Bacterial cell envelope classes

Figure 1 Schematic illustration of the supramolecular architecture of the three major classes of prokaryotic cell envelopes containing crystalline bacterial cell surtece layers (S-layers). (a) Cell envelope structure of Gram-negative archaea with S-layers as the only cell wall component external to the cytoplasmic membrane, (b) Cell envelope as observed in Gram-positive archaea and bacteria. In bacteria the rigid wall component is primarily composed of peptidoglycan. In archaea other wall polymers (e.g., pseudomurein or methanochondroitin) are found, (c) Cell envelope profile of Gram-negative bacteria, composed of a thin peptidoglycan layer and an outer membrane. If present the S-layer is closely associated with the lipopolysaccharide of the outer membrane. (Modified after U.B. Sleytr, P. Messner, D. Pum, and M. Sdra. Crystalline Bacterial Cell Surface Proteins. Austin, TX R.G. Landes/Academic Press, 1996. With permission.)...

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