Berlin 2012 – scientific programme

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BP: Fachverband Biologische Physik

BP 11: Focus: Statistics of Cellular Motion (with DY)

BP 11.9: Talk

Tuesday, March 27, 2012, 12:45–13:00, H 1028

Rotationally induced polymorphic transitions of a bacterial flagellum — A full model of swimming Rhodobacter sphaeroides — •Reinhard Vogel and Holger Stark — Institute of Theoretical Physics, TU Berlin

The bacterium Rhodobacter sphaeroides swims by rotating a helical filament also called flagellum. The filament is driven by a rotary motor. Depending on the speed of the motor, the flagellum assumes different configurations characterized by its pitch and radius (polymorphism). If the motor stops, the flagellum relaxes into a coiled form with large radius and small pitch, whereas if the motor runs it assumes a helical state with large pitch better suited for swimming. Due to the switch between running and stopping, the bacterium changes its direction randomly.

The bacterial flagellum consists of three parts; the rotary motor embedded in the cell membrane, a short proximal hook that acts as a universal joint and 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 a bacterium forward. We present our approach to mimic the rotary motor and hook within a continuum model of the flagellum. We use the elastic theory for flagellar polymorphism, developed in Ref. [1], to investigate how an applied motor torque induces a transition between two polymorphic configurations. We attach the bacterial flagellum to a load particle and thereby model the locomotion of the bacterium Rhodobacter sphaeroides.

[1] R. Vogel and H. Stark, Eur. Phys. J. E 33, 259–271 (2010).