Optimized Production of Poly(γ-Glutamic acid) By Bacillus sp. FBL-2 through Response Surface Methodology Using Central Composite Design

In the present study, the optimization of poly(gamma-glutamic acid) (gamma-PGA) production by Bacillus sp. FBL-2 was studied using a statistical approach. One-factor-at-a-time method was used to investigate the effect of carbon sources and nitrogen sources on gamma-PGA production and was utilized to select the most significant nutrients affecting the yield of gamma-PGA. After identifying effective nutrients, response surface methodology with central composite design (CCD) was used to obtain a mathematical model to identify the optimum concentrations of the key nutrients (sucrose, L-glutamic acid, yeast extract, and citric acid) for improvement of gamma-PGA production. The optimum amount of significant medium components appeared to be sucrose 51.73 g/l, L-glutamic acid 105.30 g/l, yeast extract 13.25 g/l, and citric acid 10.04 g/l. The optimized medium was validated experimentally, and gamma-PGA production increased significantly from 3.59 g/l (0.33 g/l/h) to 44.04 g/l (3.67 g/l/h) when strain FBL-2 was cultivated under the optimal medium developed by the statistical approach, as compared to non-optimized medium.