Estimation and optimization of exopolysaccharide production from rice rhizospheric soil and its interaction with soil carbon pools

Exopolysaccharides (EPS) the high molecular weight microbial substances play an important role in enhancing soil aggregation as well as maintaining water holding capacity around the rhizosphere. Therefore, looking into the fact that rice is one of the important food crops for most of the people of the world and the ability of EPS to increase the uptake of nutrients by plants and protect from drought stress. The present investigation was carried out to study the EPS production by bacteria isolated from rice cultivar Naveen with four treatments viz., aerobic (−5 kPa), saturation (0 kPa), submerged (2 cm standing water) and control (without any water treatment) and their interaction with soil labile carbon pools. Soil (0–15 cm depth) was collected from panicle initiation stage of the crop growth to isolate EPS producing bacteria. Different parameters like microbial biomass carbon (MBC), readily mineralizable carbon (RMC) and organic carbon (OC) alongwith total and colloidal EPS were estimated. The total and colloidal EPS increased 26.0% and 9.0% among the treatments over saturation. The MBC, RMC and OC were found to increase 30.0%, 19.0% and 4.0% among the treatment over saturation. These findings indicated a positive correlation between carbon pools and total and colloidal EPS production. Similarly, in this study, 22 EPS producing bacteria were isolated from the rice rhizospheric region and amongst 4 isolates were found to tolerate maximum level of water stress (−0.73 MPa). Further, optimization studies indicated that all these 4 bacterial isolates produced EPS at 37 °C, 80 mM salt concentration and pH value 7.5 within 3 days of incubation. Further, among different carbon sources, sucrose followed by glucose was found to be best for production of EPS. Further work is going on to evaluate the efficacy of these potential EPS producing bacterial isolates under field conditions.