[Enhanced nisin production by overexpression of nisin immunity gene nisI in the nisin-producing strain].

OBJECTIVE: Our aim was to enhance nisin production by overexpression of nisin immunity gene nisI in nisin-producing strains. METHODS: Nisin immunity gene nisI with a strong promoter P59 was cloned into vector pHJ201 and introduced into Lacotococcus lactis NZ9800, resulting in a recombinant strain L. lactis NZ9800/pHMI. Then the differences between the recombinant strain and the control strain L. lactis NZ9800/pHJ201 were analyzed in several aspects, including their growth curves, nisin resistance level and antibacterial activity against indicator strain Microccus flavus NCIB 8166. RESULTS: The overexpression of nisI had no significant difference in growth rate between recombinant strain and contrast strain. However, it promoted recombinant strain tolerance 25% higer nisin resistance level and stronger antibacterial activity against M. flavus NCIB 8166, which was increased by 32% and 25% when fermented for 6 and 8 hours, respectively. CONCLUSION: These results indicated that overexpression of nisI gene in the nisin producing strain can effectively enhance nisin resistence level and thus improve nisin production.