Analyses génomiques comparatives de souches de Brevibacterium et étude de leurs interactions biotiques avec Hafnia alvei dans un fromage modèle

Abstract : The objective of this study was to better understand the molecular mechanisms of microbial adaptation to the cheese habitat by functional genomic approaches using Brevibacterium as a model microorganism. This bacterium is widely used for the manufacturing of cheese but its growth on the cheese surface is sometimes difficult to control.Comparative genomic analysis of 23 Brevibacterium strains, including 12 strains isolated from cheeses, revealed differences in genetic determinants involved in the growth on the cheese surface. Some of them are correlated to strain phylogeny and others are the result of gene transfers, especially those involved in iron acquisition and bacteriocin biosynthesis. We identified genomic islands corresponding to transfers of genes involved in iron acquisition between cheese-associated Brevibacterium strains and cheese-associated strains belonging to other genera. We also detected a conjugative transposon encoding bacteriocin production, which is present in cheese-associated Brevibacterium strains as well as in a cheese-associated Corynebacterium strain.Functional study of biotic interactions between Brevibacterium and Hafnia alvei, another cheese-ripening bacterium, was performed in a model cheese developed in this study. By coupling microbial, biochemical and transcriptomic (RNA-seq) analyses, we revealed several interaction mechanisms between these bacteria. These concern, in particular, iron acquisition, proteolysis, lipolysis, sulfur metabolism and D-galactonate catabolism. Our findings suggest that in the mutualistic relationship between some Brevibacterium strains and H. alvei, the latter stimulates Brevibacterium growth by the secretion of siderophores, which can be used by Brevibacterium to capture iron more efficiently. In return, Brevibacterium secretes lipases and proteases, which degrade cheese caseins and triglycerides into energetic substrates that stimulate H. alvei growth. This type of interaction is interesting to consider in the formulation of ripening cultures because it results in a better ability of all partners to colonize the cheese, and thus to generate the desired technological properties.
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Nguyen Phuong Pham. Analyses génomiques comparatives de souches de Brevibacterium et étude de leurs interactions biotiques avec Hafnia alvei dans un fromage modèle. Génie des procédés. Université Paris-Saclay, 2018. Français. ⟨NNT : 2018SACLA035⟩. ⟨tel-02136579⟩

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