Exploration of rice bran, an agro-industry residue, for the production of intra- and extra-cellular polymers by Sinorhizobium meliloti MTCC 100

The present work was focused on simultaneous production of certain intra- and extra-cellular polymers by fast growing Sinorhizobium meliloti MTCC 100 using rice bran, a low cost agro-industry residue, in hydrolyzed form to enhance product yields. The culture produced 3.63 g/L of biomass, 1.75 g/L of intra-cellular polymer (polyhydroxyalkanoate, PHA) and 1.2 g/L of extra-cellular polymer (exopolysaccharide, EPS) in control, polymer production (PP) medium. Supplementation of 20% rice bran hydrolysate (RBH) to PP medium at 0 h resulted in increased production of biomass, PHA and EPS (5.92, 2.71 and 2.01 g/L, respectively). Addition of RBH at after 24 h of fermentation increased the amount of EPS by 5 folds after 72 h at 30 °C. An initial pH of 7.0 and fermentation temperature of 30 °C were found to be optimum for the production of biomass as well as both the biopolymers. The biomass, PHA and EPS contents increased with the increase in fermentation period from 24 h to 72 h, with a maximum biomass of 7.45 g/L and PHA of 3.60 g/L. With further incubation to 96 h EPS production increased to 11.8 g/L. Gas chromatography and Fourier transform infra red spectroscopy of the PHA indicated it to be a copolymer of polyhydroxybutyrate and polyhydroxyvalerate.