Bacteria that glide with helical tracks

Abstract

Many bacteria glide smoothly on surfaces, despite having no discernable propulsive organelles on their surface. Recent experiments with Myxococcus xanthus and Flavobacterium johnsoniae show that both of these distantly related bacterial species glide using proteins that move in helical tracks, albeit with significantly different motility mechanisms. Both species utilize proton-motive force for movement. Although the motors that power gliding in M. xanthus have been identified, the F. johnsoniae motors remain to be discovered.

Figure 1

The helical rotor mechanism in M. xanthus. A schematic of the endless helical protein track on which the motors (large circles) walk. The thick lines show the leftward motion of the motors that drive the rightward direction of gliding. The thin red lines show the fewer number of rightward moving motors on the opposite strand. The model shows that the motors slow down in the ventral ‘traffic jam’ where they encounter the high drag region. The higher resolution inset shows the motors walking on the cytoplasmic track carrying large ‘cargo’ of motor associated proteins that deform the cell wall. The deformation pushes on the external slime providing the thrust that drives the cell gliding.

Figure 2

Speculative model for movement of F. johnsoniae cell-surface adhesins. A) The surface adhesins move along a looped helical track. B) A portion of the cell envelope is shown. The motors, anchored to the peptidogly can, harvest the proton gradient across the inner membrane. A portion of the motor complex extends through the peptidogly can layer and interacts with an outer membrane associated protein (baseplate) that carries the cell surface adhesins. Repeated movements of this portion of the motor propels the base plate and attached adhesins along the cell surface until they are engaged by the next motor.