Characterization of plant growth promoting rhizobacterial strain Bacillus cereus with special reference to exopolysaccharide production

Abstract

Exo-polysaccharides (EPS) possess unique water holding and cementing properties that help in soil aggregation. EPS also increase nutrient uptake in plants, increase water flow across the roots, reduce saline stress by up taking Na+ from soil and increases plant resistance to drought stress. All these factors lead to investigate for eco-friendly and economically reasonable sources of exo-polysaccharides. The exo-polysaccharides secreted by bacteria might play potential role in improvement of agricultural productivity. In the present study, seven bacterial isolates from rice rhizosphere were characterized for their plant growth promoting traits. The isolate NP6 showed most promising results with indole-3-acetic acid production, phosphate solubilization, hydrogen cyanide production, ammonia production, nitrogen fixation along with significant amount of exo-polysaccharides production. The strain was identified as Bacillus cereus by 16S rDNA sequencing method. The co-inoculation of NP6 with pathogenic fungal strain Alternaria alternata showed 86% inhibition of the mycelial growth. For NP6, fructose and peptone were proved to be most optimum carbon and nitrogen sources respectively for exo-polysaccharide production. At a C/N ratio of 20, highest exo-polysaccharides production was observed. In presence of salinity stress NP6 is also able to secrete considerable amount of EPS. All these properties of NP6 make it a candidate to be utilized in large scale exo-polysaccharides production as well as bio-inoculant for improvement of soil condition.