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PubMed1979

Nitrate reductase activities of rhizobia and the correlation between nitrate reduction and nitrogen fixation.

All species of Rhizobium except R. lupini had nitrate reductase activity. Only R. lupini was incapable of growth with nitrate as the sole source of nitrogen. However, the conditions necessary for the induction of nitrate reductase varied among species of Rhizobium. Rhizobium japonicum and some Rhizobium species of the cowpea strains expressed nitrate reductase activities both in the root nodules of appropriate leguminous hosts and when grown in the presence of nitrate. Rhizobium trifolii, R. phaseoli, and R. leguminosarum did not express nitrate reductase activities in the root nodules, but they did express them when grown in the presence of nitrate. In bacteroids of R. japonicum and some strains of cowpea Rhizobium, high N2 fixation activities were accompanied by high nitrate reductase activities. In bacteroids of R. trifolii, R. leguminosarum, and R. phaseoli, high N2 fixation activities were not accompanied by high nitrate reductase activities.

Culture Media↗
PubMed1981

Effects of salinity on acetylene reduction (nitrogen fixation) and respiration in a marine azotobacter.

An acetylene-reducing (nitrogen-fixing) bacterium, identified as Azotobacter sp., was isolated from a site in the Canary Creek Marsh, Del. Acetylene reduction activity of the isolate was maximal at 15 to 25 per thousand NaCl, with no activity observed at 0 or 60 per thousand. Respiration studies showed similar results, with maximal activity occurring at a slightly lower salinity (10 to 20 per thousand NaCl). The salinities over which peak activity occurred fell within the normal range of in situ salinity (20 to 28 per thousand total salinity).

Journal Article↗
PubMed1993

Nitrogen fixation by the thermophilic green sulfur bacterium Chlorobium tepidum.

The thermophilic green sulfur bacterium Chlorobium tepidum grew with N2, NH4+, or glutamine as the sole nitrogen source under phototrophic (anaerobic-light) conditions. Growth on N2 required increased buffering capacity to stabilize uncharacterized pH changes that occurred during diazotrophic growth. Increased sulfide levels were stimulatory for growth on N2. Levels of nitrogenase activity (acetylene reduction) in N2-grown C. tepidum cells were very high, among the highest ever reported for anoxygenic phototrophic bacteria. Maximal acetylene reduction rates in C. tepidum cells were observed at 48 to 50 degrees C, which is about 15 degrees C higher than the optimum temperature for nitrogenase activity in mesophilic chlorobia, and nitrogenase activity in C. tepidum responded to addition of ammonia by a "switch-off/switch-on" mechanism like that in phototrophic purple bacteria. C. tepidum cells assimilated ammonia mainly via the glutamine synthetase-glutamate synthase pathway, elevated levels of both of these enzymes being present in cells grown on N2. These results show that N2 fixation can occur in green sulfur bacteria up to at least 60 degrees C and that regulatory mechanisms important in control of nitrogenase activity in mesophilic anoxygenic phototrophs also appear to regulate thermally active forms of the enzyme.

Ammonia↗
PubMed1986

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

Nitrate-grown Azotobacter chroococcum ATCC 4412 cells lack the ability to fix N2. 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 N2-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 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 antions, 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. We 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.

Azotobacter↗
PubMed2006

Nitrogen fixation and leaching of biological soil crust communities in mesic temperate soils.

Biological soil crust is composed of lichens, cyanobacteria, green algae, mosses, and fungi. Although crusts are a dominant source of nitrogen (N) in arid ecosystems, this study is among the first to demonstrate their contribution to N availability in xeric temperate habitats. The study site is located in Lucas County of Northwest Ohio. Using an acetylene reduction technique, we demonstrated potential N fixation for these crusts covering sandy, acidic, low N soil. Similar fixation rates were observed for crust whether dominated by moss, lichen, or bare soil. N inputs from biological crusts in northwestern Ohio are comparable to those in arid regions, but contribute substantially less N than by atmospheric deposition. Nitrate and ammonium leaching from the crust layer were quantified using ion exchange resin bags inserted within intact soil cores at 4 cm depth. Leaching of ammonium was greater and nitrate less in lichen than moss crusts or bare soil, and was less than that deposited from atmospheric sources. Therefore, biological crusts in these mesic, temperate soils may be immobilizing excess ammonium and nitrate that would otherwise be leached through the sandy soil. Moreover, automated monitoring of microclimate in the surface 7 cm of soil suggests that moisture and temperature fluctuations in soil are moderated under crust compared to bare soil without crust. We conclude that biological crusts in northwestern Ohio contribute potential N fixation, reduce N leaching, and moderate soil microclimate.

Biodegradation, Environmental↗
PubMed1984

Nitrogen Fixation in an Establishing Alfalfa (Medicago sativa L.) Ley in Sweden, Estimated by Three Different Methods.

