The locomotion of swimming bacteria in simple Newtonian fluids can successfully be described within the framework of low-Reynolds-number hydrodynamics1. 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, experiments have shown that bacterial speeds can increase in polymeric fluids2–5. Whereas, for example, artificial helical microswimmers in shear-thinning fluids6 or swimming Caenorhabditis elegans worms in wet granular media7,8 increase their speeds substantially, swimming Escherichia coli bacteria in polymeric fluids show just a small increase in speed at low polymer concentrations, followed by a decrease at higher concentrations2,4. The mechanisms behind this behaviour are currently unclear, and therefore we perform extensive coarse-grained simulations of a bacterium swimming in explicitly modelled 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 non-uniform distribution of polymers in the vicinity of the bacterium, leading to an apparent slip. However, this in itself cannot predict the large increase in swimming velocity: coupling to the chirality of the bacterial flagellum is also necessary.Bacteria and other helical microswimmers are known to swim faster in non-Newtonian fluids. Coarse-grained simulations suggest the increase may be due to a polymer depletion effect near the body and flagellum, inducing a slip velocity at the surface.
Enhanced bacterial swimming speeds in macromolecular polymer solutions
Published 2017 in Nature Physics
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- Publication year
2017
- Venue
Nature Physics
- Publication date
2017-10-10
- Fields of study
Biology, Materials Science, Physics
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