Enhancement of ε-poly-l-lysine production coupled with precursor l-lysine feeding in glucose-glycerol co-fermentation by Streptomyces sp M-Z18

epsilon-Poly-l-lysine (epsilon-PL), one of the only two homo-poly amino acids known in nature, is used as a preservative. In this study, strategies of feeding precursor l-lysine into 5 L laboratory scale fermenters, including optimization of l-lysine concentration and time, was investigated to optimize the production of epsilon-PL by Streptomyces sp. M-Z18. The optimized strategy was then used in epsilon-PL fed-batch fermentation in which glucose and glycerol served as mixed carbon sources. In this way, a novel epsilon-PL production strategy involving precursor l-lysine coupled with glucose-glycerol co-fermentation was developed. Under optimal conditions, epsilon-PL production reached 37.6 g/l, which was 6.2 % greater than in a previous study in which glucose and glycerol co-fermentation was performed without added l-lysine (35.14 g/l). To the best of our knowledge, this is the first report of the enhancement of epsilon-PL production through l-lysine feeding to evaluate the use of fermenters. Meanwhile, the role of l-lysine in the promotion of epsilon-PL production, participating epsilon-PL synthesis as a whole, was first determined using the l-[U-C-13] lysine labeling method. It has been suggested that the bottleneck of epsilon-PL synthesis in Streptomyces sp. M-Z18 is in the biosynthesis of precursor l-lysine. The information obtained in the present work may facilitate strain improvement and efficient large-scale epsilon-PL production.