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BP: Fachverband Biologische Physik

BP 6: Statistical Physics of Biological Systems II (joint DY, BP)

BP 6.1: Topical Talk

Monday, March 14, 2011, 14:00–14:30, HÜL 186

Collective dynamics in the cytoskeleton and swimming bacteria — •Falko Ziebert^1,2, Sumanth Swaminathan³, Shawn Ryan^4,5, Leonid Berlyand⁴, and Igor Aranson⁵ — ¹PCT - UMR CNRS Gulliver 7083, ESPCI, Paris, France — ²Physikalisches Institut, Universität Freiburg — ³Engineering Sciences and Applied Mathematics, Northwestern University, Evanston, U.S. — ⁴Department of Mathematics, Pennsylvania State University, U.S. — ⁵Materials Science Division, Argonne National Laboratory, Argonne, U.S.

Collective dynamics in active biological materials has attracted much attention in recent years. I will focus on select topics on two systems: i) semi-dilute cytoskeletal solutions where molecular motors induce self-organization of filaments and ii) collective swimming of bacteria solutions. In the first system I propose a model for the semi-dilute case, i.e. the regime of multi-filament interactions. I discuss the order of the isotropic-polar nematic transition - which can not be determined by macroscopic models - as well as the influence of motor fluctuations on the ordering and the respective defect patterns that form. In case of bacterial solutions, recent experimental studies evidenced a decrease in viscosity as a function of density/volume fraction of swimmers in case of pushers (e.g. B. subtilis). In contrast, pullers (e.g. chlamydomonas) lead to an increase in viscosity. To rationalize these findings we performed simulations and analytical work, demonstrating that the viscosity reduction in case of pushers is related to the onset of large-scale collective motion due to interactions between swimmers.