Flow-controlled densification of E. coli through a constriction

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

La Havana

Congreso; MarchCOMeeting?12. Complex matter physics: materials, dynamics and patterns.; 2012

The dynamics of bacterial suspensions flowing in confined spaces is relevant to understand their behavior in scenarios such as porous materials, soil, microbiology, water purification, and biomedical research. We show a new phenomenon concerning E. Coli suspensions flowing through a funnel-like constrictions in micro-fluidic channels. The applied flow induces a counter-intuitive symmetry breaking in the bacteria concentration, which is found to increase past the funnel. The concentration enhancement persists over large distances and its amplitude increases linearly with the flow rate and disappears at large flow values. We show that the effect is reversible when the flow direction is reversed. We explain the observed effects on the interactions between the active bacteria and the channel boundaries. As we know that solid boundaries may act as traps for the bacterial motion and may change drastically the transport properties of the suspension. We map our results onto a one dimensional convection/diffusion equation introducing a source term representing a long range non-local effect due to the presence of the central constriction. Our experiment opens the possibility to control the concentration bacterial suspensions in microfluidic channels by simply tuning the flow of liquid.