In an investigation of the ability of alfalfa to fix nitrogen under field conditions in Scandinavia, N(2) fixation during the establishment year ranged between 7.85 and 10.37 g of N m, depending on the method used. The methods used were an in situ acetylene reduction method, a N isotope dilution method using two reference crops, and a total-N difference method. The dynamics of nitrogenase activity in relation to plant development was studied by using the acetylene reduction method. Also, the diurnal variation in N(2) fixation at the field site was studied with the acetylene reduction method; no diurnal change was detected, which is explained by the fact that the nodules within the soil were protected against short-term fluctuations in temperature. The significant amount of nitrogen fixed by alfalfa during its first year even at northern latitudes suggests that this crop offers an alternative to conventional field management of heavily fertilized nonlegume leys.

Journal Article↗
PubMed1979

Evidences suggestive of no intestinal nitrogen fixation for improving protein nutrition status in sweet potato eaters.

Total of seven teenagers and two adults were given sweet potato diets that supplied slightly below requirement levels of protein for 32 (experiment 1) or 53 days (experiment 2) in two separate experiments. In experiment 1 and during the first 36 days of experiment 2, nitrogen (N) balance studies with the teenagers were conducted with 0.67 and 0.71 g of protein per kilogram of body weight, respectively. Results of the N balances including skin N loss were -0.5 mg N/kg per day in experiment 1 and -3.2 mg N/kg per day in experiment 2. Two adults were given 0.63 g/kg of protein and gave average N balance of +6.0 mg N/kg per day (experiment 2), however, one of them had a slightly negative cumulative N balance if miscellaneous N losses were included in calculation. Plasma urea N of both teenagers and adults decreased significantly from 8 to 11 to 2 to 3 mg/100 ml in experiment 2. After 32 or 53 days on the sweet potato diets, the plasma free amino acid pattern of the teenager subjects showed abnormality. Furthermore, the subjects were easier to get fatigue by physical exercise, and took longer nap due to sleepiness during the latter days of the experiments. Thus, although the mean hemoglobin, hematocrit, plasma total protein, and plasma albumin levels were within the normal ranges, the protein nutrition status of the teenagers and one of the two adults was considered to be not normal. The results suggested that intestinal N-fixation that was proposed by several investigators to occur in sweet potato eaters probably did not occur. The subjects' feces were examined in vitro for the ability of N-fixation with negative results. During the last 17 days of experiment 2 the effect of excess calorie on N balance was examined.

Adolescent↗
PubMed1979

Nitrogen fixation by thermophilic blue-green algae (cyanobacteria): temperature characteristics and potential use in biophotolysis.

Thermophilic, nitrogen-fixing, blue-green algae (cyanobacteria) were investigated for use in biophotolysis. Three strains of Mastigocladus laminosus were tested and were found to be equally effective in biophotolysis as judged by nitrogenase activity. The alga, M. laminosus NZ-86-m, which was chosen for further study, grew well in the temperature range from 35 to 50 degrees C, with optimum growth at 45 degrees C, at which temperature acetylene reduction activity was also greatest. The maximum tolerable temperature was 55 degrees C. Acetylene reduction activity was saturated at a light intensity of 1 x 10 ergs cm s. Atmospheric oxygen tension was found to be slightly inhibitory to acetylene reduction of both slowly growing and exponentially growing cultures. Nonsterile continuous cultures, which were conducted to test problems of culture maintenance, could be operated for 2 months without any significant decrease in nitrogenase activity or contamination by other algae. Nitrogen-starved cultures of M. laminosus NZ-86-m produced hydrogen at comparable rates to Anabaena cylindrica. The conversion efficiency of light to hydrogen energy at maximum rates of hydrogen production was 2.7%.

Journal Article↗
PubMed1978

Microbial fixation of nitrogen in presence of lanthanum sulphate with sodium molybdate.

The effect of lanthanum sulphate together with 100 micrometer of sodium molybdate show that there is considerable increase in nitrogen fixation and carbon consumption in the culture medium of nitrogen-fixing Azotobacter species A1 and A2, isolated from Allahabad soil. But these combination decrease the nitrogen fixation and carbon consumption in case of another species, Azotobacter A3, of the same soil.

Azotobacter↗
PubMed1976

Acetylene reduction (nitrogen fixation) associated with corn inoculated with Spirillum.

Sorghum and corn breeding lines were grown in soil in field and greenhouse experiments with and without an inoculum of N2-fixing in Spirillum strains from Brazil. Estimated rates of N2 fixation associated with field-grown corn and sorghum plants were less than 4 g of N2/ha per day. The mean estimated N2-fixation rates determined on segments of roots from corn inoculated with Spirillum and grown in the greenhouse at 24 to 27 degrees C were 15 g of N2/ha per day (16 inbreds), 25 g of N2/ha per day (six hybrids), and 165 g of N2/ha per day for one hybird which was heavily inoculated. The corresponding mean rates determined from measurements of in situ cultures of the same series of corn plants (i.e., 16 inbreds, six hybrids, and one heavily inoculated hybrid) were 0.4, 2.3, and 1.1 g of N2/ha per day, respectively. Lower rates of C2H2 reduction were associated with control corn cultures which had been treated with autoclaved Spirillum than with cultures inoculated with live Spirillum. No C2H2 reduction was detected in plant cultures treated with ammonium nitrate. Numbers of nitrogen-fixing bacteria on excised roots of corn plants increased an average of about 30-fold during an overnight preincubation period, and as a result acetylene reduction assays of root samples after preincubation failed to serve as a valid basis for estimating N2 fixation by corn in pot cultures. Plants grown without added nitrogen either with or without inoculum exhibited severe symptoms of nitrogen deficiency and in most cases produced significantly less dry weight than those supplied with fixed nitrogen. Although substantial rates of C2H2 reduction by excised corn roots were observed after preincubation under limited oxygen, the yield and nitrogen content of inoculated plants and the C2H2-reduction rates by inoculated pot cultures of corn, in situ, provided no evidence of appreciable N2 fixation.

