Induction of Plantaricin Production inLactobacillus plantarumNC8 after Coculture with Specific Gram-Positive Bacteria Is Mediated by an Autoinduction Mechanism

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Abstract
Plantaricin NC8 (PLNC8), a coculture-inducible two-peptide bacteriocin from Lactobacillus plantarum NC8, has recently been purified and genetically characterized. Analysis of an 8.1-kb NC8 DNA region downstream of the PLNC8 operon revealed the presence of at least four operons involved in bacteriocin production, showing high homology to the plantaricin cluster in L. plantarum C11. However, we found a three-component regulatory operon involving a quorum-sensing mechanism. Two of these components, the induction factor (PLNC8IF) and the histidine kinase, are novel, while the response regulator is identical to PlnD from C11. Homologous expression of plNC8IF in NC8 allowed constitutive bacteriocin production. Heterologous expression of this gene in Lactococcus lactis MG1363 produced supernatants which promoted bacteriocin production in NC8. Reverse transcription-PCR studies indicated that cocultivation of NC8 with inducing cells promoted transcription of the bacteriocin and regulatory operons in NC8. An identical result was obtained after addition of an external source of PLNC8IF. We propose that the presence of specific bacteria could act as an environmental signal that is able to switch on bacteriocin production in L. plantarum NC8 via a quorum-sensing mechanism mediated by PLNC8IF.