JB Accepts, published online ahead of print on 10 August 2007

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J. Bacteriol. doi:10.1128/JB.00966-07
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Quorum-Sensing regulation of the production of Blp bacteriocins in Streptococcus thermophilus

Laetitia Fontaine, Céline Boutry, Eric Guédon, Alain Guillot, Mariam Ibrahim, Benoît Grossiord, and Pascal Hols^*

Unité de Génétique, Institut des Sciences de la Vie, Université catholique de Louvain, Place Croix du Sud 5, B-1348 Louvain-la-Neuve, Belgium, Institut National de la Recherche Agronomique (INRA), Unité de Génétique Microbienne, Unité de Biochimie Bactérienne, Domaine de Vilvert, 78350 Jouy-en-Josas, France, and Laboratoire de Microbiologie et de Biochimie Appliquées (LMBA), UMR 5248 CBMN, CNRS-Université de Bordeaux 1-ENITAB, F-33170 Gradignan, France

^* To whom correspondence should be addressed. Email: hols{at}gene.ucl.ac.be.

The blp gene cluster identified in the genome sequences of S. thermophilus LMG18311, CNRZ1066, and LMD-9 (Stblp) displays all the characteristics of a Class II bacteriocin locus. In the present study, we showed that the Stblp locus is only fully functional in strain LMD-9 and regulates the production of antimicrobial peptides that inhibit strains LMG18311 and CNRZ1066. The Stblp cluster of LMD-9 contains 23 genes that are transcriptionally organized in six operons: StblpABC (peptide transporter genes and pheromone gene), StblpRH (two-component regulatory system genes), StblpD-orf1, StblpU-orf3 and StblpE-F (bacteriocin precursors and immunity genes), and StblpG-X (unknown function). All the operons, except the regulatory unit StblpRH, were shown to be co-regulated at the transcriptional level by a quorum-sensing mechanism involving the mature pheromone StBlpC*, which was extracellularly detected as two active forms (30 and 19 aa). These operons are differentially transcribed depending on growth phase and pheromone concentration. They all contain a motif with two imperfect direct repeats in their mapped promoter regions that could serve as binding sites of the response regulator StBlpR. By constructing deletion mutants, the Stblp locus of strain LMD-9 was shown to encode all the essential functions associated with bacteriocin production, quorum-sensing regulation, and immunity.

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