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Réseaux de régulation chez Escherichia coli

Guillaume Baptist 1
1 IBIS - Modeling, simulation, measurement, and control of bacterial regulatory networks
LAPM - Laboratoire Adaptation et pathogénie des micro-organismes [Grenoble], Inria Grenoble - Rhône-Alpes, Institut Jean Roget
Abstract : The adaptation of bacteria to changes in their environment is controlled by a large and complex regulatory network involving many different actors and modules. In this work, we have studied a specific module controlling the adaptation of Escherichia coli to a change in carbon sources. In a medium containing glucose and acetate, growth is divided into two phases : the bacteria preferentially use glucose and start to metabolize acetate only after glucose exhaustion. Indeed, the presence of glucose represses the transcription of a gene needed for growth on acetate : the acs gene (coding for acetyl-CoA synthetase). The regulatory mechanism involves the Crp-cAMP regulator and the phosphate transfer system (PTS), which is responsible for glucose import. Several models describe the cascade of molecular reactions responsible for this « catabolite repression ». However, our work shows that many of our experimental observations are incorrectly predicted by current models. These models have to be amended.We use transcriptional fusion, i.e., the fusion of a promoter region upstream of a reporter gene (GFP, luciferase), to measure the dynamics of gene expression in different genetic backgrounds and environmental conditions. Observations at the population level are corroborated by similar measurements at the single cell level. We use this same technology to construct small synthetic systems that probe further aspects of the phenomenon of catabolite repression. We have thus created a genetic toggle switch controlled by the glycolytic flux and we have built an inter-cellular communication system mediated by cAMP. Finally, we propose a novel way to measure the metabolic state of cells by using the energy dependence of the luciferase enzyme.
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Guillaume Baptist. Réseaux de régulation chez Escherichia coli. Sciences agricoles. Université de Grenoble, 2012. Français. ⟨NNT : 2012GRENV040⟩. ⟨tel-00772446v2⟩

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