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J. Bacteriol., May 1995, 2387-2395, Vol 177, No. 9
E Hoiczyk and W Baumeister
The cell walls of four gliding filamentous Oscillatoriaceae species
comprising three different genera were studied by freeze substitution,
freeze fracturing, and negative staining. In all species, the multilayered
gram-negative cell wall is covered with a complex external double layer.
The first layer is a tetragonal crystalline S-layer anchored on the outer
membrane. The second array is formed by parallel, helically arranged
surface fibrils with diameters of 8 to 12 nm. These fibrils have a serrated
appearance in cross sections. In all cases, the orientation of the surface
fibrils correlates with the sense of revolution of the filaments during
gliding, i.e., clockwise in both Phormidium strains and counterclockwise in
Oscillatoria princeps and Lyngbya aeruginosa. The lack of longitudinal
corrugations or contractions of the surface fibrils and the identical
appearances of motile and nonmotile filaments suggest that this structure
plays a passive screw thread role in gliding. It is hypothesized that the
necessary propulsive force is generated by shear forces between the surface
fibrils and the continuing flow of secreted extracellular slime.
Furthermore, the so-called junctional pores seem to be the extrusion sites
of the slime. In motile cells, these pores exhibit a different staining
behavior than that seen in nonmotile ones. In the former, the channels of
the pores are filled with electron-dense material, whereas in the latter,
the channels appear comparatively empty, highly contrasting the
peptidoglycan. Finally, the presence of regular surface structures in other
gliding prokaryotes is considered an indication that comparable structures
are general features of the cell walls of gliding microbes.
Copyright © 1995, American Society for Microbiology
Envelope structure of four gliding filamentous cyanobacteria
Max-Planck-Institut fur Biochemie, Martinsried, Germany.
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