[Improving heat and pH stability of nisin by site-directed mutagenesis].

Objective: The aim of this study was to optimize the property of nisin through altering its specific amino acid by site-directed mutagenesis method.

Methods: On the basis of M21K nisinZ, a former reported nisinZ mutant that exhibited antimicrobial activity against Gram-negative bacteria, the 29th amino acid of it was mutated from serine to lysine. The mutant M21K/S29K nisZ gene was cloned into vector pMG36e and the recombinant plasmid was introduced into Lacotococcus lactis NZ9800. The resulting M21K/S29K nisinZ was then isolated and purified, and its antibacterial activity, antibacterial spectrum and stability were analyzed and compared to those of M21K nisinZ and nisinZ.

Results: Compared with wild-type nisinZ and M21K nisinZ, the M21K/S29K nisinZ displayed reduced antimicrobial activity, but showed significantly increased stabilities to heat and pH stress. Moreover, M21K/S29K nisinZ also exhibited antimicrobial activity against Gram-negative bacteria as M21K nisinZ did.

Conclusion: By changing the 29th amino acid of nisin, we can optimize the property of nisin, especially its stability to heat and pH stress.