title: Extracellular life cycle of ComS, the competence-stimulating peptide of Streptococcus thermophilus.
abstract: In streptococci, ComX is the alternative sigma factor controlling the transcription of the genes encoding the genetic transformation machinery. In Streptococcus thermophilus, comX transcription is controlled by a complex consisting of a transcriptional regulator of the Rgg family, ComR, and a signaling peptide, ComS, which controls ComR activity. Following its initial production, ComS is processed, secreted, and imported back into the cell by the Ami oligopeptide transporter. We characterized these steps and the partners interacting with ComS during its extracellular circuit in more detail. We identified the mature form of ComS and demonstrated the involvement of the membrane protease Eep in ComS processing. We found that ComS was secreted but probably not released into the extracellular medium. Natural competence was first discovered in a chemically defined medium without peptides. We show here that the presence of a high concentration of nutritional peptides in the medium prevents the triggering of competence. In milk, the ecological niche of S. thermophilus, competence was found to be functional, suggesting that the concentration of nutritional peptides was too low to interfere with ComR activation. The kinetics of expression of the comS, comR, and comX genes and of a late competence gene, dprA, in cultures inoculated at different initial densities revealed that the activation mechanism of ComR by ComS is more a timing device than a quorum-sensing mechanism sensu stricto. We concluded that the ComS extracellular circuit facilitates tight control over the triggering of competence in S. thermophilus.
authors: INRA, UMR1319 MICALIS, Jouy en Josas, France. rozenn.gardan@jouy.inra.fr
authors: Rozenn
authors: R
authors: Gardan
authors: Colette
authors: C
authors: Besset
authors: Christophe
authors: C
authors: Gitton
authors: Alain
authors: A
authors: Guillot
authors: Laetitia
authors: L
authors: Fontaine
authors: Pascal
authors: P
authors: Hols
authors: Véronique
authors: V
authors: Monnet
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D001693:Biological Transport, Active; D002462:Cell Membrane / Q000502:physiology; D002853:Chromatography, Liquid; D061269:DNA Transformation Competence / Q000502:physiology; D015964:Gene Expression Regulation, Bacterial / Q000502:physiology*; D008156:Luciferases; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D009154:Mutation; D053038:Quorum Sensing; D012808:Sigma Factor / Q000235:genetics / Q000378:metabolism; D048249:Streptococcus thermophilus / Q000235:genetics / Q000378:metabolism*; D053719:Tandem Mass Spectrometry; D013997:Time Factors; D014158:Transcription, Genetic / Q000502:physiology
chemical_list: D001426:Bacterial Proteins; D008565:Membrane Proteins; D012808:Sigma Factor; D008156:Luciferases
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