Hdbr-06 Lactococcus Lactis Nisin Producing Strain Breeding

Nisin is a small molecular peptide which is produced by lactococcus lactis. It can inhibit many gram positive bacteria as well as the growth and production of their spores. It is widely used in the field of food preservation as a natural food preservative for its high-efficient and nonpoisonous nature. The application field of Nisin has already expanded to paper making, food packing, agricultural feed, procreation and contraception, and the medical transplantation realms. The exploitation of Nisin will promote the development of green food industry and guarantee the food safety.In this research, the high yields Nisin-producing bacteria was breeded and screened while its cultivation and the fermentation medium was optimized. The highly Nisin-producing mutant strain DU101 was obtained from HDBR-06 by series of mutagenetic treatment, i.e. UV, NTG, DES, and DES& UV. The activity of Nisin of DU101 was 1389IU/mL, which was 3.12 times more than the initial strain HDBR-06. Subculture test indicted that the hereditary character of DU101 was stable.After single factor experiments based on MRS fermentation medium, corn steep liquor and glucose were determined as carbon and nitrogen sources respectively. Then the fermentation medium of the mutant strain DU101 was optimized. Firstly, Plackett-Burman design was used to evaluate the influences of all related factors in fermentation medium.The results showed that glucose and NaAc were the main affecting factors while the other additives had no significant effects on titre of Nisin. Then the optimum fermentation medium was determined according to CCD (Central composit Design) and Response Surface Analysis with SAS software. The optimal fermentation medium for Nisin production was: corn steep liquor 5g/L,glucose 6.57g/L,citric acid ammonium 3g/L,K2HPO4 2g/L,NaAc 7.11g/L,MgSO₄·7H₂O 0.2g/L,MnSO₄·H₂O 0.05g/L,Tween 80 2mL/L。Under this fermentation medium condition, the activity of Nisin of DU101 was 1564IU/mL, which is 3.51 times more than the initial strain HDBR-06.