In the present study, the optimization of poly(γ-glutamic acid) (γ-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 γ-PGA production and was utilized to select the most significant nutrients affecting the yield of γ-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 γ-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 γ-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.
Keywords: Bacillus sp. FBL-2; L-glutamic acid; Poly(γ-glutamic acid); optimization; response surface methodology.