FINE-STRUCTURE OF S-LAYERS

S-layers are now considered a common cell wall structure in Bacteria a nd Archaea as well as in some algae. Morphological and chemical studie s have revealed that S-layers consist of crystalline arrays of protein or glycoprotein subunits forming oblique, square or hexagonal lattice s on the cell surface, Electron microscopy and computer image enhancem ent techniques have been applied to obtain structural information down to the nanometer range. This chapter deals with the wide distribution of S-layers among cyanobacteria, and their morphological and chemical characterization, and the potential of high resolution electron micro scopic studies applied to the cell envelope of Pyrodictium. The occurr ence of S-layers in cyanobacteria was investigated by cryomethods and ultrathin sectioning. These investigations indicate that the ultrastru cture of S-layers may be exploited as an auxiliary taxonomic criterion in the classification of cyanobacteria. Pyrodictium is the first orga nism which has shown an optimum growth temperature above 100 degrees C . The highly irregularly shaped, flagellated cells are interconnected by extracellular tubules, The three-dimensional structure of this netw ork was visualized with high resolution scanning electron microscopy w hile the fine structure of the cell wall architecture was studied in d etail with Various electron microscopic techniques, Both contributions demonstrate that the investigation of the fine structure of S-layers is fundamental for establishing structure-function relationships for t hese two-dimensional crystalline arrays.