Summary : How organisms sense the environment and adapt to different situations, regulating gene expression, is a fundamental question of biology. The most important machinery used in bacteria for the signal transduction is composed by two-component and phosphorelay systems (TCS). In general, TCS allow cells to adapt to changing conditions by modifying cellular physiology, including initiating programs of gene expression, catalyzing reactions, or modifying protein-protein interactions. In alpha-proteobacteria proteins of the signal transduction systems are strongly connected with essential aspects of bacterial life such as cell cycle regulation, quorum sensing and virulence. In this HDR dissertation the cell cycle regulation in alpha proteobacteria is analyzed starting from the discovery of a model circuit that explains cell cycle progression in Caulobacter crescentus ; then this model is expanded to closely related bacteria, the alpha proteobacteria, underlying common features and also different behaviors. Finally the knowledge of cell cycle regulation is experimentally tested on another model system, belonging to alphas, Sinorhizobium meliloti. The relationship between the cell cycle machinery and the process of bacteroids formation are discussed suggesting a complex and fascinating role of the cell cycle circuit during infection.
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