Title: Enhanced bacterial swimming speeds in macromolecular polymer solutions,
Abstract: The locomotion of swimming bacteria in simple Newtonian fluids can
successfully be described within the framework of low Reynolds number
hydrodynamics. The presence of polymers in biofluids generally increases the
viscosity, which is expected to lead to slower swimming for a constant
bacterial motor torque. Surprisingly, however, several experiments have shown
that bacterial speeds increase in polymeric fluids, and there is no clear
understanding why. Therefore we perform extensive coarse-grained simulations of
a bacterium swimming in explicitly modeled solutions of macromolecular polymers
of different lengths and densities. We observe an increase of up to 60% in
swimming speed with polymer density and demonstrate that this is due to a
depletion of polymers in the vicinity of the bacterium leading to an effective
slip. However this in itself cannot predict the large increase in swimming
velocity: coupling to the chirality of the bacterial flagellum is also
necessary.