Dresden 2011 – scientific programme

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BP: Fachverband Biologische Physik

BP 27: Physics of Cells III

BP 27.2: Talk

Thursday, March 17, 2011, 14:30–14:45, ZEU 250

Buckling instability of motor driven rotating bacterial flagella — •Reinhard Vogel and Holger Stark — TU Berlin

Many types of bacteria, such as E. coli and Salmonella, swim by rotating a bundle of helical filaments also called flagella. Each filament is driven by a rotary motor. When its sense of rotation is reversed, the flagellum leaves the bundle and undergoes a sequence of configurations characterized by their pitch, radius, and helicity (polymorphism). Finally the flagellum assumes its original form and returns into the bundle.

The bacterial flagellum consists of three parts; the rotary motor embedded in the cell membrane, a short proximal hook that couples the motor to the third part, the long helical filament. The helical shape of the filament converts rotational motion into a thrust force that pushes the bacteria forward.

In our contribution, we demonstrate how the hook, which transfers the motor torque to the filament, can be modeled. We then investigate how the flexible filament reacts on the applied motor torque. For small torques and a resulting thrust force pushing the bacterium forward, the helical axis is approximately parallel to the motor torque and the helical filament is only slightly compressed. However, when the torque is increased, the straight helical form becomes unstable and we observe a buckling instability or Hopf bifurcation when the compression becomes too strong. We analyze how the mobility of the cell body and thermal noise influence the instability and discuss its biological implications, in particular, for the formation of the bundle.