Dresden 2009 – scientific programme

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BP: Fachverband Biologische Physik

BP 17: Poster II

BP 17.33: Poster

Wednesday, March 25, 2009, 17:15–19:45, P3

Formation of Domains in Bacterial Flagella — •Reinhard Vogel and Holger Stark — TU Berlin

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

In general, the helical shape of the bacterial flagellum can assume 11 different configurations depending, e.g., on mechanical loading, temperature, and chemical composition of the solution. In recent optical tweezer experiments, Darnton and Berg [1] pulled at the flagellum and induced transformations between different helical configurations but they also observed the simultaneous occurence of two configurations separated by a transition region. We investigate this domain formation by extending the linear elasticity theory of thin helical rods. We compare two types of elastic free energy with two stable helical states. One is a polynomial of degree four, the other a composition of two harmonic potentials. For realistic parameter values, we discuss the force extension curve for both free energies as a function of pulling speed and explore the influence of thermal noise. Especially for the second free energy, the force extension curve exhibits sharp transitions between two helical configurations reminiscent to experiments.

[1] N.C.Darnton H.C. Berg, Biophys. J. 92, 2230-2236 (2007)