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Results for “NITROGEN FIXATION”

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At least 127 records · Page 7Linked to original sources

PubMed1980

Identification of blue-green algal nitrogen fixation genes by using heterologous DNA hybridization probes.

In the filamentous blue-green alga Anabaena 7120, aerobic nitrogen fixation is linked to the differentiation of specialized cells called heterocysts. In order to study control of heterocyst development and nitrogen fixation in Anabaena, we have used cloned fragments of the Klebsiella pneumoniae nitrogen fixation (nif) genes as probes in DNA.DNA hybridizations with restriction endonuclease fragments of Anabaena DNA. Using this technique, we were able to identify and clone Anabaena nif genes, demonstrating the feasibility of using heterologous probes to identify genes for which no traditional genetic selection exists. From the patterns of hybridization observed, we deduced that although DNA sequence homology has been retained between some of the nif genes of these divergent organisms, the nif gene order has been rearranged.

Journal Article↗

PubMed1977

Nitrogen fixation by Spirillum sp. from rice roots.

Nitrogen fixation by Spirillum sp. obtained from the roots of rice plants grown at different levels of combined nitrogen was studied. The roots of rice plants exposed to low levels of combined nitrogen (20--40 kg N/ha) harboured Spirillum sp. possessing higher nitrogen-fixing efficiency as compared to the cultures from plants receiving 60--100 kg N/ha. Moreover, the nitrogen-fixing efficiency of these Spirillum spp. varied with age of the plant, irrespective of the dosage of combined nitrogen.

Fertilizers↗

PubMed2004

Iron and phosphorus co-limit nitrogen fixation in the eastern tropical North Atlantic.

The role of iron in enhancing phytoplankton productivity in high nutrient, low chlorophyll oceanic regions was demonstrated first through iron-addition bioassay experiments and subsequently confirmed by large-scale iron fertilization experiments. Iron supply has been hypothesized to limit nitrogen fixation and hence oceanic primary productivity on geological timescales, providing an alternative to phosphorus as the ultimate limiting nutrient. Oceanographic observations have been interpreted both to confirm and refute this hypothesis, but direct experimental evidence is lacking. We conducted experiments to test this hypothesis during the Meteor 55 cruise to the tropical North Atlantic. This region is rich in diazotrophs and strongly impacted by Saharan dust input. Here we show that community primary productivity was nitrogen-limited, and that nitrogen fixation was co-limited by iron and phosphorus. Saharan dust addition stimulated nitrogen fixation, presumably by supplying both iron and phosphorus. Our results support the hypothesis that aeolian mineral dust deposition promotes nitrogen fixation in the eastern tropical North Atlantic.

Animals↗

PubMed2002

The Rhizobium etli gene iscN is highly expressed in bacteroids and required for nitrogen fixation.

Sequence analysis of the rpoN (2)- fixA intergenic region in the genome of Rhizobium etli CNPAF512 has uncovered three genes involved in nitrogen fixation, namely nifU, nifS and nifW. These genes are preceded by an ORF that is highly conserved among nitrogen-fixing bacteria. It encodes a putative gene product of 105 amino acids, belonging to the HesB-like protein family. A phylogenetic analysis of members of the HesB-like protein family showed that the R. etli HesB-like protein clusters with polypeptides encoded by ORFs situated upstream of the nifUS nitrogen fixation regions in the genomes of other diazotrophs. The R. etli ORF that encodes the HesB-like protein was designated iscN. iscN is co-transcribed with nifU and nifS, and is preferentially expressed under free-living microaerobic conditions and in bacteroids. Expression is regulated by the alternative sigma factor RpoN and the enchancer-binding protein NifA. A R. etli iscN mutant displays a reduction in nitrogen fixation capacity of 90% compared to the wild-type strain. This Nif(-) phenotype could be complemented by the introduction of intact copies of R. etli iscN.

Acetylene↗

PubMed2001

Abscisic acid induces a decline in nitrogen fixation that involves leghaemoglobin, but is independent of sucrose synthase activity.

