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Diversité des bactériophages infectant la bactérie lactique Oenococcus oeni, responsable de la fermentation malolactique des vins

Abstract : Bacteriophages are responsible for the predation of bacteria. They pose an ever-present threat to the food industries because they invade and destroy the starter and affect production. Their destructive potential is currently difficult to establish during spontaneous production of wine. Malolactic fermentation (MLF) represents a main stage in the winemaking process, and is essentially driven by the lactic acid bacterium (LAB) Oenococcus oeni. A rapid and efficient FML is essential to optimize wine quality and typicity, as sales rely on top-quality products. Up to now, this essential step is not controlled, and this results from the limited growth of MLF bacteria in wine, due to stressing conditions. Inoculation of commercial bacterial starter cultures is a strategy to improve MLF control, and will allow a rapid and complete fermentation. However, despite these evolutions, sluggish or complete failures of MLF are still reported by wine farmers, either during spontaneous or directed fermentations. Such cases suggest that additional factors need to be identified. The outline of this thesis was to demonstrate the occurrence of phages infecting O. oeni in the ecosystem and provide essential information regarding phage diversity. We analyzed prophage diversity through comparative genomics and demonstrated that lysogeny is widespread. Four prophage groups were identified according to the integrase gene sequence and attachment site used for site specific recombination. The relevance of the classification scheme was verified through the analysis of a panel of 40 phages isolated from wine and must. We suggest that lysogeny helps O. oeni to cope with stress and phage attack, through the presence of specific anti-phage mechanisms harbored by the prophages. The stability of lysogens during inoculation in wine, and the possible release of lytic particules have to be considered during spontaneous or directed MLF. They are expected to shape the population.
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Fety Jaomanjaka. Diversité des bactériophages infectant la bactérie lactique Oenococcus oeni, responsable de la fermentation malolactique des vins. Sciences agricoles. Université de Bordeaux, 2014. Français. ⟨NNT : 2014BORD0394⟩. ⟨tel-01968007⟩

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