(155f) Reduced Viscosity Experienced By Flagella Moving in a Solution of Long Polymer Chains

Human and animal infections are mostly caused by bacteria and motility is important in their response to cues and colonization. Bacteria usually swim by rotating their helical flagella attached to the cell body. The natural inhabitant of bacteria usually exhibits a non-Newtonian behavior due to the presence of polymer molecules, proteins or other micro structures. Experiments have found that bacteria can swim faster in a polymer solution when the polymer molecules have a high molecular weight. The thickness of the flagellum (~20 nm) can be smaller than the size of the polymer molecules and the continuum models for polymer solutions are not appropriate for this problem. In this work, we overcome the limit of the continuum models by modeling the polymer molecules using a Brownian Dynamics method. A large number of polymer molecules are embedded in a Newtonian solvent, where the polymer molecules are modeled as bead-spring dumbbells. Our Brownian Dynamics results illustrate that the hydrodynamic torque acting on the flagellum decreases as the polymer size increases. As a result, the flagellum experiences smaller microscopic viscosity than the apparent viscosity of the polymer solution.