Crystalline surface layers (S-layers) represent an almost universal feature of archaebacterial cell envelopes and can be found in gram-positive and gram-negative eubacterial species from nearly all phylogenetic branches. S-layers consist of a single protein- or glycoprotein species and thus can be considered as one of the most primitive membrane structures developed during evolution. Prokaryotes carrying S-layers are ubiquitously found in every part of the biosphere. This supports the concept of a general supramolecular "porous crystalline surface layer" fulfilling a broad spectrum of functions which are strongly dependent on the particular environmental and ecological conditions. Their structural simplicity makes S-layers a suitable model for analyzing structure-function relationships as well as dynamic aspects of membrane morphogenesis.

Table of Contents:
Comparative Chemistry of the Rigid Cell Wall Component and its Phylogenetic Implications.- Comparative Aspects on Archaeobacterial Proteinaceous Cell Envelopes.- Evidence for the Glycoprotein Nature of Eubacterial S-Layers.- The Surface Layers of Lampropedia hyalina.- A Glycoprotein Surface Layer Covers the Pseudomurein Sacculus of the Extreme Thermophile Methanothermus fervidus.- The Structure, Chemistry and Physicochemistry of the Methanospirillum hungatei GP1 Sheath.- Ultrastructural and Biochemical Studies of the Cell Sheath of Methanothrix soehngenii.- The S-Layers of Aquaspirillum serpens.- Image Analysis of the Two Patterns from Negatively Stained A-Layers of Aeromonas salmonicida: Correction for Lattice Distortions.- The A-Layer of Aeromonas salmonicida: Organization and Functions.- Thermoresistance of A-Layer-Deficient Mutants of Aeromonas salmonicida.- The S-Layer of Pathogenic Strains of Aeromonas hydrophila.- The Three-Dimensional Structure of Bacterial Surface Layers.- Characterization of the Surface Protein of Comamonas acidovorans.- The Surface Protein of the Archaebacterium Thermoproteus tenax.- The Structure of Surface Proteins in Sulfolobus.- Structure of the Surface Glycoprotein from Halobacterium volcanii as Revealed by Electron Microscopy.- The Structure of the Surface Protein of Thermotoga maritima.- Three-Dimensional Structure of Surface Layers from Various Bacillus and Clostridium Species.- Paracrystalline Surface Layer of a Novel Bacillus sp M3198.- Three-Dimensional Structure of the Regular Tetragonal Surface Layer of Azotobacter vinelandii.- Structure and Assembly of the Oblique S-Layer Lattice of Bacillus stearothermophilus Strain NRS 2004/3a.- Charge Distribution of S-Layers and Importance of Charged Groups for Morphogenesis and Function.- Localized Insertion of New S-Layer During Growth of Bacillus stearothermophilus Strain PV72.- Crystalline Surface Layers in Anaerobic Bacteria Isolated from a Patient with Secretory Otitis Media and a Draining Ear.- Occurrence and Characterization of S-Layers in Oral Bacteria.- Ultrastructural Comparison of Bacteroides heparinolyticus and Bacteroides buccae.- S-Layers in Cyanobacteria.- Cloning and Sequencing of the S-Layer Glycoprotein Gene of Halobacterium halobium.- The Primary Structure of the HPI-Layer Polypeptide of Deinococcus radiodurans.- Characterization and Application of S-Layer Protein Gene for Production of Foreign Proteins in a Protein-Producing Bacillus brevis 47.- Permebility Properties and the Use of S-Layers for the Production of Ultrafiltration Membranes.- Comparative Studies on Synthetic and S-Layer Ultrafiltration Membranes.- Appendix Crystalline Surface Layers on Bacteria.- References.