Improved ε-poly-L-lysine production of an S-(2-aminoethyl)-L-cysteine resistant mutant of Streptomyces albulus

To improve the productivity of epsilon-poly-L-lysine (epsilon-PL) by Streptomyces albulus, S-(2-aminoethyl)-L-cysteine (AEC) plus glycine-resistant mutants were derived. Ninety-nine percent of the mutants were found to be high producers of epsilon-PL, and one of them (No. 11011A) showed a maximum productivity of 2.11 mg/ml in a test-tube culture, which was 10 times higher than that of the wild strain. In a 3-l mini jar fermenter, the mutant produced 20 mg/ml of epsilon-PL with an 8.9% yield against the consumed glucose in 120-h cultivation with glucose and ammonium sulfate feeding and continuous pH control: these values were 5.7 and ca. 4 times higher than those of the wild strain, respectively. The AEC + glycine-resistant mutants showed higher specific activities of aspatokinase, which is assumed to be a key enzyme for lysine biosynthesis of the strain, than the wild strain. There was little decrease in the specific activities of aspartokinase of the mutants when they were grown with lysine. In addition, the enzyme activity of the mutants was not inhibited by glycine as much as that of the wild strain. The improved epsilon-PL productivity of the mutants might be due to the increased specific activity of aspartokinase and the release from inhibition of aspartokinase by L-lysine and glycine.