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PubMed1985

[Energy supply for nitrogen fixation of Anabaena sp. CH1 and CH2].

Energy needed for nitrogen fixation in Anabaena sp. has been studied. It was found that energy produced from photosynthesis but not from respiration was the main source for nitrogen fixation of Anabaena sp. CH1. In strain CH2, both photosynthesis and respiration supplied energy for nitrogen fixation. Some respiratory enzyme activities (IDH, MDH) were also higher in vegetative cells of strain CH2 than of strain CH1.

Cyanobacteria↗

PubMed1977

Energy requirement for symbiotic nitrogen fixation.

Comparing the energy required by legumes for symbiotic nitrogen fixation with that of assimilation of nitrate, Gibson concluded the costs to be about the same. About 15% of net photosynthetic production by the plant may be used in meeting its nitrogen requirements. If energy for the fixation of nitrogen symbiotically and that for the assimilation of NH4+ or NO3- from the soil solution are both provided by the chemical products of photosynthesis, then the CO2 respired in supplying that energy must contribute to the total efflux of CO2 from the plant in the dark. McCree and Thornley have discussed methods of partitioning the dark CO2 efflux into a growth (synthesis) and a maintenance component. Both nitrogen fixation and nitrogen assimilation can be expected to contribute to the CO2 flux associated with synthesis. If Gibson is correct, nodulated plants using only symbiotically fixed nitrogen should have the same growth coefficient as non-nodulated plants supplied with exogenous mineral nitrogen when grown in the same conditions. I have examined this hypothesis using a modification of the method used by McCree with Trifolium subterraneum L. cultivar Woogenellup as test material.

Carbon Dioxide↗

PubMed1970

Biological nitrogen fixation in Lake Erie.

Biological nitrogen fixation, as determined by acetylene reduction, occurs in Lake Erie. Fixation potential by blue-green algae in situ in water and by bacteria in collected sediments was demonstrated. Nitrogen-fixing activity occurred from June through November suggesting that it is significant over the extremes of seasonal variation in light, temperature, and nutrients.

Acetylene↗

PubMed1999

Phylogenetic diversity of nitrogen fixation genes in the symbiotic microbial community in the gut of diverse termites.

Nitrogen fixation by the microorganisms in the gut of termites is one of the crucial aspects of symbiosis, since termites usually thrive on a nitrogen-poor diet. The phylogenetic diversity of the nitrogen-fixing organisms within the symbiotic community in the guts of various termite species was investigated without culturing the resident microorganisms. A portion of the dinitrogenase reductase gene (nifH) was directly amplified from DNA extracted from the mixed population in the termite gut. Analysis of deduced amino acid sequences of the products of the clonally isolated nifH genes revealed the presence of diverse nifH sequences in most of the individual termite species, and their constituents were considerably different among termite species. A majority of the nifH sequences from six lower termites, which showed significant levels of nitrogen fixation activity, could be assigned to either the anaerobic nif group (consisting of clostridia and sulfur reducers) or the alternative nif methanogen group among the nifH phylogenetic groups. In the case of three higher termites, which showed only low levels of nitrogen fixation activity, a large number of the sequences were assigned to the most divergent nif group, probably functioning in some process other than nitrogen fixation and being derived from methanogenic archaea. The nifH groups detected were similar within each termite family but different among the termite families, suggesting an evolutionary trend reflecting the diazotrophic habitats in the symbiotic community. Within these phylogenetic groups, the sequences from the termites formed lineages distinct from those previously recognized in studies using classical microbiological techniques, and several sequence clusters unique to termites were found. The results indicate the presence of diverse potentially nitrogen-fixing microbial assemblages in the guts of termites, and the majority of them are as yet uncharacterized.

Animals↗

PubMed2000

Excitation energy transfer from phycobilisomes to photosystems: a phenomenon associated with the temporal separation of photosynthesis and nitrogen fixation in a cyanobacterium, Plectonema boryanum.

Plectonema boryanum shows temporal separation of photosynthesis and nitrogen fixation under diazotrophic conditions. Low temperature fluorescence studies have shown that in vivo the nitrogen fixing and photosynthesizing cells are adapted to 'state 2' and 'state 1', respectively. During nitrogen fixation phycobilisomes seem to transfer excitation energy to photosystem I whereas during oxygenic photosynthesis the energy is transferred to photosystem II. The state 2 adapted N-phase cells failed to undergo transition to state 1 while P-phase cells exhibited state 1 to state 2 transition. The nitrogen fixing cells showed a decreased level ofpsbC transcript, lack of CP47 in thylakoid membrane, and presence of the F685 peak but absence of the F695 peak in 77 K fluorescence spectra. These results suggest that the metabolic and molecular changes associated with nitrogen fixation may favor direct energy transfer from the phycobilisomes to photosystem I. This should help the organism to achieve low photosystem II and high photosystem I activity to set temporal separation of nitrogen fixation and photosynthesis for photoautotrophic growth under diazotrophic conditions.

