Low Energy N + Implantation Nisin A Preliminary Study Of Bacteria Mutation Breeding

The nisin producer Lactococcus lactis AS 1.2030 was mutated by low energy N⁺ ions beam implanting and UV for screening high yield strain in this study. The strain J7, one of mutants was showed preference to produce nisin. The nisin activity of J7 was 1655.99IU/ml and was more 71.01% than that of AS1.2030. The result of genetic stability experiment of 5 generations showed that strain J7 produced nisin activity from 94% to 102%. The strain J7 was cultured with 6 culture medium and the result showed that LTB was the optimum one. The orthogonality experiment was used to optimize LTB cultural conditions, and the result showed that the optimal culture conditions were glucose 0.5%, NaCl 0.7%, Na₂HPO₄·12H₂O 0.2%, yeast cream 1.0%, beef cream 1.5%, tryptone 1.5%, pH 6.4. The nisin activity of strain J7 was 1732.45IU/ml under the optimal LTB culture condition.Meanwhile, the method of agar diffusion bioassay for nisin was optimized. The results showed that when agar concentration was 0.75%, the addition of tween20 was 0.5%, the culture temperature was 300℃, the accuracy and sensitivity of agar bioassay for nisin could be improved. And the pre-diffusion at 4℃ could improve the diffusion of nisin in agar.