A BACTERIOCIN-LIKE PEPTIDE INDUCES BACTERIOCIN SYNTHESIS IN LACTOBACILLUS-PLANTARUM C-11

In this study, we show that bacteriocin production in Lactobacillus pl antarum C11 is an inducible process triggered by a secreted protein fa ctor produced by the bacteriocin producer itself, The induction factor was identified to be plantaricin A, a bacteriocin-like peptide whose gene (plnA) is located in the same operon as a two-component regulator y system (plnBCD). When e. plantarum C11 cultures were depleted for pl antaricin A, either by growing individual colonies on agar plates or b y starting a new culture with a highly diluted inoculum, no bacterioci n was produced during the following growth. When chemically synthesize d plantaricin A or purified bacterially produced plantaricin A was add ed to non-producing cultures, bacteriocin production was induced. Only 1 ng ml(-1) plantaricin A is sufficient to induce the bacteriocin pro duction in non-producing L. plantarum C11, and bacteriocin activity ap pears in the growth medium approximately 150 min after induction. Nort hern analyses, using a plnA-specific probe, demonstrated that plantari cin A is able to induce its own synthesis by transcription of the plnA BCD operon, and this is observed approximately 15 min after adding pla ntaricin A. Furthermore, heterologous expression of the plnABCD operon in a Lactobacillus sake strain showed that the conditioned growth med ium contained the active induction factor. Neither synthetic nor expre ssed plantaricin A from the heterologous system possesses any bacterio cin activity, suggesting that plantaricin A is primarily an induction factor and not a bacteriocin as claimed earlier.