Bacteria swimming in a wall-bounded shear flow studied with microfluidic-DHM

Observations of bacterial motility in a wall-bounded shear flow are crucial to understand cell attachment at the onset of biofilm formation. We combined microfluidics and holography to measure 3-D trajectories of \textit{Escherichia coli }in shear flows, for shear rates up to 200/s. Acquisition of $>$3,000 trajectories over short times (5 min) enabled the robust quantification of swimming velocities and dispersion coefficients. We find that near-wall hydrodynamic interactions, including swimming in circles and the reduction in tumbling frequency, reduce the wall-normal dispersion of bacteria, favoring surface attachment. Preliminary results on the effect of shear will also be discussed.