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The constant gene orf14.9, which belongs to the variable eps (exopolysaccharide) cluster, is involved in the cell growth of Streptococcus thermophilus

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In Streptococcus thermophilus, the eps clusters involved in exopolysaccharide (EPS) biosynthesis are very polymorphic, nevertheless they all contain a highly conserved sequence corresponding to that of orf14.9. This open reading frame (ORF) is transcribed in a reverse direction with respect to eps genes. Amino acid sequence analysis showed a possible transmembrane location of the putative Orf14.9 protein but did not permit a proposed function. Insertional mutants of orf14.9 were obtained in strains NST2280 and A054 of S. thermophilus. EPS yields of these mutants are similar to those of their respective wild strains, suggesting that orf14.9 does not modify the quantity of produced EPS. Growth parameter determination for wild strains and their respective mutants showed that orf14.9 is involved in the cell growth of S. thermophilus.Key words: Streptococcus thermophilus, eps cluster, orf14.9, sequence analysis, exopolysaccharide biosynthesis, cell growth.

Les clusters eps de Streptococcus thermophilus, impliqués dans la biosynthèse des exopolysaccharides (EPS), présentent une variabilité génétique importante. Néanmoins, tous se caractérisent par la présence d'une séquence hautement conservée, orf14.9. Cette ORF est orientée en sens inverse par rapport aux ORF opéroniques du cluster eps et est transcrite. Les analyses de séquence suggèrent que la protéine potentielle Orf14.9 est transmembranaire mais de fonction inconnue. Des mutants insertionnels d'orf14.9 ont été réalisés chez S. thermophilus NST2280 et A054. Chez ces mutants, le taux d'EPS produit ne présente pas de différence statistiquement significative avec le taux d'EPS produit par leurs souches sauvages respectives. Chez ces mutants, l'absence de l'orf14.9 fonctionnelle ne modifie donc pas la quantité d'EPS produit. La détermination des paramètres de la croissance pour les souches sauvages et leurs mutants respectifs montre qu'orf14.9 est impliquée dans la croissance cellulaire de S. thermophilus.Mots clés : Streptococcus thermophilus, cluster eps, orf14.9, analyse de séquence, biosynthèse des exopolysaccharides, croissance cellulaire.

Document Type: Research Article

Publication date: 2006-09-01

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  • Published since 1954, this monthly journal contains new research in the field of microbiology including applied microbiology and biotechnology; microbial structure and function; fungi and other eucaryotic protists; infection and immunity; microbial ecology; physiology, metabolism and enzymology; and virology, genetics, and molecular biology. It also publishes review articles and notes on an occasional basis, contributed by recognized scientists worldwide.
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