Acetylene↗
PubMed1981

Fungicide Enhancement of Nitrogen Fixation and Colonization of Phaseolus vulgaris by Rhizobium phaseoli.

The number and weight of pods and the weight and nitrogen content of the tops of beans (Phaseolus vulgaris) derived from seeds inoculated with a thiram-resistant strain of Rhizobium phaseoli were increased if the seeds were treated with thiram before sowing in soil. A greater percentage of the nodules on 21-day-old plants were derived from the resistant strain, more nodules were formed, and these nodules were more effective in the presence of the fungicide than in its absence. These differences in nodule numbers were no longer present in 56-day-old plants, and only a small percentage of the nodules contained the resistant strain. The abundance of the fungicide-tolerant R. phaseoli increased rapidly soon after planting the seed and subsequently fell markedly, but the rate of decline was less if the seeds had been treated with the chemical. Protozoa also proliferated if thiram had not been applied to the seed, but their numbers were deleteriously influenced by thiram. Bdellovibrio, bacteriophages, and lytic micro-organisms acting on R. phaseoli were rare under these conditions. Ciliates and flagellated protozoa were initially suppressed by planting thiram-coated bean seeds in nonsterile soil, but the former were inhibited longer than the latter and the ciliate numbers never fully recovered if the seeds were treated with the fungicide. The resistant strain grew well in sterile soil also inoculated with a protozoa-free mixture of soil microorganisms whether thiram was added or not, but after an initial rise in numbers, its abundance fell if the mixture contained protozoa; the rate of this fall was delayed by the fungicide. The numbers of R. phaseoli were consistently less in sterile soil inoculated with the rhizobium plus a mixture of soil microorganisms containing ciliates and other protozoa than if the inoculum contained other protozoa but no ciliates. These results suggest that a suppression of protozoa, and possibly especially the ciliates, accounts for the enhanced growth of beans and the greater initial frequency of nodules formed by the thiram-resistant R. phaseoli in the presence of this fungicide. Thiram applied to uninoculated seed enhanced bean growth if thiram-resistant R. phaseoli were present in soil.

Journal Article↗
PubMed1978

Simultaneous measurement of nitrogen fixation estimated by acetylene-ethylene assay and nitrate absorption by soybeans.

An apparatus was designed for simultaneous measurement of rates of N(2) fixation estimated by C(2)H(2)-C(2)H(4) assay (N(2)[C(2)H(2)] fixation) and NO(3) (-) absorption by roots of intact, nodulated soybeans (Glycine max [L.] Merr.). The principal design features include: (a) a gas-tight mist chamber in which nodulated roots can be exposed simultaneously to C(2)H(2) in the gas phase and to a liquid phase containing NO(3) (-) sprayed in a fine mist; and (b) provision for sampling the gas phase for C(2)H(4) determination, and the liquid phase for NO(3) (-) determination.We studied NO(3) (-) absorption by soybeans as affected by nodulation, NO(3) (-) concentration during assay, and previous N nutrition during growth in nutrient solution culture in controlled environment chambers. It was established that 0.5 mm NO(3) (-) nearly saturated the NO(3) (-) absorption system of both nodulated and unnodulated soybeans when the concentration dependence of NO(3) (-) absorption rate was measured just after flowering began. Nitrate absorption rates were measured after development of N stress in unnodulated plants, and during recovery from N stress in nodulated plants. The results suggested that the lower capacity for NO(3) (-) absorption of nodulated plants was a consequence of N stress during the period of nodule growth and development.Nitrogen [C(2)H(2)] fixation rates were compared in intact plants assayed in the mist chamber and in excised roots assayed in both the mist chamber and in glass jars. Excised roots had a lower N(2)[C(2)H(2)] fixation rate than intact plants. The decline observed during the first hour after shoot removal was more pronounced for glass jar-assayed excised roots than for mist chamber-assayed excised roots.We discuss the advantages of our method for assessing the capability of a nodulated legume to acquire nitrogen through both N(2) fixation and absorption and assimilation of NO(3) (-).

Journal Article↗
PubMed1977

Variability of nitrogen fixation in some isolates of Nostoc linckia.

Four clonal isolates of Nostoc linckia isolated from different localities were compared with respect to growth, nitrogen content (cellular and extracellular), and pigment composition. A considerable range of variation was observed among these isolates. This indicates the existence of genetically distinct clonal populations of the alga in natural habitats.

Carotenoids↗