Statistical optimization of fermentation conditions for the improved production of poly-β-hydroxybutyrate fromBacillus subtilis

Poly-β-hydroxybutyrate (PHB) has been an effective biodegradable plastic obtained by microbial fermentation. Batch fermentation of Bacillus subtilis features an attractive system for the production of PHB. Identification of appropriate media components and cultivation conditions are extremely important for the optimal production of biomass and/or PHB production. Statistical media design was utilized for the optimization of different fermentation variables (glucose, peptone, sodium chloride, K2HPO4, KH2PO4, ammonium sulfate, ammonium chloride, sodium sulfate, temperature, inoculum size, and pH). The optimized media predicted the optimal dry cell weight of 7.54 g L−1 and PHB production of 77.2 mg L−1 at 1 g L−1 of peptone, 1.46 g L−1 sodium sulfate, and pH 6.8 in 24 h. Glucose utilization, batch growth, and PHB production kinetics of B. subtilis were determined experimentally. The effect of substrate inhibition on specific growth rate was also determined experimentally for B. subtilis. The values of kinetic and substrate inhibition parameters obtained from this study shall be utilized to develop a mathematical model for PHB production for further improving the production of PHB.