Medium optimization for the production of exopolysaccharide by Bacillus subtilis using synthetic sources and agro wastes

Exopolysaccharides (EPSs) play an extensive role as biopolymers in the environment by replacing synthetic polymers as they are degradable, nontoxic, and produced by microorganisms. An attempt was made to optimize a medium, by the one-factor-at-a-time method, for an enhanced production of EPS from a soil isolate, Bacillus subtilis. The study was carried out by experimenting on various nutrients at different concentrations. EPS was precipitated using ethanol, the total carbohydrate content was determined by phenol sulfuric acid method, and functional groups were detected by Fourier transform infrared (FTIR) spectrophotometry. The finalized medium contained sucrose (20 g/L), yeast extract (5 g/L), NaCl (7 g/L), CaCl2 (0.5 g/L), L-asparagine (0.05 g/L), and ascorbic acid (0.05 g/L). The carbon source was replaced with certain agro substrates, cane molasses, and rice bran. Cane molasses at a concentration of 2% gave the highest yield of 4.86 g BPS/L as compared to a medium with sucrose (2.98 g EPS/L). The effect of UV radiations on growth and synthesis was negative, decreasing the growth rate and quantity of BPS produced. Different solvents were checked for their efficiency on precipitating BPS; those other than ethanol, diethyl ether, and methanol were not able to sediment the polymer. FTIR analysis of the extracted product revealed that the polymer was made up of units of sucrose. Thus, the present study showed that the agro wastes could be an alternative for synthetic substrates, providing a way for an economical production of EPS.