Relationship between Cell Wall, Cytoplasmic Membrane, and Bacterial Motility

High-resolution electron microscopy of polarly flagellated bacteria revealed that their flagella originate at a circular, differentiated portion of the cytoplasmic membrane approximately 25 nm in diameter. The flagella also have discs attaching them to the cell wall. These attachment discs are extremely resistant to lytic damage and are firmly bound to the flagella. The cytoplasm beneath the flagellum contains a granulated basal body about 60 nm in diameter, and a specialized polar membrane. The existence of membrane-bound basal bodies is shown to be an artifact arising from adherence of cell wall and cytoplasmic membrane fragments to flagella in lysed preparations. Based on structures observed, a mechanism to explain bacterial flagellar movement is proposed. Flagella are considered to be anchored to the cell wall and activated by displacement of underlying cytoplasmic membrane to which they are also firmly attached. An explanation for the membrane displacement is given.