Sucrose synthase (SS) activity has been suggested to be a key point of regulation in nodule metabolism since this enzyme is down-regulated in response to different stresses which lead to decreased nitrogen fixation. In soybean, a dramatic decline of SS transcripts has been observed within 1 d from the onset of drought. Such a quick response suggests mediation by a signal transduction molecule. Abscisic acid (ABA) is a likely candidate to act as such a molecule as it mediates in a significant number of plant responses to environmental constraints. The hypothesis of ABA controlling nodule metabolism was approached in this work by assessing nodule responses to exogenous ABA supply in pea. Under the experimental conditions, ABA did not affect plant biomass, nodule numbers or dry weight. However, nitrogen fixation rate was reduced by 70% within 5 d and by 80% after 9 d leading to a reduced plant organic nitrogen content. Leghaemoglobin (Lb) content declined in parallel with that of nitrogen fixation. SS activity, however, was not affected by ABA treatment, and neither were the activities of the enzymes aspartate amino transferase, alkaline invertase, malate dehydrogenase, glutamate synthase, uridine diphosphoglucose pyrophosphorylase, isocitrate dehydrogenase, and glutamine synthetase. Nodule bacteroid-soluble protein content was reduced in nodules only after 9 d of ABA treatment. These results do not support the hypothesis that ABA directly regulates SS activity. However, they do suggest the occurrence of at least two different control pathways in nodules under environmental constraints, which include ABA being involved in a Lb/oxygen-related control of nitrogen fixation.

Abscisic Acid↗

PubMed1978

Effects of some inorganic elements on nitrogen-fixation in blue-green algae and some ecological aspects of pollution.

Nitrogen-fixation by two species of Nostoc, one of them a lichen phycobiont, was generally stimulated by low concentrations of arsenic, cadmium, nickel, lead, palladium, and zinc. Higher concentrations (0.025 to 0.125 ppm) of arsenic, nickel, and palladium were also stimulatory; however, higher concentrations of cadmium, lead, and zinc tended to inhibit fixation. With the exception of palladium and zinc at low concentrations these six tested elements tended to inhibit nitrogen-fixation in Chlorogloea fritschii and Westiellopsis sp.

Arsenic↗

PubMed1986

Comparison of Two Cellulomonas Strains and Their Interaction with Azospirillum brasilense in Degradation of Wheat Straw and Associated Nitrogen Fixation.

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 CSI-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(2)H(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.

Journal Article↗

PubMed2001

Microbiological, molecular biological and stable isotopic evidence for nitrogen fixation in the open waters of Lake Michigan.

We have used a combination of microbiological, molecular biological and stable isotope methods to relate specific microbial populations to elemental cycling at an offshore site in Lake Michigan. Several lines of evidence suggest that atmospheric N2 may be a significant source of nitrogen to the lake. Particulate organic nitrogen (PON) at approximately equals 10-15m depth in July and October had a delta15N of 0.5-1.5%o. These values closely reflect the 15N composition of atmospheric N2, suggesting biological nitrogen fixation. Historical data show a developing late-summer N:P minimum at approximately equals 15 m; low abundance of inorganic nitrogen relative to phosphorus favours species able to acquire atmospheric nitrogen. Microscopic examination of October water samples revealed abundant heterocystous cyanobacteria, including Nodularia sp. Potentially nitrogen-fixing Anabaena spp. have been found in Lake Michigan before but, to our knowledge, this is the first report of Nodularia. Finally, we have amplified both cyanobacterial and non-cyanobacterial nifH sequences (encoding the nitrogenase iron protein) from lakewater samples, evidence for the presence of bacteria capable of nitrogen fixation. The surface waters of Lake Michigan are considered to be phosphate limited in the stratified season and, under these conditions, energetically expensive nitrogen fixation is expected to be uncompetitive with assimilation of combined nitrogen. Our results suggest that, from both microbiological and biogeochemical perspectives, this may be an oversimplification.

Animals↗

PubMedDate not supplied

[Molecular nitrogen fixation in the waters of eutrophic and polyhuic lakes of the Estonian SSR].

A modified acetylene technique was used to assay the rate of molecular nitrogen fixation in Estonian lakes containing methane in the hypolimnion. Methods were elaborated to eliminate ethylene cooxidation by methane oxidizing bacteria. Methane oxidation and nitrogen fixation were found in a narrow microaerobic zone in lakes with the stratification of temperature in the water mass; these biochemical processes occurred when the content of dissolved oxygen varied within the range of 0.1 to 0.8 mg O2 per litre. The rate of these microbiological processes was significantly influenced by trophic relationships with microorganisms from the adjacent ecological niches. In the epilmnion of eutrophic lakes, atmospheric nitrogen was fixed by the blue-green algae Anabaena and Gloeocapsa minima and by the heterotrophic bacterium Azomonas agilis; in the microaerobic zone of metalimnion, atmospheric nitrogen was fixed by the methane oxidizing bacteria Methylosinus trichosporium and M. sporium and by the hydrogen oxidizing bacterium Mycobacterium flavum. In polyhumic lakes, nitrogen fixation was performed by the bactera Az. insignes, Methylosinus trichosporium, M. sporium and Mycobacterium flavum only in water layers near the bottom with microaerobic conditions.

