Nitrogenase activity (C2H2 reduction) was demonstrated in seedlings of wheat roots bearing para-nodules induced by 2,4-dichlorophenoxyacetic acid (2,4-D) and inoculated with Azospirillum brasilense. Increased nitrogenase activity was observed in inoculated para-nodulated seedlings as compared to inoculated roots not treated by 2,4-D under the conditions of assay used. 2,4-D had no stimulating e...

The root-to-root travel of the beneficial bacterium Azospirillum brasilense on wheat and soybean roots in agar, sand, and light-textured soil was monitored. We used a motile wild-type (Mot) strain and a motility-deficient (Mot) strain which was derived from the wild-type strain. The colonization levels of inoculated roots were similar for the two strains. Mot cells moved from inoculated roots (...

The occurrence in Azospirillum brasilense of genes that code for exopolysaccharide (EPS) synthesis was investigated through complementation studies of Rhizobium meliloti Exo- mutants. These mutants are deficient in the synthesis of the major acidic EPS of Rhizobium species and form empty, non-nitrogen-fixing root nodules on alfalfa (J. A. Leigh, E. R. Signer, and G. C. Walker, Proc. Natl. Acad....

Nitrogen-fixing, plant-growth promoting bacteria are arguably the biotechnological tool of highest potential to improve agricultural productivity in short term. Nitrogen fixation and phytohormone production by these bacteria have been considered the most important factors for plant growth promotion. However, the underlying mechanisms responsible for productivity increases by associative bacteri...

Azospirillum lipoferum and Pyricularia oryzae laccases were compared, using several substrates and inhibitors. Sixteen phenolic or nonphenolic compounds were found to be substrates of both fungal and bacterial laccases. In the presence of different phenol oxidase inhibitors, P. oryzae and A. lipoferum laccase activities had similar properties.

The activity of a truncated form of Herbaspirillum seropedicae NifA in different genetic backgrounds showed that its regulatory domain is involved in nitrogen control but not in O2 sensitivity or Fe dependence. The model for nitrogen control involving PII could thus apply to the proteobacteria at large. NifA may have a role in controlling ADP-ribosylation of nitrogenase in Azospirillum brasilense.

Seasonal variations of population dynamics of free living nitrogen fixing bacteria, Azospirillum in relation to chemical parameters in Manakkudi mangrove ecosystem was assessed in root and rhizosphere soil samples of mangroves and mangrove associated plants. In rhizosphere soil and root samples, the counts of Azospirillum were recorded maximum in Acrostichum aureum as 8.63 +/- 0.92 x 10(4) and ...

Some biophysical features of the diazotroph Azospirillum brasilense Sp7-S were studied. It maintained a stable but relatively low membrane potential (v8) of about 385 mV in conditions typical of aerated soil solutions. Internal pH was also well regulated at about 7.4 from pH 6^8. The calculated proton motive force was maximal at 3220 mV in pH 5.0 medium, decreasing to zero at pH 8.8. This proto...

The N2 fixing bacteria Klebsiella pneumoniae, Azospirillum brasilense, Rhodopseudomonas sphaeroides and Rhodospirillum rubrum, but not Azotobacter vinelandii accumulate the glutamine analogue methionine sulfoximine in the cell. In the accumulating cells methionine sulfoximine inhibits ammonium transport. Accumulation and inhibition are prevented by glutamine.

Sequencing the glnA genes of two chemically induced Azospirillum brasilense glutamine synthetase mutants revealed an Arg-->Cys mutation, corresponding to the glutamate binding site, in one mutant and an Asp-->Asn mutation, corresponding to the ammonium binding site, in the second mutant. The phenotypic changes in these mutants are discussed in relation to their genotypes.