GENES RESPONSIBLE FOR NISIN SYNTHESIS, REGULATION AND IMMUNITY FORM AREGULON OF 2 OPERONS AND ARE INDUCED BY NISIN IN LACTOCOCCUS-LACTIS N8

Nisin is a small post-translationally modified lanthionine-containing peptide (lantibiotic) produced by certain Lactococcus lactis strains w hich has a high antimicrobial activity against several pathogenic Gram -positive bacteria. Northern blots and RT/PCR analyses of the nisin-pr oducing strain N8 revealed that the nisZBTCIPRKFEG gene cluster, respo nsible for nisin biosynthesis, immunity and regulation, consists of tw o operons, nisZBTCIPRK and nisFEC. The promoter of the nisFEC operon w as mapped. The -35 to -1 region upstream of the transcription start of the nisFEC promoter showed 73% identity with the corresponding region upstream of the nisA and nisZ gene. In contrast to earlier reports, n isin was found to be secreted during the early stages of growth as wel l 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-expone ntial growth, when the ph in the medium fell below 5.5. In nisZB antis ense and nisT deletion mutant strains constructed in this study the tr anscription of the nisin operons, nisin production and immunity were l ost. Provision of external nisin restored the transcription of both op erons 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 i n the level of immunity. Induction using higher concentrations of nisi n yielded a higher level of immunity. These results showed that the ni sin promoters are under positive control in an autoregulatory manner a nd that antimicrobial peptides can also function as signal molecules.