Flagellated bacterial motility in polymer solutions

Abstract

It is widely believed that the swimming speed, $v$, of many flagellated bacteria is a non-monotonic 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 new, high-throughput methods for characterising motility, we have measured $v$, and the angular frequency of cell-body rotation, $\Omega$, of motile Escherichia coli as a function of polymer concentration in polyvinylpyrrolidone (PVP) and Ficoll solutions of different molecular weights. We find that non-monotonic $v(c)$ curves are typically due to low-molecular weight impurities. After purification by dialysis, the measured $v(c)$ and $\Omega (c)$ 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.

17 pages

References in corpus (5)

• The hydrodynamics of swimming microorganisms
• Propulsion in a viscoelastic fluid
• Differential Dynamic Microscopy of Bacterial Motility
• Theory of swimming filaments in viscoelastic media
• Differential Dynamic Microscopy: a High-Throughput Method for Characterizing the Motility of Microorganism

Cited by in corpus (14)

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• Intermediate scattering function of an anisotropic active Brownian particle
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• Helical propulsion in shear-thinning fluids
• Differential dynamic microscopy for the characterization of polymer systems
• Effects of shear thinning viscosity and viscoelastic stresses on flagellated bacteria motility
• The mechanism of propulsion of a model microswimmer in a viscoelastic fluid next to a solid boundary
• Random motion of a circle microswimmer in a random environment
• Dark Field Differential Dynamic Microscopy enables the accurate characterization of the roto-translational dynamics of bacteria and colloidal clusters
• Viscous propulsion in active transversely-isotropic media
• Biopolymer dynamics driven by helical flagella
• Escherichia coli as a model active colloid: a practical introduction
• Microswimming in viscoelastic fluids
• Helical trajectories of swimming cells with a flexible flagellar hook