Estonia↗

PubMed2005

The sulfate transporter SST1 is crucial for symbiotic nitrogen fixation in Lotus japonicus root nodules.

Symbiotic nitrogen fixation (SNF) by intracellular rhizobia within legume root nodules requires the exchange of nutrients between host plant cells and their resident bacteria. Little is known at the molecular level about plant transporters that mediate such exchanges. Several mutants of the model legume Lotus japonicus have been identified that develop nodules with metabolic defects that cannot fix nitrogen efficiently and exhibit retarded growth under symbiotic conditions. Map-based cloning of defective genes in two such mutants, sst1-1 and sst1-2 (for symbiotic sulfate transporter), revealed two alleles of the same gene. The gene is expressed in a nodule-specific manner and encodes a protein homologous with eukaryotic sulfate transporters. Full-length cDNA of the gene complemented a yeast mutant defective in sulfate transport. Hence, the gene was named Sst1. The sst1-1 and sst1-2 mutants exhibited normal growth and development under nonsymbiotic growth conditions, a result consistent with the nodule-specific expression of Sst1. Data from a previous proteomic study indicate that SST1 is located on the symbiosome membrane in Lotus nodules. Together, these results suggest that SST1 transports sulfate from the plant cell cytoplasm to the intracellular rhizobia, where the nutrient is essential for protein and cofactor synthesis, including nitrogenase biosynthesis. This work shows the importance of plant sulfate transport in SNF and the specialization of a eukaryotic transporter gene for this purpose.

Amino Acid Sequence↗

PubMed2003

Identification of three genes encoding P(II)-like proteins in Gluconacetobacter diazotrophicus: studies of their role(s) in the control of nitrogen fixation.

In our studies on the regulation of nitrogen metabolism in Gluconacetobacter diazotrophicus, an endophytic diazotroph of sugarcane, three glnB-like genes were identified and their role(s) in the control of nitrogen fixation was studied. Sequence analysis revealed that one P(II) protein-encoding gene, glnB, was adjacent to a glnA gene (encoding glutamine synthetase) and that two other P(II) protein-encoding genes, identified as glnK1 and glnK2, were located upstream of amtB1 and amtB2, respectively, genes which in other organisms encode ammonium (or methylammonium) transporters. Single and double mutants and a triple mutant with respect to the three P(II) protein-encoding genes were constructed, and the effects of the mutations on nitrogenase expression and activity in the presence of either ammonium starvation or ammonium sufficiency were studied. Based on the results presented here, it is suggested that none of the three P(II) homologs is required for nif gene expression, that the GlnK2 protein acts primarily as an inhibitor of nif gene expression, and that GlnB and GlnK1 control the expression of nif genes in response to ammonium availability, both directly and by relieving the inhibition by GlnK2. This model includes novel regulatory features of P(II) proteins.

Acetobacteraceae↗

PubMedDate not supplied

[Molecular nitrogen fixation in eutrophic Beloye Ozero].

The rate of production and mineralization of organic matter and the rate of fixation of molecular nitrogen were assayed in th eutrophic lake Beloye (near Moscow) at the end of summer stagnation (1976). The content of hydrogen sulphide reached 6.8 mg per litre which resulted in a change of the ecological environment in the lake. The fixation of molecular nitrogen in water layers was characterized by three maxima: 5.0 mcg N per litre per 4 hours (surface); 4.2 mcg N per litre per 4 hours (metalimnion) and 2.8 mcg N per litre per 4 hours (at bottom). The fixation of nitrogen in the trophogenous layer involved mainly the blue-green alga Anabaena. In the sulphide zone, molecular nitrogen was fixed by butyric and sulphate-reducing bacteria.

Cyanobacteria↗

PubMed1977

Complementation analysis of Klebsiella pneumoniae mutants defective in nitrogen fixation.

A series of mutants defective in nitrogen fixation (nif) were isolated in Klebsiella pneumoniae strain M5a1. The nif mutations were either located on plasmid pRD1 or on the K. pneumoniae chromosome. A total of 37 plasmid mutants and 28 chromosomal mutants were employed in complementation tests using the acetylene reduction technique. Most mutants could be assigned to one of seven nif cistrons: nifA, nifB, nifD, nifE, nifF, nifH, and nifK. Complementation analysis of two nif deletion mutants confirmed transductional evidence that these strains carry nifB-A-F deletions. One deletion mutant had, in contrast to previous transductional analysis, a functional nifK cistron and presumably is deleted for nifB-A-F-E. Examination of the biochemical phenotype of several mutants suggests that the nifA product has a regulatory function, and nifK, nifD and nifH are most probably the structural genes for nitrogenase.

