A fundamental question in cell biology is how cells determine their shape. Each life form is surrounded by boundary layers that protect, communicate with the environment, and may confer shape and rigidity. However, little is known about the mechanisms determining cell shape, and the broader questions concerning morphogenesis are the same in prokaryotic and eukaryotic systems. How is cell shape regulated temporally and spatially? How is structural information acquired and maintained? In bacteria, the tough external peptidoglycan cell wall is known to be a primary determinant of cell shape. But despite decades of studies, both its ultra-structure and the molecular mechanisms that control wall morphogenesis are poorly understood. A radical change recently occurs with the discovery of a bacterial actin-like cytoskeleton as a primary determinant of cell wall biogenesis. Moreover, actin homologues (MreB family) are not only involved in cell morphogenesis but also in DNA segregation and cell polarity, suggesting a key function in cell development. However, the mechanistic details and the effectors used by MreB proteins to fulfil these roles remain to be elucidated. The general aims of this project are to elucidate the factors controlling bacterial cell wall morphogenesis and to determine the different functions of the bacterial cytoskeleton and the mechanisms underlying them. For this, an interdisciplinary approach combining the methods of genetic, microscopy, biochemistry, physico-chemistry and mathematical modelling will be used.