S-Layer

S-layer is a regularly structured layer that is found in many Gram positive and Gram negative bacteria. S-layers are present on the surface of the bacteria and in almost all archaea and they are composed of protein or glycoprotein. In Gram positive bacteria, it is associated with peptidoglycan; and in Gram negative bacteria, it is linked to the outer membrane. It maintains the shape and rigidity of bacterial cell and provides protection against osmotic stress, enzymes (for instance: lytic enzyme), ions and pH fluctuations and predacious bacteria like Bdellovibrio. It also provides adhesion property to the cell and helps them to attach to the surfaces. S-layer is responsible for the virulence of some pathogens by protecting them against phagocytosis and complement attack.