Bacterial Proteins↗

PubMedDate not supplied

Simulating interactive effects of symbiotic nitrogen fixation, carbon dioxide elevation, and climatic change on legume growth.

The underlying mechanisms of interaction between the symbiotic nitrogen-fixation process and main physiological processes, such as assimilation, nutrient allocation, and structural growth, as well as effects of nitrogen fixation on plant responses to global change, are important and still open to more investigation. Appropriate models have not been adequately developed. A dynamic ecophysiological model was developed in this study for a legume plant [Glycine max (L.) Merr.] growing in northern China. The model synthesized symbiotic nitrogen fixation and the main physiological processes under variable atmospheric CO2 concentration and climatic conditions, and emphasized the interactive effects of these processes on seasonal biomass dynamics of the plant. Experimental measurements of ecophysiological quantities obtained in a CO2 enrichment experiment on soybean plants, were used to parameterize and validate the model. The results indicated that the model simulated the experiments with reasonable accuracy. The R2 values between simulations and observations are 0.94, 0.95, and 0.86 for total biomass, green biomass, and nodule biomass, respectively. The simulations for various combinations of atmospheric CO2 concentration, precipitation, and temperature, with or without nitrogen fixation, showed that increasing atmospheric CO2 concentration, precipitation, and efficiency of nitrogen fixation all have positive effects on biomass accumulation. On the other hand, an increased temperature induced lower rates of biomass accumulation under semi-arid conditions. In general, factors with positive effects on plant growth tended to promote each other in the simulation range, except the relationship between CO2 concentration and climatic factors. Because of the enhanced water use efficiency with a higher CO2 concentration, more significant effects of CO2 concentration were associated with a worse (dryer and warmer in this study) climate.

Biomass↗

PubMed2001

The disruption of a gene encoding a putative arylesterase impairs pyruvate dehydrogenase complex activity and nitrogen fixation in Sinorhizobium meliloti.

Nitrogen-fixing Sinorhizobium meliloti cells depend upon dicarboxylic acids as carbon and energy sources. The metabolism of these intermediate compounds of the trichloroacetic acid cycle is dependent upon the availability of acetyl-coenzyme A (CoA). In bacteroids, the combined activities of malic enzymes and pyruvate dehydrogenase (PDH) have been proposed to be responsible for the anaplerotic synthesis of acetyl-CoA. We obtained a S. meliloti mutant strain, PD3, in which a Tn5 insertion led to a significant decrease in the overall PDH activity. The genetic characterization of this mutant revealed that the transposon is located at the 3' end of a gene (ada) encoding a putative arylesterase. The mutant PD3 is deficient in nitrogen fixation, which strengthens the physiological importance of PDH activity in the symbiosis of S. meliloti with alfalfa plants.

Acetyl Coenzyme A↗

PubMed2001

Effects of trifluralin on soil microbial populations and the nitrogen fixation activities.

Effects of trifluralin on soil microbial populations and the nitrogen fixation activity of nitrogen-fixing bacteria Azotobacter chroococcum and Bradyrhizobium japonicum and the decomposition of trifluralin by soil microorganisms were studied. Trifluralin at lower concentrations from 0.5 mg microg(-1) dry soil to lower than 10.0 mg microg(-1) dry soil appeared to stimulate the growth of soil bacteria, actinomycetes, mould, and the pure cultures of Br. japonicum and A. chroococcum. Not only the colony amounts of these two species of nitrogen-fixing bacteria increased, grown on agar medium containing lower concentrations of trifluralin, but also these colonies also enlarged in size and appeared obviously in shorter formation time. However, trifluralin at higher concentrations would inhibit the development of microbial colonies both in amount and size. Trifluralin inhibited the activity of acetylene reduction of A. chroococcum when it was added at the same time of inoculation with A. chroococcum, but it showed a noteworthy stimulation to nitrogen fixation of A.chroococcum when it was put into culture after the cells of the nitrogen-fixing bacterium had grown well. The observation that soil microorganisms could use trifluralin as sole carbon and nitrogen resources for their growth, indicated that microorganisms could decompose trifluralin well.

Azotobacter↗

PubMed1981

Effect of growth-promoting chemicals on growth, nitrogen fixation and heterocyst frequency of a blue-green alga.

