Abstract:[Objective] With Streptomyces noursei GX6 (S. noursei GX6) as the starting strain, strain breeding was carried out to increase the yield of ε-poly-lysine (ε-PL) and solve the problem of sporulation ability degradation of the mutant strain. Then, pH regulation of fermentation was employed to further increase the ε-PL yield of the mutant strain.[Method] Ion implantation mutagenesis combined with multi-antibiotic resistance screening was carried out for S. noursei GX6, and high-yield mutant strains of ε-PL were screened. Then, the components and their mass concentrations of various culture media were optimized for cultivating the high-yield strain, and the sporulation was observed. Finally, fermentation experiments with constant pH and pH shocks were carried out in a 5 L fermenters.[Result] The high-yield mutant strain S. noursei T9 obtained through breeding had a ε-PL yield of 2.97 g/L in shake flasks. The use of the MGY medium (containing soybean powder, mannitol, glucose, yeast extract, and CaCO3) effectively restored the sporulation ability of S. noursei T9. Moreover, this strain maintained genetic stability after 10 passages. During the fed-batch fermentation with constant pH 4.0 in the fermenter, the ε-PL yield of S. noursei T9 reached 56.8 g/L, which was 20.3% higher than that (47.2 g/L) of S. noursei GX6. When the pH shock strategy was further adopted, a single shock increased the ε-PL yield to 62.1 g/L, with an increase of 9.3%, while two pH shocks further increased the ε-PL yield to 69.5 g/L, with the production efficiency reaching 0.006 3 g/(g·h).[Conclusion] This study provides practical strategies for addressing the insufficient sporulation capacity and increasing the ε-PL yield of S. noursei in industrial production.
