A membrane-associated conveyor belt controls the rotational direction of the bacterial type 9 secretion system.

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Many bacteria utilize the type 9 secretion system (T9SS) for gliding motility, surface colonization, and pathogenesis. This dual-function motor supports both gliding motility and protein secretion, where rotation of the T9SS plays a central role. Fueled by the energy of the stored proton motive force and transmitted through the torque of membrane-anchored stator units, the rotary T9SS propels an adhesin-coated conveyor belt along the bacterial outer membrane like a molecular snowmobile, thereby enabling gliding motion. However, the mechanisms controlling the rotational direction and gliding motility of T9SS remain elusive. Shedding light on this mechanism, we find that in the gliding bacterium Flavobacterium johnsoniae , deletion of the C-terminus of a conveyor belt protein controls, and in fact, reverses the rotational direction of T9SS from counterclockwise (CCW) to clockwise (CW). Largescale conformational changes at the interface of the T9SS ring with the C-terminus of the conveyer belt, as well as those of the ring protein themselves, in concert with a CW bias of the stators general rotation brings forth a 'tri-component gearset' model: the conveyor belt controls the conformation of the T9SS ring, and thereby its rotational direction. Consequently, the CW rotating stator either push the outer edge of the T9SS rings, causing its CCW rotation or press against the inner surface of the rings, resulting in CW rotation. This regulatory mechanism exemplifies how an outer membrane associated conveyor belt adjusts the rotational direction of its driver, the T9SS, thus providing adaptive sensory feedback to control the motility of a molecular snowmobile.