IAA was found to stimulate growth, nitrogen fixation and pigment synthesis in Anabaena doliolum in all concentrations tested. Heterocyst frequency was stimulated up to a concentration of 50 ppm IAA. NAA stimulated growth and nitrogen fixation up to 10 ppm. GA promoted growth, pigment synthesis, heterocyst frequency and nitrogen fixation only up to a concentration of 2 ppm. Kinetin promoted growth up to 100 ppm and synthesis of pigments, while nitrogen fixation was stimulated up to 5 ppm.

Chlorophyll↗

PubMed2001

Sulphate reduction and nitrogen fixation rates associated with roots, rhizomes and sediments from Zostera noltii and Spartina maritima meadows.

Sulphate reduction rates (SRR) and nitrogen fixation rates (NFR) associated with isolated roots, rhizomes and sediment from the rhizosphere of the marine macrophytes Zostera noltii and Spartina maritima, and the presence and distribution of Bacteria on the roots and rhizomes, were investigated. Between 1% and 3% of the surface area of the roots and rhizomes of both macrophytes were colonized by Bacteria. Bacteria on the surfaces of S. maritima roots and rhizomes were evenly distributed, while the distribution of Bacteria on Z. noltii roots and rhizomes was patchy. Root- and rhizome-associated SRR and NFR were always higher than rates in the bulk sediment. In particular, nitrogen fixation associated with the roots and rhizomes was 41-650-fold higher than in the bulk sediment. Despite the fact that sulphate reduction was elevated on roots and rhizomes compared with bulk sediment, the contribution of plant-associated sulphate reduction to overall sulphate reduction was small (< or =11%). In contrast, nitrogen fixation associated with the roots and rhizomes accounted for 31% and 91% of the nitrogen fixed in the rhizosphere of Z. noltii and S. maritima respectively. In addition, plant-associated nitrogen fixation could supply 37-1,613% of the nitrogen needed by the sulphate-reducing community. Sucrose stimulated nitrogen fixation and sulphate reduction significantly in the root and rhizome compartments of both macrophytes, but not in the bulk sediment.

Acetylene↗

PubMed1975

Diurnal variation in algal acetylene reduction (nitrogen fixation) in situ.

Diurnal variation in algal nitrogen fixation was studied in Lake Mendota, Wisconsin, during the summers of 1971 to 1973. Approximately two-thirds of the daily acetylene reduction in the surface decimeter occurred before noon. The decline in acetylene reduction (nmoles/liter.hr) near midday was partially because the algae relocated themselves at greater depths. However, acetylene reducing activity (nmoles per A(663) unit chlorophyll a per hour) also decreased as midday approached. Occasionally algae would resurface near the end of the day. On average, acetylene reduction (nmoles per liter per hour) was maximum at about 0900 Central standard time in the top decimeter, and acetylene reduction between 0830 and 0930 Central standard time represented 13% of the total daily acetylene reduction. Furthermore, acetylene reduction in the top decimeter, on average, represented 3.6% of the total acetylene reduction in the column. Calculation of the contribution by nitrogen fixation to a lake's fixed nitrogen budget is discussed.

Journal Article↗

PubMed1979

Effect of interactions among algae on nitrogen fixation by blue-green algae (cyanobacteria) in flooded soils.

Nitrogen fixation (C(2)H(2) 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.

Journal Article↗

PubMed1986

[Rhodopseudomonas sphaeroides mutants defective in nitrogen fixation].

Mutants of phototrophic bacterium Rhodopseudomonas sphaeroides deficient in nitrogen fixation and unable to utilize alanine, proline, arganine and glutamic acid as nitrogen sources have been obtained as a result of nitrosomethylurea mutagenesis. The majority of the nif-mutants have no nitrogenase activity and aminotransferase activity of glutamine synthetase during their growth in glutamine containing medium is sharply lowered. The specific activity of glutamate synthase and alanine dehydrogenase in the mutants does not differ from that of the wild type strain. One of the mutants (NF-42) has higher glutamine synthetase activity in comparison with the wild type strain. The pleiotropic character of the changes obtained in the nif-mutants shows that the loss of nitrogen fixation ability is due to defects in regulation system of nitrogen metabolism.

Culture Media↗

PubMed2005

Enterobacteria-mediated nitrogen fixation in natural populations of the fruit fly Ceratitis capitata.

