title: Flagellated bacterial motility in polymer solutions.
abstract: It is widely believed that the swimming speed, v, of many flagellated bacteria is a nonmonotonic function of the concentration, c, of high-molecular-weight linear polymers in aqueous solution, showing peaked v(c) curves. Pores in the polymer solution were suggested as the explanation. Quantifying this picture led to a theory that predicted peaked v(c) curves. Using high-throughput methods for characterizing motility, we measured v and the angular frequency of cell body rotation, Ω, of motile Escherichia coli as a function of polymer concentration in polyvinylpyrrolidone (PVP) and Ficoll solutions of different molecular weights. We find that nonmonotonic v(c) curves are typically due to low-molecular-weight impurities. After purification by dialysis, the measured v(c) and Ω(c) relations for all but the highest-molecular-weight PVP can be described in detail by Newtonian hydrodynamics. There is clear evidence for non-Newtonian effects in the highest-molecular-weight PVP solution. Calculations suggest that this is due to the fast-rotating flagella seeing a lower viscosity than the cell body, so that flagella can be seen as nano-rheometers for probing the non-Newtonian behavior of high polymer solutions on a molecular scale.
authors.affiliation: Scottish Universities Physics Alliance (SUPA), School of Physics and Astronomy, University of Edinburgh, Edinburgh EH9 3FD, United Kingdom; vincent.martinez@ed.ac.uk.
authors.forename: Vincent A
authors.initials: VA
authors.lastname: Martinez
authors.affiliation: Scottish Universities Physics Alliance (SUPA), School of Physics and Astronomy, University of Edinburgh, Edinburgh EH9 3FD, United Kingdom;
authors.forename: Jana
authors.initials: J
authors.lastname: Schwarz-Linek
authors.affiliation: Scottish Universities Physics Alliance (SUPA), School of Physics and Astronomy, University of Edinburgh, Edinburgh EH9 3FD, United Kingdom;
authors.forename: Mathias
authors.initials: M
authors.lastname: Reufer
authors.affiliation: Department of Physics, University of York, York YO10 5DD, United Kingdom; and The Rowland Institute at Harvard, Cambridge, MA 02142.
authors.forename: Laurence G
authors.initials: LG
authors.lastname: Wilson
authors.affiliation: Scottish Universities Physics Alliance (SUPA), School of Physics and Astronomy, University of Edinburgh, Edinburgh EH9 3FD, United Kingdom;
authors.forename: Alexander N
authors.initials: AN
authors.lastname: Morozov
authors.affiliation: Scottish Universities Physics Alliance (SUPA), School of Physics and Astronomy, University of Edinburgh, Edinburgh EH9 3FD, United Kingdom;
authors.forename: Wilson C K
authors.initials: WC
authors.lastname: Poon
mesh_terms: D004926:Escherichia coli / Q000502:physiology*; D005362:Ficoll; D005407:Flagella / Q000502:physiology*; D057446:Hydrodynamics; D008954:Models, Biological; D009068:Movement; D011205:Povidone; D012212:Rheology; D014783:Viscosity
chemical_list: D005362:Ficoll; D011205:Povidone
keywords: complex fluids; non-Newtonian fluids; rheology; swimming microorganisms