participates in nodule development and nitrogen fixation. Our results provide novel insights into the functions of Lbs or JAZ proteins during legume-rhizobia symbiosis. PMID:26460857

  5. A JAZ Protein in Astragalus sinicus Interacts with a Leghemoglobin through the TIFY Domain and Is Involved in Nodule Development and Nitrogen Fixation.

    PubMed

    Li, Yixing; Xu, Meng; Wang, Ning; Li, Youguo

    2015-01-01

    Leghemoglobins (Lbs) play an important role in legumes-rhizobia symbiosis. Lbs bind O2 and protect nitrogenase activity from damage by O2 in nodules, therefore, they are regarded as a marker of active nitrogen fixation in nodules. Additionally, Lbs are involved in the nitric oxide (NO) signaling pathway, acting as a NO scavenger during nodule development and nitrogen fixation. However, regulators responsible for Lb expression and modulation of Lb activity have not been characterized. In our previous work, a Jasmonate-Zim-domain (JAZ) protein interacting with a Lb (AsB2510) in Astragalus sinicus was identified and designated AsJAZ1. In this study, the interaction between AsJAZ1 and AsB2510 was verified using a yeast two-hybrid system and in vitro Glutathione S-transferase (GST) pull-down assays, resulting in identification of the interaction domain as a TIFY (previously known as zinc-finger protein expressed in inflorescence meristem, ZIM) domain. TIFY domain is named after the most conserved amino acids within the domain. Bimolecular fluorescence complementation (BiFC) was used to confirm the interaction between AsJAZ1 and AsB2510 in tobacco cells, demonstrating that AsJAZ1-AsB2510 interaction was localized to the cell membrane and cytoplasm. Furthermore, the expression patterns and the symbiotic phenotypes of AsJAZ1 were investigated. Knockdown of AsJAZ1 expression via RNA interference led to decreased number of nodules, abnormal development of bacteroids, accumulation of poly-x-hydroxybutyrate (PHB) and loss of nitrogenase activity. Taken together, our results suggest that AsJAZ1 interacts with AsB2510 and participates in nodule development and nitrogen fixation. Our results provide novel insights into the functions of Lbs or JAZ proteins during legume-rhizobia symbiosis. PMID:26460857

  6. Transcriptional Profiling of Nitrogen Fixation and the Role of NifA in the Diazotrophic Endophyte Azoarcus sp. Strain BH72

    PubMed Central

    Sarkar, Abhijit; Reinhold-Hurek, Barbara

    2014-01-01

    Background The model endophyte Azoarcus sp. strain BH72 is known to contribute fixed nitrogen to its host Kallar grass and also expresses nitrogenase genes endophytically in rice seedlings. Availability of nitrogen is a signal regulating the transcription of nitrogenase genes. Therefore, we analysed global transcription in response to differences in the nitrogen source. Methodology/Principal Findings A DNA microarray, comprising 70-mer oligonucleotides representing 3989 open reading frames of the genome of strain BH72, was used for transcriptome studies. Transcription profiles of cells grown microaerobically on N2 versus ammonium were compared. Expression of 7.2% of the genes was significantly up-regulated, and 5.8% down-regulated upon N2 fixation, respectively. A parallel genome-wide prediction of σ54-type promoter elements mapped to the upstream region of 38 sequences of which 36 were modulated under the N2 response. In addition to modulation of genes related to N2 fixation, the expressions of gene clusters that might be related to plant-microbe interaction and of several transcription factors were significantly enhanced. While comparing under N2-fixation conditions the transcriptome of wild type with a nifLA− insertion mutant, NifA being the essential transcriptional activator for nif genes, 24.5% of the genome was found to be affected in expression. A genome-wide prediction of 29 NifA binding sequences matched to 25 of the target genes whose expression was differential during microarray analysis, some of which were putatively negatively regulated by NifA. For selected genes, differential expression was corroborated by real time RT-PCR studies. Conclusion/Significance Our data suggest that life under conditions of nitrogen fixation is an important part of the lifestyle of strain BH72 in roots, as a wide range of genes far beyond the nif regulon is modulated. Moreover, the NifA regulon in strain BH72 appears to encompass a wider range of cellular functions

  7. Plant Growth-Promoting Rhizobacteria Inoculation to Enhance Vegetative Growth, Nitrogen Fixation and Nitrogen Remobilisation of Maize under Greenhouse Conditions.

