Genetic determinants for the biosynthesis of nisin, a bacteriocin produced by Lactococcus lactis.

In the past, the genetic determinants for nisin biosynthesis were thought to be plasmid-located. However, it has been shown that production of nisin, immunity to nisin, and other properties such as the fermentation of sucrose, are encoded on 70 kb conjugative transposons that are chromosomally located. The extrachromosomal location of the nisin genes has not been substantiated by experiments that unequivocally show plasmid transfer. Two natural variants of nisin have been identified, nisin A and nisin Z, encoded by the genes nisA and nisZ, respectively. Both genes have been cloned and sequenced and differ only in a single base pair. Approximately 12 kb downstream from the structural gene has been cloned and sequenced, and a further 10 genes involved in the biosynthesis of nisin have been identified. The nisB and nisC gene products are involved in nisin maduration, the nisT in its secretion and the nisP in its processing. The nisR and nisK gene products have a regulatory role and the nisI, nisF, nisE and nisG are involved in immunity to nisin. All these genes display significant homology to the corresponding genes of the related lantibiotics subtilin and epidermin.