Biological and molecular characterization of a two-peptide lantibiotic produced by Lactococcus lactis IFPL105

The lactic acid bacterium Lactococcus lactis IFPL105 secretes a broad spect rum bacteriocin produced from the 46 kb plasmid pBAC105. The bacteriocin wa s purified to homogeneity by ionic and hydrophobic exchange and reverse-pha se chromatography. Bacteriocin activity required the complementary action o f two distinct peptides (alpha and beta) with average molecular masses of 3 322 and 2848 Da, respectively. The genes encoding the two peptides were clo ned and sequenced and were found to be identical to the ltnAB genes from pl asmid pMRC01 of L. lactis DPC3147. LtnA and LtnB contain putative leader pe ptide sequences similar to the known 'double glycine' type. The predicted a mino acid sequence of mature LtnA and LtnB differed from the amino acid con tent determined for the purified alpha and beta peptides in the residues se rine, threonine, cysteine and alanine. Post-translational modification, and the formation of lanthionine or methyllanthionine rings, could partly expl ain the difference. Hybridization experiments showed that the organization of the gene cluster in pBAC105 responsible for the production of the bacter iocin is similar to that in pMRC01, which involves genes encoding modifying enzymes for lantibiotic biosynthesis and dual-function transporters. In bo th cases, the gene clusters are flanked by IS946 elements, suggesting an en bloc transposition. The findings from the isolation and molecular characte rization of the bacteriocin provide evidence for the lantibiotic nature of the two peptides.