Le gène cse, de création récente, code une hydrolase du peptidoglycane impliquée dans la séparation des cellules de Streptococcus thermophilus

Abstract : Streptococcus thermophilus is a lactic bacteria used a stater of fermentation in dairy factories for the production of yogurt and many cheeses. S. thermophilus grows as chains of ovoid cells. However, the genetic basis of S. thermophilus cell separation is still unknown. A S. thermophilus mutant displaying extremely long chains of cells was characterized and demonstrated to be impaired a gene that we named cse for cell separation. The originality of this gene is that cse creation resulted from domain shuffling. Indeed, the analysis has revealed that its 5?extremity has homology with that of sip from S. salivarius, while its 3?extremity shares homology with pcsB from S. thermophilus.The cse gene specific from S. thermophilus, encodes a modular protein. The N-terminal end of Cse contains a secretion signal and cell-wall binding LysM domain. Its C-terminal end includes a CHAP domain found in bacterial cell-wall hydrolases. In this study, the localization of Cse on S. thermophilus cell surface has been undertaken by immunogold electron and immunofluorescence microscopies using of antibodies raised against this protein. Immunolocalization shows that the presence of the Cse protein at mature septa. Moreover, the CHAP domain of Cse exhibits a lytic activity on the cell wall of S. thermophilus that has been demonstrated by zymogram. Additionally, RP-HPLC analysis of muropeptides released from S. thermophilus after digestion with the CHAP domain shows that Cse is a cell wall hydrolase that can function as an endopeptidase. Alltogether, these results suggest that Cse is a major cell wall hydrolase involved in daughter cell separation of S. thermophilus.
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Séverine Layec. Le gène cse, de création récente, code une hydrolase du peptidoglycane impliquée dans la séparation des cellules de Streptococcus thermophilus. Génomique, Transcriptomique et Protéomique [q-bio.GN]. Université Henri Poincaré - Nancy 1, 2008. Français. ⟨NNT : 2008NAN10066⟩. ⟨tel-01748447⟩

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