Abstract: The culture conditions for poly γ-glutamic acid production by Bacillus subtilis ZJS18 were optimized by response surface methodology (RSM). Three factors that had a significant influence on the yield of poly γ-glutamic acid, namely sucrose, yeast powder and sodium glutamate, were screened out by the Plackett-Burman design. The levels of the three medium components were further optimized to be 64.40, 7.10 and 57.96 g/L, respectively using Box-Behnken design with RSM. The optimal culture conditions for the production of poly γ-glutamic acid were as follows: sucrose 64.40 g/L, yeast powder 7.10 g/L, sodium glutamate 57.96 g/L, NaCl 30 g/L, KH2PO4 2 g/L, MgSO4 0.3 g/L, initial pH 7.5, inoculum size 5%, medium volume 40 mL/250 mL, temperature 37 ℃, shaking speed 200 r/min, and fermentation time 36 h. Under the above conditions, the yield of poly γ-glutamic acid was up to 13.20 g/L, which was increased by 2.88 folds as compared to that under the original conditions.

Key words: Bacillus subtilis, poly γ-glutamic acid, culture conditions, response surface methodology, optimization