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

Abstract

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 GldJ controls, and in fact, reverses the rotational direction of T9SS from counterclockwise to clockwise thus suggesting that the interface between the conveyor belt protein GldJ and the T9SS ring protein GldK plays an important role in controlling the directionality of T9SS. Combined with MD simulation of the T9SS stator units GldLM, we suggest a 'tri-component gearset' model where the conveyor belt controls the rotational direction of its driver, the T9SS, thus providing adaptive sensory feedback to influence the motility of the gliding bacterium.