Enhancement of ε-poly-lysine production in ε-poly-lysine-tolerant Streptomyces sp. by genome shuffling.

ε-Poly-L-lysine (ε-PL) has been widely used as food additive. However, the self-inhibition of ε-PL on cell growth limits the accumulation of ε-PL in the wild-type strain. Here, we screened ε-PL-tolerant strain of Streptomyces sp. with higher ε-PL productivity by genome shuffling and studied the mechanism for the improvement. The initial mutant library was constructed by diethyl sulfate mutagenesis. After four rounds of protoplast fusion, a shuffled strain F4-22 with 3.11 g/L ε-PL productivity in shake flask, 1.81-fold in comparison with that of parent strain, was obtained. The higher aspartokinase activity was induced in F4-22 whereas no obvious changes have been found in ε-PL synthetic and degrading enzymes which indicated that the upstream reregulation of the precursor lysine synthesis rather than lysine polymerization or ε-PL degradation in shuffled strain accounted for the higher productivity. The activities of key enzymes in the central metabolic pathway were also enhanced in F4-22 which resulted in increased vigor of the strain and in delayed strain lysis during fermentation. These improved properties of shuffled strain led to the success of combining general two-stage fermentation into one-stage one in 5-L bioreactor with 32.7 % more ε-PL production than that of parent strain. The strategy used in this study provided a novel strain breeding approach of producers which suffered from ε-PL-like self-inhibition of the metabolites.