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A. Zöttl, A. Mathijssen, N. Figueroa-Morales, G. Junot, E. Clement, A. Lindner:
"Oscillatory dynamics of swimming E. coli bacteria at walls in Poiseuille flow";
Talk: 71st Annual Meeting of the APS Division of Fluid Dynamics, Atlanta; 2018-11-18 - 2018-11-20.

Swimming microorganisms respond to flows in highly diverse and complex environments, at scales ranging from open oceans to narrow capillaries. The combined effects of fluid flow and boundaries lead to preferred swimmer orientation breaking the up/down-stream and left/right symmetry. To date, this so-called bacterial surface rheotaxis has been quantified by measuring instantaneous orientation distributions or average transport velocities, but a complete picture is still missing.

We investigate the time-resolved orientation dynamics of E.coli bacteria, theoretically and experimentally, as a function of applied shear close to walls. With increasing flow, we identify four regimes separated by critical shear rates: (I) circular swimming with a bias along the direction of vorticity; (II) upstream swimming without oscillations; (III) oscillatory motion, increasingly more to the left; (IV) coexistence of swimming to the left and to the right, with dynamical switching between these states. By modeling bacterial rheotaxis comprehensively - accounting for their chiral nature, hydrodynamic and steric interactions, elongation, fore-aft asymmetry and activity - we assess the relative importance of these contributions throughout a trajectory, and explain the full dynamics.

Project Head Gerhard Kahl:
DFS