title: Control of the transcription of a short gene encoding a cyclic peptide in Streptococcus thermophilus: a new quorum-sensing system?
abstract: Gram-positive bacteria secrete a variety of peptides that are often subjected to posttranslational modifications and that are either antimicrobials or pheromones involved in bacterial communication. Our objective was to identify peptides secreted by Streptococcus thermophilus, a nonpathogenic bacterium widely used in dairy technology in association with other bacteria, and to understand their potential roles in cell-cell communication. Using reverse-phase liquid chromatography, mass spectrometry, and Edman sequencing, we analyzed the culture supernatants of three S. thermophilus strains (CNRZ1066, LMG18311, and LMD-9) grown in a medium containing no peptides. We identified several peptides in the culture supernatants, some of them found with the three strains while others were specific to the LMD-9 strain. We focused our study on a new modified peptide secreted by S. thermophilus LMD-9 and designated Pep1357C. This peptide contains 9 amino acids and lost 2 Da in a posttranslational modification, most probably a dehydrogenation, leading to a linkage between the Lys2 and Trp6 residues. Production of Pep1357C and transcription of its encoding gene depend on both the medium composition and the growth phase. Furthermore, we demonstrated that transcription of the gene coding for Pep1357C is drastically decreased in mutants inactivated for the synthesis of a short hydrophobic peptide, a transcriptional regulator, or the oligopeptide transport system. Taken together, our results led us to deduce that the transcription of the Pep1357C-encoding gene is controlled by a new quorum-sensing system.
authors.affiliation: INRA, Unité de Biochimie Bactérienne, UR477, F-78350 Jouy en Josas, France.
authors.forename: Mariam
authors.initials: M
authors.lastname: Ibrahim
authors.forename: Alain
authors.initials: A
authors.lastname: Guillot
authors.forename: Francoise
authors.initials: F
authors.lastname: Wessner
authors.forename: Florence
authors.initials: F
authors.lastname: Algaron
authors.forename: Colette
authors.initials: C
authors.lastname: Besset
authors.forename: Pascal
authors.initials: P
authors.lastname: Courtin
authors.forename: Rozenn
authors.initials: R
authors.lastname: Gardan
authors.forename: Véronique
authors.initials: V
authors.lastname: Monnet
mesh_terms: D001426:Bacterial Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification; D002853:Chromatography, Liquid; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D013058:Mass Spectrometry; D009154:Mutation; D010456:Peptides, Cyclic / Q000096:biosynthesis* / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification; D011499:Protein Processing, Post-Translational; D053038:Quorum Sensing; D012329:RNA, Bacterial / Q000096:biosynthesis; D012333:RNA, Messenger / Q000096:biosynthesis; D020539:Sequence Analysis, Protein; D048249:Streptococcus thermophilus / Q000235:genetics* / Q000502:physiology*; D014158:Transcription, Genetic
chemical_list: D001426:Bacterial Proteins; D010456:Peptides, Cyclic; D012329:RNA, Bacterial; D012333:RNA, Messenger