Cloning of two bacteriocin genes from a lactococcal bacteriocin plasmid.

Lactococcus lactis subsp. cremoris 9B4 plasmid p9B4-6 (60 kilobases [kb]), which specifies bacteriocin production and immunity, was analyzed with restriction endonucleases, and fragments of this plasmid were cloned into shuttle vectors based on the broad-host-range plasmid pWVO1. Two regions on p9B4-6 were identified which specify inhibitory activity on L. lactis indicator strains: one that could be confined to a 1.8-kb ScaI-ClaI fragment with low antagonistic activity and a 15-kb XbaI-SalI fragment specifying high antagonistic activity. The inhibitory substances produced by these two clones were sensitive to proteolysis. A 4-kb HindIII fragment derived from the 15-kb fragment strongly hybridized with the 1.8-kb fragment. The antagonistic activity specified by the 4-kb fragment was somewhat reduced as compared with that of the 15-kb fragment. A 1.3-kb ScaI-HindIII subfragment of the 4-kb fragment contained both the immunity and bacteriocin genes. Inhibition studies showed that the two bacteriocins had different specificities.