Isolation and characterization of Sinorhizobium and Ensifer species isolated from root nodules of Vigna trilobata cultivars

A total of eight rhizobacterial strains were isolated from the root nodules of Vigna trilobata plants raised in soils of different districts of Andhra Pradesh, India. Morphologically all the strains were rod shaped gram negative and mucus producing. All these strains were positive for biochemical tests such as ammonia production, catalase test, oxidase test, nitrate reduction test, and urease test. These strains gave negative results for Ketolactose test, growth on glucose peptone agar medium and Hoffer’s Alkaline medium. For amylase activity, three strains Sinorhizobium sp. MRR 101, Sinorhizobium sp. MRR 109 and E.xinjiangense MRR 110 showed negative results and rest of the strains showed positive results. For citrate utilization test except Ensifer sp. MRR 125 all isolates showed the positive results. Good colony growth was recorded at 0.1% NaCl with pH range of 7-8 and temperatures between 30⁰C - 35⁰C for all the strains studied. Indole acetic acid and EPS production was common for all the strains with IAA production in range from 8.5-70µg/ml, and EPS production from 379-892 mg/ml. Two out of eight strains i.e. Sinorhizobium sp. MRR 101 (250 µg/ml) and S.kostiense MRR 104 (510 µg/ml) exhibited phosphate solubilisation ability. Only one strain E. xinjiangense MRR 110 showed the chitinase activity (0.30 U/ml) on colloidal chitin agar medium. And three strains viz., S. kostiense MRR104, E.xinjiangense MRR 110, S. terange MRR 121 were HCN producers. None showed siderophore production. Among the eight strains, Sinorhizobium sp.MRR 101, S.kostiense MRR 104, and E.xinjiangense MRR 110 were proved to be better as plant growth promoting rhizobateria.