Medium Optimization for ε-Poly-L-Lysine Production by Streptomyces diastatochromogenes Using Response Surface Methodology.

Poly-epsilon-L-lysine is a natural homo-polyamide of L-lysine with excellent antimicrobial properties, which can be used as a novel preservative and has a wide range of applications. In this paper, the fermentation medium for epsilon-PL production by Streptomyces diastatochromogenes 6#-7 was optimized by Response Surface Methodology. The results of Plackett-Burman design showed that glucose, yeast extract and (NH4)(2)SO4 were the major influencing factors in epsilon-PL production of S. diastatochromogenes 6#-7. The optimal concentrations of glucose, yeast extract and (NH4)(2)SO4 were determined to be 60, 7.5 and 7.5 g l(-1) according to Box-Behnken experiment and regression analysis, respectively. Under the optimized conditions, the epsilon-PL yield in shake-flask fermentation was 0.948 +/- 0.030 g l(-1), which was in good agreement with the predicted value of 0.970 g l(-1). The yield was improved by 43.1% from that with the initial medium. In 5 l jar-fermenter the epsilon-PL yield reached 25.5 g l(-1), which was increased by 56.4% from the original medium. In addition, the fermentation time was reduced from 174 to 120 h.