Screening of High-Yield Nisin-Producing Lactococcus lactis Mutants Using Adaptive Mutation Methods

Abstract

Lactococcus lactis subspecies lactis ATCC 11454 is a natural nisin A-producing strain. It was used as the parent strain for adaptive mutations in this study to screen for high-yield nisin-producing mutants. Through a series of classical mutations with physical and chemical mutagenic agents, including ultraviolet, LiCl, and diethylsulfate (DES), followed by adaptive mutation in a nutrient medium containing high concentrations of nisin, two high-yield nisin-producing mutant isolates 3807 and 3823 were obtained. In shake flask fermentation experiments, 3807 and 3823 strains produced nisin at 2,160 IU/mL and 2,140 IU/mL, respectively, in the fermented broth—more than 3 times higher than the parent strain ATCC 11454. These mutants were relatively stable over sub-culturing for 3 passages. In a 10-L fermentor, the mutant 3807 produced an average of 11,870 IU/mL of nisin. At 700-L fermentation scale, the average yield was 10,350 IU/mL. When it was scaled up to 50-ton fermentation, it yielded an average of 9,960 IU/mL of nisin A in the fermented medium.