Screening and optimization of exopolysaccharide producing bacteria from rhizospheric region of direct seeded rice

Abstract

Exopolysaccharide (EPS) are high molecular weight substances mainly comprise of polysaccharides but also contains non-sugar components like protein, nucleic acid and lipids which mainly originated from microbial origin. With the rising awareness of microbial EPS in various fields, rice rhizospheric microorganisms received broad attention and play a crucial role in protecting crops during the stress condition. The present study was to obtain exopolysaccharide producing bacteria from direct seeded rice. Soil samples were collected from rice rhizospheric region (0-15cm depth). Thirty-seven organisms were isolated and identified by morphological, biochemical and microscopic analysis. Out of thirty-seven isolates eighteen isolates produced mucoid substances and having Gram -ve in nature. After screening with Polyethylene glycol (PEG-6000), six isolates tolerate maximum level of stress (-0.73MPa). The production of six isolates were ranged from 3.4 to 5.5g/l. The six potential isolates were optimized with temperature, pH, incubation period, salt concentration and carbon source. We found that, 37 0C and 7.5 pH were optimum for EPS production. The production rate was decreased with increasing pH and salt concentration. Sucrose was the suitable carbon source for production of EPS. The finding of the study implies the isolates have potential to produce EPS from rice rhizospheric region. Further study should aim to molecular identification EPS producing bacteria linking with drought tolerance and water use efficiency under direct seeded rice.