Symbiotic effectiveness of bacteriocin producing and non-producing strains of Rhizobium in green gram (Vigna radiata).

Rhizobium strains nodulating green gram [Vigna radiata (L.) Wilczek] were found to produce bacteriocin on modified Bergersen's medium and inhibited the growth of homologous Rhizobium strains. Four bacteriocin producing and four bacteriocin non-producing strains were compared for their effect on nodulation, in planta nitrogenase activity and plant dry weight of green gram. The bacteriocin producers formed more nodules in comparison to non-bacteriocin producers. However, the symbiotic effectiveness of bacteriocin producers was less in terms of plant dry weight in comparison to non-bacteriocin producers.

Analogue-resistant mutants of Azotobacter chroococcum derepressed for nitrogenase activity and early ammonia excretion having potential as inoculants for cereal crops.

Spontaneous mutants resistant to methionine sulfoximine (Msx), methyl alanine (Mal) and methyl ammonium chloride (Mac) were derived from A. chroococcum strain A103. Msx and Mal-resistant mutants expressed 1.73 to 10.98% of the fully derepressed nitrogenase activity when grown in Burk's medium containing ammonium acetate. Mac-resistant mutants did not express nitrogenase activity in ammonium acetate supplemented medium. The mutants excreted ammonia even after 2 days of growth and some mutants excreted more ammonia as compared to the parent. Selected mutants were inoculated on wheat (Triticum aestivum) and barley (Hordeum vulgare) under field conditions. Majority of the derepressed mutants increased grain yield of wheat and barley varying from 1.2 to 33.3%. However, host-dependent effects on grain yield were observed with different mutants. Two mutants, Mal 27 and Mac 19 showed significant increase in grain yields of both the crops. The results suggest that metabolic analogue-resistant mutants of Azotobacter have potential for use as a biofertilizer for cereal crops.

Rhizobium strains expressing uptake hydrogenase in different host species of cowpea miscellany.

Uptake hydrogenase activity in nodules of green gram (Vigna radiata (L.) (Wilczek)), black gram (Vigna mungo (L.) (Hepper)), cowpea (Vigna unguiculata (L.) and cluster bean (Cyamopsis tetragonoloba (L.) (Taub.)), formed with two Hup+ (S24 and CT2014) and one Hup– (M11) Rhizobium strains, was determined at different levels of external H2 in air atmosphere. Nodules of all the 4 host species formed by inoculation with strains S24 and CT2014, showed H2 uptake but not those formed with strain M11. H2 uptake rates were higher in 1 and 2% H2 in air atmosphere (v/v) than at 5 or 10% levels in all the host species. Variations in the relative rates of H2 uptake were observed both, due to host species as well as due to Rhizobium strains. However, no host dependent complete repression of the expression of H2 uptake activity was observed in nodules of any of the host species formed with Hup+ strains.