Rheotaxis of E. coli in Complex Fluids

The positive rheotaxis of microorganisms in Newtonian fluids encompasses the spontaneous orientation of individual swimmers against a unidirectional flow. This mechanism is now understood as being governed mainly by the positioning of the swimmer at an angle in the high shear flow region close to solid boundaries. Further studies underline a similar behavior for artificial self-propelled swimmers and demonstrates the hydrodynamic interplays that prescribes the swimmer’s gait.

 

Microorganisms have evolved to thrive in fluids that exhibit non-Newtonian behavior; these complex fluids are ubiquitous in nature and particularly in the human body. Our study focuses on the description of E. coli’s rheotaxis in different dilute polymer solutions. Experiments show that the flux upstream is increased by an order of magnitude in viscoelastic shear-thinning fluids as opposed to strictly Newtonian viscous fluids. The analysis of E. coli orientation distribution allows us to quantify the relative contribution of the elastic and viscous stresses on the phenomena.