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Polymorphisme génétique du Locus eps (Exopolysaccharide) chez la bactérie lactique Streptococcus thermophilus : évolution rapide par remplacement de séquences

Abstract : The texture of dairy products resulting from lactic fermentation is obtained by the presence of exopolysaccharides excreted by the used lactic acid bacteria. These exopolysaccharides are required for the smoothness of the product. The chromosome region involved in the synthesis of exopolysaccharides synthesis in Streptococcus thermophilus is called eps locus. This region is very variable. S. thermophilus is a lactic acid bacterium used in coculture with other lactic acid bacteria such as Lactococcus lactis (used in cheese production) or Lactobacillus delbrueckii subsp. bulgaricus (used in yoghurt production). The eps locus represents a model of the implication of intra- and interspecific horizontal transfer in the origin of S. thermophilus polymorphism. Study of the eps loci of 3 S. thermophilus strains, CNRZ368, NST2280 and IP6757, allowed to reveal a large variability of this locus caused by horizontal transfers. S. thermophilus CNRZ368 contains a 32.5 kb eps locus including a 13.6 kb region which could originate from L. lactis. Moreover, the eps loci of 2 very related strains, IP6757 and NST2280, are very different. The comparison of the sequences of 27 kb and 19.2 kb eps loci of IP6757 and NST2280 S. thermophilus strains respectively shows two regions with high homology separated by a specific-strain region. These results, associated with the comparison of the eps loci of other phylogenetically related strains of IP6757 and NST2280, indicate that the eps locus of an IP6757 ancestor should have quickly evolved by acquisition, from an other bacterium of the lactic flora, and replacement of a part of its locus.
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https://hal.univ-lorraine.fr/tel-01746845
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Submitted on : Thursday, March 29, 2018 - 10:45:59 AM
Last modification on : Wednesday, October 14, 2020 - 3:57:40 AM

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  • HAL Id : tel-01746845, version 1

Citation

Arnaud Pluvinet. Polymorphisme génétique du Locus eps (Exopolysaccharide) chez la bactérie lactique Streptococcus thermophilus : évolution rapide par remplacement de séquences. Ingénierie des aliments. Université Henri Poincaré - Nancy 1, 2003. Français. ⟨NNT : 2003NAN10170⟩. ⟨tel-01746845⟩

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