Dresden 2011 – scientific programme

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BP: Fachverband Biologische Physik

BP 1: Statistical Physics in Biological Systems I (joint DY, BP)

BP 1.2: Talk

Monday, March 14, 2011, 10:45–11:00, ZEU 250

The flow field of an individual bacterium and its implications for cell-cell and cell-surface interactions — Knut Drescher¹, •Jörn Dunkel¹, Luis Cisneros², Sujoy Ganguly¹, and Raymond Goldstein¹ — ¹DAMTP, University of Cambridge, Wilberforce Road, Cambridge CB3 0WA, UK — ²Department of Physics, University of Arizona, 1118 E 4th St, Tucson, AZ 85721, USA

Swimming bacteria create microflows that have been commonly assumed to play an important role in their pair-interactions and during scattering with surfaces. Here, we present the first direct measurement of the bacterial flow field generated by individual E. coli. Our experiments allow us to infer the relative importance of fluid dynamics and noise for cell-cell and cell-surface scattering. We find that rotational diffusion due to thermal and intrinsic stochasticity drowns the effects of long-range hydrodynamic pair-interactions, implying that physical interactions between bacteria are dominated by steric collisions and near-field lubrication forces. This closely links collective motion in bacterial suspensions to self-organization in driven granular systems, assemblages of biofilaments, and animal flocks. We further conclude that long-range fluid dynamics is negligible for the scattering of bacteria with surfaces. However, once a bacterium has aligned with the surface through an inelastic collision and swims along the surface at a distance of less than two microns, the self-generated flow traps the bacterium and large fluctuations in orientation are needed to escape. Since our results are based on purely mechanical properties, they are expected to apply to a wide range of bacteria.