The cell wall of lactic bacteria : a nanoscale view

André, Guillaume
(2010)

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Authors
  • André, GuillaumeUCLouvain
    author
Supervisors
Dufrêne, Yves
 ;
Hols, Pascal
Abstract
(en) 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 cross-roads of nanotechnology and microbiology, this thesis aims at 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 investigated 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, single-molecule force spectroscopy (SMFS) of cell surface constituents). We first 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. Lastly, we 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). This 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.
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André, G. (2010). The cell wall of lactic bacteria : a nanoscale view. https://hdl.handle.net/2078.5/148305