(234b) Dynamics and Rheology of Magnetotactic Bacterial Suspensions

Zhengyang Liu, Kechun Zhang, and Xiang Cheng

Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN 55455, USA

Bacterial suspensions, a premier example of active fluids, have unique rheological properties different from that of passive colloidal suspensions. Although the reduction of the viscosity of bacterial suspensions and the existence of bacterial “superfluids” have been demonstrated in macroscopic rheology measurements, few experiments have been conducted to reveal the influence of the microscopic dynamics of individual bacteria on the bulk rheology of bacterial suspensions. Here, using a magnetotactic bacterial strain and a microfluidic viscometer, we show that the viscosity of bacterial suspensions can be actively controlled via external magnetic fields. By varying the orientation and the persistent motion of individual bacteria through the magnetic fields, we distinguish the relative contribution of hydrodynamic and swimming stresses on the rheology of bacterial suspensions. Our study reveals the microscopic origin of the unusual flow behaviors of bacterial suspensions and demonstrates a new type of magnetorheological fluids.