SHAPE · Control of cell morphogenesis: Bacterial cell wall and actin-cytoskeleton

Control of cell morphogenesis: Bacterial cell wall and actin-cytoskeleton

The aim of this project, realized at the Institut National de la Recherche Agronomique (INRA) at Jouy-en-Josas (France), is to determine the role(s) of the bacterial actine-like cytoskeleton (MreB) and more specifically the factors controlling bacterial morphogenesis. The current view is that of a dynamic subcellular organization in which the cytoskeleton would plays a central organiser role by spatially coordinating key cellular functions. For this, MreBs might be connected to effectors proteins that serve as ‘interface’ between the cytoskeleton and other cellular networks. In addition, it is thought that MreB filaments may serve as an organizer or tracking device for the movement of cell wall (CW) synthesizing machineries and for the targeting of many proteins to their sites of biological function, thus playing a role analogous to the eukaryotic cytoskeleton in macromolecular trafficking. Thus, a major challenge is to identify proteins that might move along or that are positioned by the actin-like filaments or, conversely, proteins that could regulate or modulate MreBs dynamics or function. In order to determine the roles of MreBs and other associated factors controlling bacterial morphogenesis, I conducted a trans-disciplinary approach using the model Gram-positive bacterium Bacillus subtilis. I used a combination of genetic, microscopic, biochemistry, biophysics, transcriptomic and mathematical modeling approaches. My work has been following two main axes of research: 1- unmasking MreB-binding proteins, targets and effectors and 2- determining the spatio-temporal organization of MreB cytoskeleton and associated proteins in relation with the structure and the regulation properties of the bacterial cell wall. Following this plan, several major discoveries were made. First, I unveiled several proteins interacting with MreB including a previously uncharacterized protein required for synthesis of an essential constituent of the CW precursor. Second I have revisited the in vivo dynamics of MreB through advanced microscopy techniques revealing an unexpected behavior that forced the field to completely rethink the model of MreB mode of action. Altogether, my data support a model in which 1- membrane-associated MreB forms discrete particles that act as recruitment platforms, dragged along by CW-synthesizing complexes during the processive assembly of the CW, and 2- soluble MreBs also organize intra-cellular steps of peptidoglycan synthesis in the cytoplasm to feed the membrane-associated cell wall synthesizing machineries. Taken together, the results have greatly modified our understanding of MreB functions and its relationship with the control of the shape and the CW synthesis and maintenance and will have a lasting impact into the field. On a personal point of view, this reintegration period strongly benefits from the IRG that helped me hiring work force, disseminating my works abroad in international congresses and altogether strengthening my profile, leading to my recruitment on a permanent position at the host institution.

Data: CORDIS, © European Union