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Wet-surface-enhanced ellipsometric contrast microscopy identifies slime as a major adhesion factor during bacterial surface motility

A. Ducret, M.-P. Valignat, F. Mouhamar, T. Mignot, and O. Theodoly

PNAS 109, 10036-10041 (2012) [Accès à la revue]

Une nouvelle technique d’imagerie, la microscopie wet-SEEC est utilisée. Elle permet d’imager de façon quantitative des films d’épaisseur nanométrique et d'étudier le rôle de la matrice extra-cellulaire dans un phénomène de motilité bactérienne.

Abstract: In biology, the Extra-Cellular Matrix (ECM) promotes both cell adhesion and specific recognition, which is essential for central developmental processes in both eukaryotes and prokaryotes. However, live studies of the dynamic interactions between cells and the ECM, for example during motility, have been greatly impaired by imaging limitations: mostly the ability to observe the ECM at high resolution in absence of specific staining by live microscopy. To solve this problem, we developed a novel technique, Wet-SEEC, which magnifies the contrast of transparent organic materials deposited on a substrate (Wet-surf) with exquisite sensitivity. We show that Wet-SEEC allows both the observation of unprocessed nanofilms as low as 0.2 nm thick and their accurate 3D topographic reconstructions, directly by standard light microscopy. We next employed Wet-SEEC to image slime secretion, a poorly defined property of many prokaryotic and eukaryotic organisms that move across solid surfaces in absence of obvious extracellular appendages (gliding). Using combined Wet-SEEC and fluorescent-staining experiments, we observed slime deposition by gliding Myxococcus xanthus cells at unprecedented resolution. All together, the results revealed that in this bacterium, slime associates preferentially with the outermost components of the motility machinery and promotes its adhesion to the substrate on the ventral side of the cell. Strikingly, analogous roles have been proposed for the extracellular proteoglycans of gliding diatoms and apicomplexa, suggesting that slime deposition is a general means for gliding organisms to adhere and move over surfaces.

Thème : Thème 2007-2010 : Motilité

Equipe : Mécanismes Fondamentaux de l'adhésion (A & I)