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Andre GuillaumeResearch project of Dr Guillaume Andre The cell wall of lactic bacteria: a nanoscale view Although much is known about the structure and biosynthesis of bacterial cell walls, the three-dimensional organization, assembly, and interactions of the individual components remain poorly understood. At the cros-roads of nanotechnology and microbiology, I’m interested in gaining detailed insight into the nanometer-scale surface architecture and biophysical properties of two lactic acid bacteria, Lactococcus lactis and Lactobacillus plantarum, with an emphasis on three major cell wall components, i.e. peptidoglycan, teichoic acids, and cell wall polysaccharides. To reach this goal, we investigate the nanoscale properties of wild-type strains and of mutants altered in their cell wall components using advanced atomic force microscopy (AFM) techniques (live cell imaging, singl-molecule force spectroscopy (SMFS) of cell surface constituents). In collaboration with the Hols team (ISV-UCL) and in the frame of an ARC project, we recently measured the force and the dynamics of the LysM-peptidoglycan interaction using SMFS with LysM tips, and we established the method to detect and localize peptidoglycan on the surface of living bacteria. We then used high resolution topographic and recognition imaging to demonstrate that the L. lactis cell wall consists of 25 nm wide peptidoglycan cables perpendicular to the long axis of the cell, overlaid by a thin, compact polysaccharide pellicle [1]. We also combined SMFS with fluorescence microscopy to demonstrate that the distribution of wall teichoic acids in L. plantarum is highly polarized, and that this heterogeneity plays a key role in controlling cell morphogenesis (surface roughness, cell shape, cell elongation, and cell division) [2]. My work provides novel insight into the structure-function relationships of bacterial cell walls and shows that the combination of AFM with the use of bacterial mutants is a relevant platform for analyzing the spatial organization of cell walls constituents.
Imaging lactic bacteria: from structure to function. (a-c) Imaging the nanoscale organization of peptidoglycan in living Lactococcus lactis cells. (a) Topographic image of two dividing bacterial cells lacking cell wall exopolysaccharides. (b) Single-molecule recognition map (400 nm × 400 nm) recorded with an LysM probe in the square area shown in the topographic image; peptidoglycan molecules were detected (bright pixels) and found to be arranged as lines running parallel to the short cell axis (red lines). (c) Schematic views of the architecture of the L. lactis cell wall: the top cartoon emphasizes the two layers of the cell wall, i.e. periodic bands of peptidoglycan (blue) covered by cell wall polysaccharides (brown), while the bottom cartoon is an enlarged view of the peptidoglycan nanocables (blue) lying on the membrane (green). (d-f) Imaging the heterogeneous distribution of wall teichoic acids (WTAs) in Lactobacillus plantarum. (d) Topographic image of a single L. plantarum cell revealing a highly polarized surface morphology, the poles being much smoother than the side walls. (e) Single-molecule recognition map (400 nm × 400 nm) recorded with a lectin probe in the square area shown in the topographic image; WTAs were massively detected on the side walls (bright pixels) but essentially lacking on the poles (dark pixels). (f) Schematic view of the architecture of the L. plantarum cell wall: WTAs localize exclusively on the side walls (red), correlating with a rough surface morphology. [1] Andre, G. et al. (2010) Imaging the nanoscale organization of peptidoglycan in living Lactococcus lactis cells. Nat. Commun. 1:27 doi:10.1038/ncomms1027
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9/03/2011
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