Nitrogen, although abundant in the atmosphere, is paradoxically a limited resource for multicellular organisms. In the Animalia, biological nitrogen fixation has solely been demonstrated in termites. We found that all individuals of field-collected Mediterranean fruit flies (Ceratitis capitata) harbour large diazotrophic enterobacterial populations that express dinitrogen reductase in the gut. Moreover, nitrogen fixation was demonstrated in isolated guts and in live flies and may significantly contribute to the fly's nitrogen intake. The presence of similar bacterial consortia in additional insect orders suggests that nitrogen fixation occurs in vast pools of terrestrial insects. On such a large scale, this phenomenon may have a considerable impact on the nitrogen cycle.

Animals↗

PubMed2000

Excitation energy transfer from phycobilisomes to photosystems: a phenomenon associated with the temporal separation of photosynthesis and nitrogen fixation in a cyanobacterium, Plectonema boryanum(1).

Plectonema boryanum shows temporal separation of photosynthesis and nitrogen fixation under diazotrophic conditions. Low temperature fluorescence studies have shown that in vivo the nitrogen fixing and photosynthesizing cells are adapted to 'state 2' and 'state 1', respectively. During nitrogen fixation phycobilisomes seem to transfer excitation energy to photosystem I whereas during oxygenic photosynthesis the energy is transferred to photosystem II. The state 2 adapted N-phase cells failed to undergo transition to state 1 while P-phase cells exhibited state 1 to state 2 transition. The nitrogen fixing cells showed a decreased level of psbC transcript, lack of CP47 in thylakoid membrane, and presence of the F685 peak but absence of the F695 peak in 77 K fluorescence spectra. These results suggest that the metabolic and molecular changes associated with nitrogen fixation may favor direct energy transfer from the phycobilisomes to photosystem I. This should help the organism to achieve low photosystem II and high photosystem I activity to set temporal separation of nitrogen fixation and photosynthesis for photoautotrophic growth under diazotrophic conditions.

Journal Article↗

PubMedDate not supplied

[Nonsymbiotic nitrogen fixation in the podzolic soils of the Kola Peninsula].

Non-symbiotic nitrogen fixation was studied in virgin and cultivated podzol soils of the Kola Peninsula by the acetylene and isotope techniques. The activity of nitrogen fixation varied sharply in cultivated soils due to degradation of plant residues and the action of plant root secretion. No significant changes were observed in the activity of nitrogen fixation within the vegetative period in virgin soils. Less than 1 kg of nitrogen per hectare was accumulated in soils as a result of its non-symbiotic fixation during the vegetative periods of 1976--1977.

Aerobiosis↗

PubMed1982

Molecular cloning of Rhizobium trifolii genes involved in symbiotic nitrogen fixation.

DNA sequences responsible for the development and maintenance of symbiotic nitrogen fixation have been identified and isolated from Rhizobium trifolii. Symbiotically-defective strains were generated by random mutagenesis with the transposon Tn5. The defective genes which give rise to the mutant phenotype have been cloned into bacterial plasmids and used as hybridization probes to isolate the corresponding wild-type genes from a clone bank of R. trifolii DNA. Symbiotic genes cloned in this manner are able to correct the lesion caused by the insertion of the transposon in their respective mutants and so restore the nitrogen fixation phenotype. The correction of the mutation is shown to occur by two distinguishable mechanisms--either by complementation or by homologous recombination. This approach provides a reliable method for isolation and mapping of bacterial DNA sequences involved in symbiotic nitrogen fixation.

Cloning, Molecular↗

PubMed1978

Involvement of the cytoplasmic membrane in nitrogen fixation by Rhizobium leguminosarum bacteroids.

1. The nitrogen-fixing efficiency of freshly prepared suspensions of Rhizobium leguminosarum bacteroids from pea root nodules was considerably enhanced by addition of bovine serum albumin. Evidence was found that during preparation of bacteroids the cell membrane is exposed to the uncoupling effect of free fatty acids and to plant phospholipase D activity. Both effects could be counteracted by bovine serum albumin. 2. A technique was developed by which concentrations of free O2 and nitrogenase activity could be measured simultaneously under conditions of steady-state respiration. By means of this system it could be shown that in contrast to previous claims, high ATP/ADP ratios can be achieved in bacteroids even with a high concentration of O2 in the medium. 3. Nitrogen fixation was found to be controlled by the ATP/ADP ratio, the generation of reducing equivalents and the switch-off phenomenon. It was demonstrated that the generation of reducing equivalents for nitrogenase is regulated by the energized state and the integrity of the bacteroid cell membrane. The data indicate that the process of aerobic nitrogen fixation in R. leguminosarum bacteroids resembles that of Azotobacter vinelandii.

Adenosine Diphosphate↗