Swimming bacteria in Poiseuille flow: The quest for active Bretherton-Jeffery trajectories

Using a 3D Lagrangian tracking technique, we determine experimentally the trajectories of non-tumbling E. coli mutants swimming in a Poiseuille flow. We identify a typology of trajectories in agreement with a kinematic active Bretherton-Jeffery model, featuring an axisymmetric self-propelled ellipsoid. In particular, we recover the swinging and shear tumbling kinematics predicted theoretically by Zottl and Stark (Phys. Rev. Lett., 108 (2012) 218104). Moreover using this model, we derive analytically new features such as quasi-planar piecewise trajectories, associated with the high aspect ratio of the bacteria, as well as the existence of a drift angle around which bacteria perform closed cyclic trajectories. However, the agreement between the model predictions and the experimental results remains local in time, due to the presence of Brownian rotational noise. Copyright (C) EPLA, 2019