Nisin is a small post-translationally modified lanthionine-containing peptide (lantibiotic) produced by certain strains which has a high antimicrobial activity against several pathogenic Gram-positive bacteria. Northern blots and RT/PCR analyses of the nisin-producing strain N8 revealed that the gene cluster, responsible for nisin biosynthesis, immunity and regulation, consists of two operons, and The promoter of the operon was mapped. The −35 to −1 region upstream of the transcription start of the promoter showed 73% identity with the corresponding region upstream of the and gene. In contrast to earlier reports, nisin was found to be secreted during the early stages of growth as well as later in the growth cycle. The secreted nisin was adsorbed on the surface of the cells and was released to the medium during mid-exponential growth, when the pH in the medium fell below 5.5. In antisense and deletion mutant strains constructed in this study the transcription of the nisin operons, nisin production and immunity were lost. Provision of external nisin restored the transcription of both operons in the mutant strains, showing that the operons are coordinately regulated by mature nisin. Nisin induction of the mutant strains also resulted in an increased amount of the Nisl protein and an increase in the level of immunity. Induction using higher concentrations of nisin yielded a higher level of immunity. These results showed that the nisin promoters are under positive control in an autoregulatory manner and that antimicrobial peptides can also function as signal molecules.


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