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At least 433 records · Page 24Linked to original sources
PubMed1990

Enhanced Nodulation and Nitrogen Fixation by a Revertant of a Nodulation-Defective Bradyrhizobium japonicum Tryptophan Auxotroph.

In greenhouse studies, the symbiotic properties of a prototrophic revertant (TA11 NOD) of a nodulation defective tryptophan auxotroph of Bradyrhizobium japonicum were compared with those of the normally nodulating wild-type strain, B. japonicum I-110 ARS. Strain I-110 ARS was the parent of auxotrophic mutant TA11. Plants inoculated with TA11 NOD contained significantly more nitrogen per plant than did plants inoculated with wild-type bacteria (275.9 +/- 35 versus 184 +/- 18 mg). Also, plants that received the revertant were larger, averaging 8.4 +/- 0.9 g (dry weight) versus 6.4 +/- 0.6 g for those that received the wild-type bacterial strain. Additionally, plants that received the NOD strain had 56% more nodules and 41% more nodule mass than did control plants. With both inocula, average nodule size and amount of nitrogen fixed per gram of nodule were about the same. These data indicated that the improvement in nitrogen fixation observed with the TA11 NOD resulted from an increase in the overall nodule number. The physiological basis for this increase in nodulation is not known, but enhanced tryptophan catabolism does not appear to be involved.

Journal Article↗
PubMed1975

Nitrate reductase from bacteroides of Rhizobium japonicum: enzyme characteristics and possible interaction with nitrogen fixation.

The soluble nitrate reductase of Rhizobium japonicum bacteroids has been purified and its properties compared to those of aerobically grown cells. The enzymes from both sources are similar with molecular weights of about 70 000 suggesting no close relationship with the molybdo-protein component of nitrogenase. Nitrite, the product of nitrate reductase, strongly inhibited the nitrogenase activity from bacteroids, at concentrations less than 100 muM. Thus, an interference in the rate of nitrogen fixation is possible as a result of nitrate reductase activity. A study of the distribution of nitrate reductase in bacteroids indicates that a proportion of the total activity is membrane-bound but that this activity is similar to that in the soluble fraction. Purified nitrate reductase required reduced viologen dyes for activity. Neither NADPH or NADH or FAD could substitute as electron donors. Dithionite is a strong inhibitor and inactivated nitrate reductase from all sources examined. This inactivation is prevented by methyl viologen. Purified nitrate reductase from bacteroids and bacteria Rhizobium japonicum is practically unaffected by exposure to oxygen.

Chromatography, Gel↗
PubMed1985

Nitrogen Fixation Associated with the New Zealand Mangrove (Avicennia marina (Forsk.) Vierh. var. resinifera (Forst. f.) Bakh.).

Nitrogenase activity in mangrove forests at two locations in the North Island, New Zealand, was measured by acetylene reduction and N(2) uptake. Nitrogenase activity (C(2)H(2) reduction) in surface sediments 0 to 10 mm deep was highly correlated (r = 0.91, n = 17) with the dry weight of decomposing particulate organic matter in the sediment and was independent of light. The activity was not correlated with the dry weight of roots in the top 10 mm of sediment (r = -0.01, n = 13). Seasonal and sample variation in acetylene reduction rates ranged from 0.4 to 50.0 mumol of C(2)H(4) m h under air, and acetylene reduction was depressed in anaerobic atmospheres. Nitrogen fixation rates of decomposing leaves from the surface measured by N(2) uptake ranged from 5.1 to 7.8 nmol of N(2) g (dry weight) h, and the mean molar ratio of acetylene reduced to nitrogen fixed was 4.5:1. Anaerobic conditions depressed the nitrogenase activity in decomposing leaves, which was independent of light. Nitrogenase activity was also found to be associated with pneumatophores. This activity was light dependent and was probably attributable to one or more species of Calothrix present as an epiphyte. Rates of activity were generally between 100 and 500 nmol of C(2)H(4) pneumatophore h in summer, but values up to 1,500 nmol of C(2)H(4) pneumatophore h were obtained.

Journal Article↗
PubMed1976

Nitrogen fixation by hydrogen-utilizing bacteria.

Seventeen strains of nitrogen-fixing bacteria, isolated from different habitats on hydrogen and carbon dioxide as well as on other substrates, morphologically resembled each other. All strains, including Mycobacterium flavum 301, grew autotrophically with hydrogen. The isolate strain 6 was sensitive to oxygen when dependent on N2 as nitrogen source, a consequence of the sensitivity of its nitrogenase towards oxygen. At the same time, strain 6 was sensitive to hydrogen when growing autotrophically on N2 as nitrogen source, but hydrogen did not affect acetylene reduction by these cells.

Acetylene↗
PubMed1991

N coordination of FeMo cofactor requires His-195 of the MoFe protein alpha subunit and is essential for biological nitrogen fixation.

