Bacterial flagellum

A rotary protein appendage that propels many bacteria through liquid. Its filament is driven by a membrane-embedded motor powered mainly by ion flow.

Flagellar motor: A membrane-embedded molecular machine that rotates a bacterial flagellum. It converts ion flow across the membrane into the flagellum’s rotation.
Bacterial cell envelope: The layered boundary surrounding a bacterial cell, including its membranes and often a cell wall. The motor spans envelope layers to anchor and drive the external filament.
Bacterial motility: The capacity of bacteria to move actively, often using flagella or other cellular structures. Flagellar rotation is one major mechanism of bacterial locomotion.
Archaeal archaellum: A rotating surface filament that propels many archaea and is assembled by a type IV pilus-like system. It resembles a bacterial flagellum in function but differs in structure and assembly.
Bacterial chemotaxis: The process by which bacteria bias movement in response to chemical gradients. Chemotaxis changes motor rotation to steer swimming toward favorable conditions.
Basal body: The ringed, membrane-associated base of a bacterial flagellum that anchors the motor. Its rings and rods support rotation through the cell envelope.
Swarming motility: Coordinated surface movement by groups of bacteria, often involving flagella. Some bacteria use flagella to spread collectively across moist surfaces.
Eukaryotic flagellum: A motile cellular appendage built from microtubules and driven by dynein motors. It bends through motor-driven microtubule sliding rather than rotating as a rigid filament.
Proton motive force: An electrochemical gradient of protons across a membrane that can power cellular work. Many bacterial flagellar motors draw their energy from this gradient.
Flagellar type III secretion system: A specialized export apparatus that transports flagellar proteins through the growing structure. It delivers components to the distal end, where the filament extends.

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