    PubMed

    Kuan, Khing Boon; Othman, Radziah; Abdul Rahim, Khairuddin; Shamsuddin, Zulkifli H

    2016-01-01

    Plant growth-promoting rhizobacteria (PGPR) may provide a biological alternative to fix atmospheric N2 and delay N remobilisation in maize plant to increase crop yield, based on an understanding that plant-N remobilisation is directly correlated to its plant senescence. Thus, four PGPR strains were selected from a series of bacterial strains isolated from maize roots at two locations in Malaysia. The PGPR strains were screened in vitro for their biochemical plant growth-promoting (PGP) abilities and plant growth promotion assays. These strains were identified as Klebsiella sp. Br1, Klebsiella pneumoniae Fr1, Bacillus pumilus S1r1 and Acinetobacter sp. S3r2 and a reference strain used was Bacillus subtilis UPMB10. All the PGPR strains were tested positive for N2 fixation, phosphate solubilisation and auxin production by in vitro tests. In a greenhouse experiment with reduced fertiliser-N input (a third of recommended fertiliser-N rate), the N2 fixation abilities of PGPR in association with maize were determined by 15N isotope dilution technique at two harvests, namely, prior to anthesis (D50) and ear harvest (D65). The results indicated that dry biomass of top, root and ear, total N content and bacterial colonisations in non-rhizosphere, rhizosphere and endosphere of maize roots were influenced by PGPR inoculation. In particular, the plants inoculated with B. pumilus S1r1 generally outperformed those with the other treatments. They produced the highest N2 fixing capacity of 30.5% (262 mg N2 fixed plant-1) and 25.5% (304 mg N2 fixed plant-1) of the total N requirement of maize top at D50 and D65, respectively. N remobilisation and plant senescence in maize were delayed by PGPR inoculation, which is an indicative of greater grain production. This is indicated by significant interactions between PGPR strains and time of harvests for parameters on N uptake and at. % 15Ne of tassel. The phenomenon is also supported by the lower N content in tassels of maize treated with

  8. Plant Growth-Promoting Rhizobacteria Inoculation to Enhance Vegetative Growth, Nitrogen Fixation and Nitrogen Remobilisation of Maize under Greenhouse Conditions

    PubMed Central

    Kuan, Khing Boon; Othman, Radziah; Abdul Rahim, Khairuddin; Shamsuddin, Zulkifli H.

    2016-01-01

    Plant growth-promoting rhizobacteria (PGPR) may provide a biological alternative to fix atmospheric N2 and delay N remobilisation in maize plant to increase crop yield, based on an understanding that plant-N remobilisation is directly correlated to its plant senescence. Thus, four PGPR strains were selected from a series of bacterial strains isolated from maize roots at two locations in Malaysia. The PGPR strains were screened in vitro for their biochemical plant growth-promoting (PGP) abilities and plant growth promotion assays. These strains were identified as Klebsiella sp. Br1, Klebsiella pneumoniae Fr1, Bacillus pumilus S1r1 and Acinetobacter sp. S3r2 and a reference strain used was Bacillus subtilis UPMB10. All the PGPR strains were tested positive for N2 fixation, phosphate solubilisation and auxin production by in vitro tests. In a greenhouse experiment with reduced fertiliser-N input (a third of recommended fertiliser-N rate), the N2 fixation abilities of PGPR in association with maize were determined by 15N isotope dilution technique at two harvests, namely, prior to anthesis (D50) and ear harvest (D65). The results indicated that dry biomass of top, root and ear, total N content and bacterial colonisations in non-rhizosphere, rhizosphere and endosphere of maize roots were influenced by PGPR inoculation. In particular, the plants inoculated with B. pumilus S1r1 generally outperformed those with the other treatments. They produced the highest N2 fixing capacity of 30.5% (262 mg N2 fixed plant−1) and 25.5% (304 mg N2 fixed plant−1) of the total N requirement of maize top at D50 and D65, respectively. N remobilisation and plant senescence in maize were delayed by PGPR inoculation, which is an indicative of greater grain production. This is indicated by significant interactions between PGPR strains and time of harvests for parameters on N uptake and at. % 15Ne of tassel. The phenomenon is also supported by the lower N content in tassels of maize treated