Electron spin echo envelope modulation (ESEEM) spectroscopy, a pulsed electron spin resonance technique, was used to analyze the N coordination of the iron-molybdenum (FeMo) cofactor contained within the nitrogenase MoFe protein. Comparison of spectra obtained from whole cells and purified MoFe protein established that the N coordination of the FeMo cofactor provided by the MoFe-protein polypeptide matrix can be unambiguously recognized in whole cells. ESEEM spectra of altered MoFe proteins, which were produced in certain mutant strains of Azotobacter vinelandii, showed that the N coordination to FeMo cofactor requires His-195 of the MoFe protein alpha subunit. Moreover, this requirement for His-195 was shown to be essential for biological nitrogen fixation.

Journal Article↗
PubMed1987

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

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.

Journal Article↗
PubMed1984

A Simple Technique of Studying Water Deficit Effects on Nitrogen Fixation in Nodules without Influencing the Whole Plant.

Cowpea (Vigna unguiculata L. Walp cv C-152) plants were grown in a system in which watering was withheld from the soil zone containing nodules, while the plants were able to maintain normal water status. The system was developed in a pot by making two soil zones, an upper and a lower separated by a gravel column between these two zones. Plants extended their roots into the lower layer of soil and were able to absorb water. The dry matter accumulation, photosynthesis rate, and leaf area development of the plant were not affected when the upper soil zone was dried, but the water potential of the nodules was lower than in the nodules in fully irrigated pots. Nitrogenase activity in the nodules obtained from plants stressed in the upper zone only was lower than in nodules obtained from fully irrigated plants. The present technique is helpful in distinguishing the direct water stress effects on nitrogen fixation compared to those mediated via photosynthate availability.

Journal Article↗
PubMed1989

Influence of Bradyrhizobium japonicum Location and Movement on Nodulation and Nitrogen Fixation in Soybeans.

The influence of seed and soil inoculation on bradyrhizobial migration, nodulation, and N(2) fixation was examined by using two Bradyrhizobium japonicum strains of contrasting effectiveness in N(2) fixation. Seed-inoculated strains formed fewer nodules on soybeans (mostly restricted to the tap and crown roots within 0 to 5 cm from the stem base) than did bradyrhizobia distributed throughout the soil or inoculated at specific depths. Nodulation was greater below the depths at which bradyrhizobial cells were located rather than above, even though watering was done from below to minimize passive bradyrhizobial migration with percolating water. The most profuse nodulation occurred within approximately 5 cm below the point of placement and was generally negligible below 10 cm. These and other results suggest that bradyrhizobial migration from the initial point of placement was very limited. Nevertheless, the more competitive strain, effective strain THA 7, migrated into soil to a greater extent than the ineffective strain THA 1 did. Nitrogen fixation resulting from the dual-strain inoculations differed depending on the method of inoculation. For example, the amount of N(2) fixed when both strains were slurried together onto the seed was about half that obtained from mixing the effective strain into the soil with the ineffective strain on the seed. The results indicate the importance of rhizobial distribution or movement into soil for nodulation, nodule distribution, strain competitiveness, and N(2) fixation in soil-grown legumes.

Journal Article↗
PubMed1991

Construction of an Acid-Tolerant Rhizobium leguminosarum Biovar Trifolii Strain with Enhanced Capacity for Nitrogen Fixation.

Strain ANU1173 is an acid-tolerant Rhizobium leguminosarum biovar trifolii strain that is able to nodulate subterranean clover plants growing in agar culture at pH 4.4 At pH 6.5, its symbiotic effectiveness in association with Trifolium subterraneum cv. Mt. Barker was 80% relative to that of strain ANU794, a Sm derivative of the commercial inoculant R. leguminosarum bv. trifolii TA1. Strain ANU1173 contained four indigenous megaplasmids, the smallest of these being the symbiotic (Sym) plasmid. The critical pH requirement for growth of strain ANU1173 in laboratory media was shown not to be associated with this plasmid. When the Sym plasmid of strain ANU1173(pSym-1173) was mobilized into a Nod strain of R. leguminosarum bv. viciae, the plasmid conferred to the transconjugant a level of symbiotic effectiveness in association with T. subterraneum that was similar to that observed with ANU1173. The symbiotic effectiveness of strain ANU1173 was improved by first curing pSym-1173 (generating strain ANU1184) and replacing it with another R. leguminosarum bv. trifolii Sym plasmid, pBR1AN. Subterranean clover plants inoculated with strain ANU1184 (pBR1AN) exhibited a 35 or 53% increase in acetylene reduction activity and a 20 or 17% increase in dry weight when grown at pH 6.5 and pH 4.4, respectively, compared with plants inoculated with strain ANU1173 and grown under the same pH conditions. It was further shown that pBR1AN was stably maintained in strain ANU1184 under free-living and symbiotic conditions. These results indicate that it is possible to construct an acid-tolerant strain of R. leguminosarum bv. trifolii with an enhanced capacity for nitrogen fixation.

Journal Article↗