Click and Collect at high resolution: a new strategy to unlock the secrets of cell wall synthesis
Cecile Morlot, Institut de Biologie Structurale, CNRS/CEA/UGA, Grenoble, France
Host: Sérgio Filipe, UCIBIO NOVA
ZOOM link: https://bit.ly/GuestSeminarsUCIBIO
ID da reunião: 865 7786 0516
Abstract: The cell wall is a three-dimensional sugar and peptide network that surrounds the bacterial cell. It confers a cell shape adapted to the ecological niche of the bacterium and protects it against mechanical stress exerted by the environment. Cell wall synthesis and integrity are thus essential for bacterial proliferation and survival. Despite the importance of these fundamental processes, which constitute sources of antibiotic targets, we still poorly understand how the cell wall is assembled and remodeled in space and time to ensure proper cell division, shape and integrity. This is particularly true for ovoid-shaped bacteria such as streptococci and enterococci, in which two different modes of cell wall synthesis, dedicated to cell division and elongation, are confined to an annular region with nanometric dimensions at midcell.
Fluorescence microscopy is a method of choice to investigate cell wall assembly but it suffers from two major drawbacks. First, the newly synthesized material must be labeled with a probe that will not perturb the physiological process. Second, the physical properties of light limit the resolution to about 250 nm, which approximates the dimensions of the cell wall synthesis region. We have met these two challenges by combining metabolic cell wall labeling (using click chemistry) and super-resolution fluorescence microscopy (dSTORM) in the ovoid-shaped human pathogen Streptococcus pneumoniae. Our nanoscale-resolution data (~ 30 nm) unraveled unprecedented spatio-temporal features of cell wall assembly and fate along the cell cycle. It provided geometrical and kinetic parameters of cell wall synthesis that we further used to simulate the morphogenesis of the ovoid cell in silico.
I will present our methodological strategy and the major insights that our experimental and modeling analyses revealed into cell wall synthesis and morphogenesis in ovococci.
Short CV: I started studying morphogenesis and division processes in Streptococcus pneumoniae during my Ph.D. at the Institute for Structural Biology (2000-2003, IBS, Grenoble, France). Under the supervision of Thierry Vernet, I investigated the cellular localization of the Penicillin-Binding Proteins and the structure the cell wall hydrolase DacA.
For my 1st post-doc, I joined the Grenoble EMBL outstation in Stephen Cusack’s group (2004-2007, EMBL, Grenoble, France) where I characterized the structure of a protein complex involved in neuron development in humans.
For my 2nd post-doc, I joined the group of David Rudner at Harvard Medical School (2007-2010, HMS, Boston, USA) to study the function of two macromolecular complexes (SpoIIIA-SpoIIQ and SpoIIP-SpoIID) during sporulation in Bacillus subtilis.
I was recruited in 2010 as a CNRS researcher and since January 2021, I took the head of the Pneumococcus group at the IBS (Grenoble, France). My group employs complementary techniques in microbial genetics, biochemistry, structural biology and cell imaging (including super-resolution microscopy) to study the mechanisms of cell morphogenesis and division during vegetative growth and sporulation. We address in particular the synthesis of the two main components of the cell wall in the human pathogen S. pneumoniae, the peptidoglycan and the teichoic acids. In parallel, we study the structure and function of the SpoIIIA-SpoIIQ complex, a putative new secretion system required for spore development in B. subtilis.