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Journal of Bacteriology, July 2009, p. 4647-4655, Vol. 191, No. 14
0021-9193/09/$08.00+0     doi:10.1128/JB.00257-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

The Oligopeptide Transport System Is Essential for the Development of Natural Competence in Streptococcus thermophilus Strain LMD-9{triangledown}

Rozenn Gardan,1* Colette Besset,1 Alain Guillot,2 Christophe Gitton,1 and Véronique Monnet1,2

INRA, Unité de Biochimie Bactérienne, UR477, F-78350 Jouy en Josas, France,1 INRA, PAPPSO, F-78350 Jouy en Josas, France2

Received 26 February 2009/ Accepted 7 May 2009

In gram-positive bacteria, oligopeptide transport systems, called Opp or Ami, play a role in nutrition but are also involved in the internalization of signaling peptides that take part in the functioning of quorum-sensing pathways. Our objective was to reveal functions that are controlled by Ami via quorum-sensing mechanisms in Streptococcus thermophilus, a nonpathogenic bacterium widely used in dairy technology in association with other bacteria. Using a label-free proteomic approach combining one-dimensional electrophoresis with liquid chromatography-tandem mass spectrometry analysis, we compared the proteome of the S. thermophilus LMD-9 to that of a mutant deleted for the subunits C, D, and E of the ami operon. Both strains were grown in a chemically defined medium (CDM) without peptides. We focused our attention on proteins that were no more detected in the ami deletion mutant. In addition to the three subunits of the Ami transporter, 17 proteins fulfilled this criterion and, among them, 7 were similar to proteins that have been identified as essential for transformation in S. pneumoniae. These results led us to find a condition of growth, the early exponential state in CDM, that allows natural transformation in S. thermophilus LMD-9 to turn on spontaneously. Cells were not competent in M17 rich medium. Furthermore, we demonstrated that the Ami transporter controls the triggering of the competence state through the control of the transcription of comX, itself controlling the transcription of late competence genes. We also showed that one of the two oligopeptide-binding proteins of strain LMD-9 plays the predominant role in the control of competence.

* Corresponding author. Mailing address: INRA, Unité de Biochimie Bactérienne, UR477, F-78350 Jouy en Josas, France. Phone: 33-1-34-65-27-70. Fax: 33-1-34-65-21-63. E-mail: rozenn.gardan{at}jouy.inra.fr

{triangledown} Published ahead of print on 15 May 2009.

Journal of Bacteriology, July 2009, p. 4647-4655, Vol. 191, No. 14
0021-9193/09/$08.00+0     doi:10.1128/JB.00257-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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