Chromosomes, Bacterial↗

PubMedDate not supplied

[Seasonal fluctuations in the potential soil capacity for nitrogen fixation].

The nitrogenase activity of soils to which no energy-rich substances were added is low. This can be attributed to a low content of easily available organic substances. The potential activity of nitrogen fixation of the soils under study is different and changes with seasons. The highest ability for potential nitrogen fixation is displayed by soddy-calcareous and continuous-cultivated grey forest soils. The potential activity of nitrogen fixation in these soils correlates with the bacterial number on agar. Such a correlation is not observed in grey forest soils.

Ecology↗

PubMed2004

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

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 development of root systems that access groundwater to satisfy demands for both water and nutrients. This is an ecologically favourable strategy since only groundwater is a predictable and stable resource.

Atmosphere↗

PubMed2006

Simulated glyphosate drift influences nitrate assimilation and nitrogen fixation in non-glyphosate-resistant soybean.

Nontarget injury from glyphosate drift is a concern among growers using non-glyphosate-resistant (non-GR) cultivars. The effects of glyphosate drift on nitrate assimilation and nitrogen fixation potential, nodule mass, and yield of non-GR soybean were assessed in a field trial at Stoneville, MS. A non-GR soybean cultivar 'Delta Pine 4748S' was treated with glyphosate at 12.5% of use rate of 0.84 kg of active ingredient/ha at 3 (V2), 6 (V7), and 8 (R2, full bloom) weeks after planting (WAP) soybean to simulate glyphosate drift. Untreated soybean was used as a control. Soybeans were sampled weekly for 2 weeks after each glyphosate treatment to assess nitrate assimilation and N2 fixation potential. Nitrate assimilation was assessed using in vivo nitrate reductase assay in leaves, stems, roots, and nodules. Nitrogen fixation potential was assessed by measuring nitrogenase activity using the acetylene reduction assay (ARA). Nitrogen content of leaves, shoots, and seed and soybean yield were also determined. In the first sampling date (4 WAP), glyphosate drift caused a significant decrease in NRA in leaves (60%), stems (77%), and nodules (50%), with no decrease in roots. At later growth stages, NRA in leaves was more sensitive to glyphosate drift than stems and roots. Nitrogenase activity was reduced 36-58% by glyphosate treatment at 3 or 6 WAP. However, glyphosate treatment at 8 WAP had no effect on nitrogenase activity. Nitrogen content was affected by glyphosate application only in shoots after the first application. No yield, seed nitrogen, protein, or oil concentration differences were detected. These results suggest that nitrate assimilation and nitrogen fixation potential were significantly reduced by glyphosate drift, with the greatest sensitivity early in vegetative growth. Soybean has the ability to recover from the physiological stress caused by glyphosate drift.

Drug Resistance↗

PubMed2005

Nitrogen fixation: key genetic regulatory mechanisms.

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.

Azotobacter vinelandii↗

PubMed2002

Could microbial symbionts of arthropod guts contribute significantly to nitrogen fixation in terrestrial ecosystems?

Fixed nitrogen is a limiting nutrient in most terrestrial ecosystems and has been assumed to be supplied almost entirely by free-living bacteria as well as by bacteria living in association with plants. The survival and growth of many arthropods on diets with extremely high carbon to nitrogen (C:N) ratios suggest that these arthropods are not obtaining sufficient nitrogen from their diets but must be obtaining additional nitrogen from some other source(s). Estimates of N(2) fixation have suggested that symbiotic microbes of some arthropod hindguts could be obtaining this additional nitrogen as a result of nitrogen fixation. With the recent availability of antibody and nucleic acid probes, the presence of the enzyme that reduces dinitrogen gas to ammonia (nitrogenase) as well as the presence of its transcripts can be detected and localized with great sensitivity. A preliminary survey of a few detritivores indicates that nitrogen-fixing microbes of diverse forms are widespread in arthropod hindguts. In calculating nitrogen budgets, the possible contributions of nitrogen fixation by symbionts in arthropod guts, however, has been largely ignored. N(2) fixation in arthropod guts, with rates as high as 10-40 kg/ha/year being possible, may represent a significant contribution both to the growth of arthropods and to their ecosystem functions of processing carbon and nitrogen.

Journal Article↗