CHARACTERIZATION OF THE LACTICIN-481 OPERON - THE LACTOCOCCUS-LACTIS GENES LCTF, LCTE, AND LCTG ENCODE A PUTATIVE ABC TRANSPORTER INVOLVED IN BACTERIOCIN IMMUNITY

The lantibiotic lacticin 481 is a bacteriocin produced by Lactococcus lactis strains. The genetic determinants of lacticin 481 production ar e organized as an operon encoded by a 70-kb plasmid. We previously rep orted the first three genes of this operon, lctA, lctM, and lctT, whic h are involved in the bacteriocin biosynthesis and export (A. Rince, A . Dufour, S. Le Pogam, D. Thuault, C. M. Bourgeois, and J.-P. Le Penne c, Appl. Environ. Microbiol. 60:1652-1657, 1994). The operon contains three additional open reading frames: lctF, lctF, and lctG. The hydrop hobicity profiles and sequence similarities strongly suggest that the three gene products associate to form an ABC transporter. When the thr ee genes were coexpressed into a lacticin 481-sensitive L. lactis stra in, the strain became resistant to the bacteriocin. This protection co uld not be obtained when any of the three genes was deleted, confirmin g that lctF, lctE, and lctG are all necessary to provide immunity to l acticin 481. The quantification of the levels of immunity showed that lctF, lctE, and lctC could account for at least 6% and up to 100% of t he immunity of the wild-type lacticin 481 producer strain, depending o n the gene expression regulation. The lacticin 481 biosynthesis and im munity systems are discussed and compared to other lantibiotic systems .