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Caractérisation de la variabilité du système protéolytique de surface de la bactérie lactique Streptococcus thermophilus

Abstract : The variability of the cell envelope-associated proteolytic system was studied in 30 strains of St. thermophilus. Variations in strains consist in the presence or absence of the gene prtS, the presence of two allelic forms of prtS, the presence of an anchored and/or soluble form of the protease PrtS and in the variable expression of the gene prtS and other genes involved mainly in nitrogen metabolism, thus in the variability of the regulation genetic of this system. Expression of the genes prtS, pepX, pepC, pepN, amiA1CDEF, dtpT, livJHMGF, ilvC, ilvDBN, bcaT, ackA, ldh, codY and relA was quantified in the PB302 and PB18O strains. The strain PB302 is representative of strains which exhibit a rapid growth in milk. The strain PB18O is representative those with intermediate growth in milk. In M17 medium, where both strains have similar growth, little difference in the expression of genes tested was observed. Conversely, the two strains did not express the selected genes in the same way when grown in milk. Overall, the difference in growth observed between strains in milk could result from variable proteolytic activities and variable expression of genes encoding, for example, the proteinase PrtS, the regulator CodY, transporters of oligo- or di-tri- peptides (Ami or DtpT) or branched chain amino acids, or BCAA (LivJ) and enzymes in the biosynthetic pathway of BCAA (IlvC, IlvB et BcaT) which are necessary for growth in milk. All these genes have a potential CodY box at the upstream of their promoter and could therefore belong to the regulon CodY.
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Submitted on : Thursday, March 29, 2018 - 12:17:52 PM
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  • HAL Id : tel-01749494, version 1


Wessam Galia. Caractérisation de la variabilité du système protéolytique de surface de la bactérie lactique Streptococcus thermophilus. Sciences agricoles. Institut National Polytechnique de Lorraine, 2011. Français. ⟨NNT : 2011INPL053N⟩. ⟨tel-01749494⟩



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