Self-organization of E. coli suspensions in confined flows

G L. MIÑO; E ALTSHULER; J GACHELIN; C. PÉREZ-PENICHET,; L. DEL RÍO; A. LINDNER,; A. ROUSSELET; E. CLÉMENT

París

Simposio; FPGG Spring Symposium; 2011

Fondation Pierre-Gilles de Gennes

In this work, we studied the dynamics of bacterial suspensions flowing in micro-fluidic device with different geometries. We worked with wild type E.Coli suspensions submitted to various shear flow in order to stimulate a collective response of the bacteria to the hydrodynamic stress. When an E. Coli suspension was injected through a funnel-like constriction, we observed an accumulation of bacteria after the constriction. Bacteria swimming trajectories obtained after tracking revealed that these bacteria swam up-flow. This accumulation increases with flow velocity up to a maximum value and disappears at high flux values. This was not observed with a suspension of dead bacteria. Thus, as expected, using this approach we evidenced the induction of bacteria collective organization induced by a shear flow.In a second set of experiments, we used a Y shaped channel to characterize the viscosity of a fluid activated by Bacteria. We injected at the same flow rate in one of the input branch an active suspension of E.Coli, and an identical fluid that did not contain bacteria in the other branch. Both suspensions meet at the junction point and flow in the output branch showing a fuzzy interface. This device can be seen as a rheometer as the position of the interface is directly related to the viscosity ratio between the two fluids. We systematically measured the position of this separation line using either beads in suspension, dead and active bacteria in order to measure the effective viscosities of the suspensions.