Optimization of poly-ε-lysine production by Streptomyces noursei NRRL 5126

Poly-ε-lysine (ε-PL) is a non-toxic biopolymer with antimicrobial properties. The production of ε-PL by Streptomyces noursei NRRL 5126 shake-flask culture was optimized by identifying the most significant medium components which affect ε-PL production (glycerol, proteose peptone and ammonium sulphate) by Placket–Burman design and by application of an evolutionary operation (EVOP) to determine the optimal concentrations of these components. The ε-PL yield increased from 41.81 g/l in basal medium to 98.07 g/l in the EVOP-optimized medium containing 3% glycerol, 1% proteose peptone and 0.8% ammonium sulphate. Further improvements in media composition and culture conditions will be required to obtain yields comparable to those obtained with current commercial strains such as Streptomyces albulus.