  9. Contrasted Reactivity to Oxygen Tensions in Frankia sp. Strain CcI3 throughout Nitrogen Fixation and Assimilation

    PubMed Central

    Ghodhbane-Gtari, Faten; Hezbri, Karima; Ktari, Amir; Sbissi, Imed; Beauchemin, Nicholas; Gtari, Maher; Tisa, Louis S.

    2014-01-01

    Reconciling the irreconcilable is a primary struggle in aerobic nitrogen-fixing bacteria. Although nitrogenase is oxygen and reactive oxygen species-labile, oxygen tension is required to sustain respiration. In the nitrogen-fixing Frankia, various strategies have been developed through evolution to control the respiration and nitrogen-fixation balance. Here, we assessed the effect of different oxygen tensions on Frankia sp. strain CcI3 growth, vesicle production, and gene expression under different oxygen tensions. Both biomass and vesicle production were correlated with elevated oxygen levels under both nitrogen-replete and nitrogen-deficient conditions. The mRNA levels for the nitrogenase structural genes (nifHDK) were high under hypoxic and hyperoxic conditions compared to oxic conditions. The mRNA level for the hopanoid biosynthesis genes (sqhC and hpnC) was also elevated under hyperoxic conditions suggesting an increase in the vesicle envelope. Under nitrogen-deficient conditions, the hup2 mRNA levels increased with hyperoxic environment, while hup1 mRNA levels remained relatively constant. Taken together, these results indicate that Frankia protects nitrogenase by the use of multiple mechanisms including the vesicle-hopanoid barrier and increased respiratory protection. PMID:24987692

  10. Contrasted reactivity to oxygen tensions in Frankia sp. strain CcI3 throughout nitrogen fixation and assimilation.

    PubMed

    Ghodhbane-Gtari, Faten; Hezbri, Karima; Ktari, Amir; Sbissi, Imed; Beauchemin, Nicholas; Gtari, Maher; Tisa, Louis S

    2014-01-01

    Reconciling the irreconcilable is a primary struggle in aerobic nitrogen-fixing bacteria. Although nitrogenase is oxygen and reactive oxygen species-labile, oxygen tension is required to sustain respiration. In the nitrogen-fixing Frankia, various strategies have been developed through evolution to control the respiration and nitrogen-fixation balance. Here, we assessed the effect of different oxygen tensions on Frankia sp. strain CcI3 growth, vesicle production, and gene expression under different oxygen tensions. Both biomass and vesicle production were correlated with elevated oxygen levels under both nitrogen-replete and nitrogen-deficient conditions. The mRNA levels for the nitrogenase structural genes (nifHDK) were high under hypoxic and hyperoxic conditions compared to oxic conditions. The mRNA level for the hopanoid biosynthesis genes (sqhC and hpnC) was also elevated under hyperoxic conditions suggesting an increase in the vesicle envelope. Under nitrogen-deficient conditions, the hup2 mRNA levels increased with hyperoxic environment, while hup1 mRNA levels remained relatively constant. Taken together, these results indicate that Frankia protects nitrogenase by the use of multiple mechanisms including the vesicle-hopanoid barrier and increased respiratory protection. PMID:24987692