capsules and slime layers
Many prokaryotic cell are coverd with polysaccharides. In some cases the polymers are tightly integrated with the cell while in others they are loosely associated.The former is called a capsule,and the latter a slime layer (Figure2.2). Slime layer materials can diffuse into the medium with their structure and composition being dependent on growth conditions. An important role for these structures is adhesion to host cell for invasion or to a solid surface to initiate and stabilize biofilm formation. These structures are also responsible for resistance to phagocytosis,thereby increasing virulence. In some bacteria the capsule functions as a receptor for phage.Since the polysaccharides are hydrophilic, they can also protect cells from desiccation.
2.3.3 S-layer,outer membrane and cell wall
Unicellular prokaryotes have elaborate surface structures. These include the S-layer, outer membrane and cell wall. The cell wall determines the physical shape of prokaryotic cells in most cases. Prokaryotes can be classified into four groups according to their cell wall structure. theas are mycoplasmas,Gram-nagative bacteria,gram-positive bacteria and archaea.cell walls are not foundbin mycoplasmas which are obligate intrecellular pathogens. M