Fig. 3: Sedimentation is necessary for the accumulation of non-motile bacteria that follow a recirculating backflow.
From: Active segregation in bacterial binary mixtures under flow
a Position of the center of mass of non-motile bacteria as a function of time with (ΔG = 1) and without (ΔG = 0, density-matched medium) sedimentation (ϕM = 0.51%, ϕNM = 1.7%, \(\dot{\gamma }=5.6\) s−1), with ΔG the non-motile sedimentation speed relative to its value in motility buffer. b,c Drift of motile and non-motile cells at increasing distances z from the bottom surface, along (b) and perpendicular (c) to the direction of the main flow, with and without sedimentation, away from the side walls of the channel (ϕM = 0.51%, ϕNM = 1.7%, \(\dot{\gamma }=5.6\) s−1). Vertical error bars represent the standard deviation (SD) over n = 3 biological replicates, horizontal error bars represent the depth of field (4 μm) of the fluorescence microscope. The drift is measured via φDM image velocimetry, except for non-motile cells at z > 35 μm, where particle tracking was used to increase measurement precision (Methods). d Scheme of the accumulation mechanism. Perpendicular to the main flow, motile cells perform chirality-induced rheotaxis (red arrows), resulting in a recirculating, conveyor-belt-like, backflow that advects non-motile cells (blue arrows). Accumulation happens only in the presence of sedimentation (right).
