Fig. 2: The rheotactic flux of motile cells induces the non-motile cell advection in the opposite direction.

a,b Position of the center of mass of non-motile cells as a function of time (a) for different motile volume fractions ϕ_M, at fixed non-motile volume fraction ϕ_NM = 1.7% and shear rate \(\dot{\gamma }\) = 5.6 s⁻¹, and (b) for increasing applied shear rates, at fixed ϕ_M = 0.17% and ϕ_NM = 1.7%. Solid lines are linear (ϕ_M ≤ 0.051%) or saturated exponential fits. c Drift velocity of the non-motile center of mass, obtained as the initial slope of the fitting curves of a. The dashed line represents a linear fit for non-tumbling data for ϕ_M ≤ 0.17% (slope = 0.96 μm.s⁻¹.%⁻¹). d Drift velocities of non-motile cells \({v}_{y}^{NM}\), extracted from b, and the rheotactic velocity of motile cells \({v}_{y}^{M}\), measured with particle tracking at 2.6 μm from the bottom surface (ϕ_M = 0.17%, ϕ_NM = 1.7%), as a function of shear rate. Positive y-direction is defined in Fig. 1b. The dashed horizontal line marks v = 0. e Relation between the drift of non-motile cells and the rheotactic flux of the motile cells \({\phi }_{M}{v}_{y}^{M}\). The dashed line represents a linear fit of all the points, with a slope of 20.4. a–e Error bars represent the standard deviation (SD) over n = 3 biological replicates. Each biological replicate is the average of four positions through the channel. f Schematics of the putative mechanism driving particle accumulation under shear.