Deformations in the hook and flagellum during bacterial flick motility

Dynamical bending, buckling, and polymorphic transformations of the thin flagellar filament are known to affect bacterial motility in fluids. The run-reverse-flick motility of monotrichous bacteria also involves the even more flexible hook which connects the flagellum to its rotary motor. First, I will discuss the role of dynamic bending of both the hook and flagellum during the initiation of flicks. We obtain accurate estimates of forces and torques on the hook that suggest that flicks occur for stresses below the (static) Euler buckling criterion, then provide a mechanistic model for flick initiation that requires combined bending of the hook and flagellum. We calculate the triggering torque-stiffness ratio and find that our predicted onset of dynamic instability corresponds well with experimental observations. Second, I will discuss a more efficient numerical treatment of the dynamics of an inextensible filament that will allow modeling of the complete dynamics of the flick as well as recently discovered unconventional bacterial flagellar motility modes.