C3-P-07Cell surface ofMycoplasma mobile,gliding bacterium, observed by Quick-Freeze Deep-Etch Replica Electron Microscopy

Abstract

Mycoplasma mobile, a fish pathogen belonging to a class of wall-less bacteria, glides on solid surfaces in the direction of a membrane protrusion at a cell pole by a unique mechanism involving, notably, huge surface proteins [1]. The molecular shapes of those proteins have been previously visualized but still few information is available about their assemblies on the mycoplasma surface. To clarify this point, quick-freeze deep-etch replication (QFDE) method was performed by using mica-flakes as a solid support for cells [2, 3]. This method allowed us to visualize, for the first time, and starfish-shaped structures on the cell surface, at a very high resolution. Moreover, it allowed us to freeze the gliding movement of cells (see the attached figure, right image is a magnified area of the left image, on which leg-shaped structures are pointed by arrows). The molecular shape and dimensions of the surface structures are consistent with those of gliding proteins. The images we obtained here may be the first step into the three dimensional description of the gliding mechanism, at a molecular level.