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Rôle des systèmes toxine antitoxine de Sinorhizobium meliloti au cours de l’interaction symbiotique avec Medicago sp.

Abstract : The symbiotic interaction between the soil bacterium Sinorhizobium meliloti and the legumes plant Medicago sp. led to the development of a new root organ: the nodule. In this nodule differenciated bacteria into bacteroids, reducing atmospheric nitrogen into ammonia directly assimilated by the plant, thus promoting its nitrogen nutrition. In exchange, the plant, thanks to its photosynthetic activity, provides carbon compounds to the bacteroids. This mutual benefit association is however not permanent. Indeed, just weeks after the establishment of the symbiosis, senescence defined by a degradation of Bacteroides and plant cells, is observed. This stage of development is poorly understood in particularly about bacterial signal.The primary objective of this study was therefore to analyze the role of bacteroids in this symbiotic rupture. For this, we are particularly interested in the role of VapBC toxin antitoxin systems (TA) of S. meliloti. Indeed, in the literature, they are known to be involved in the stress response, persistence and / or bacterial death and the survival of the bacteria within the host cell. At first, we developed a global analysis of the role of 11 VapBC chromosomal systems in S. meliloti symbiotic interaction. After an in silico study, we studied the symbiotic phenotype with Medicago sp., Of each of the bacterial toxin mutants invalidation. Given the results, we, as a second step, developed a detail analysis of phenotypes obtained with two of these mutants: vapC5- and vapC7-.
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Justine Lipuma. Rôle des systèmes toxine antitoxine de Sinorhizobium meliloti au cours de l’interaction symbiotique avec Medicago sp.. Sciences agricoles. Université Nice Sophia Antipolis, 2015. Français. ⟨NNT : 2015NICE4044⟩. ⟨tel-03270764⟩

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