Interactions phage-hôte et caractérisation de la résistance aux phages chez Lactococcus lactis

Authors: Samson, Julie
Advisor: Moineau, Sylvain
Abstract: Bacteria and phages are continuously challenging each other and evolve in most ecosystems. Many strategies have been adapted by both of them to reach an equilibrium state. On one side, phages can infect efficiently and rapidly their bacterial host. On the other side, bacteria have acquired antiphage mechanisms to resist phage infection and limit their propagation such as abortive infection mechanisms (Abi). Specifically, the AbiQ antiphage system was isolated from Lactococcus lactis. This bacterium is used to produce an array of fermented dairy products. Even if this environment is tightly controlled, phages are ubiquitous in milk and in factories, and they can affect fermentations. The AbiQ antiphage system ressembles to a toxin-antitoxin (TA) system, but its mode of action is still unknown. In this study, three objectives were persued in order to better understand the relationship between Lactococcus lactis and its phages. First, the phage 949 genome, a member of a rare lactophage group that bears its name, was sequenced and characterized. A genome comparison of all lactococcal phages sequenced to date was done to confirm the current phage classification. In the second objective, we have confirmed that AbiQ is indeed a toxin-antitoxin system. Experiments were performed to demonstrate that this TA mechanism is composed of a RNA antitoxin and a protein toxin with ribonuclease activity. In the third objective, the effect of AbiQ on the phage replication was evaluated. By isolating phage mutants able to escape the mechanism, different phage targets were identified. Understanding the phage-host relationships is the key to develop efficient tools to reduce phage infection in industrial settings or to limit the development of phage resistance in other applications such as in phage therapy.
Document Type: Thèse de doctorat
Issue Date: 2013
Open Access Date: 19 April 2018
Grantor: Université Laval
Collection:Thèses et mémoires

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