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Biophysical Characterization of Flagellar Motor Functions
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Flagellated bacterial motility in polymer solutions.

Vincent A Martinez1, Jana Schwarz-Linek2, Mathias Reufer2

  • 1Scottish Universities Physics Alliance (SUPA), School of Physics and Astronomy, University of Edinburgh, Edinburgh EH9 3FD, United Kingdom; vincent.martinez@ed.ac.uk.

Proceedings of the National Academy of Sciences of the United States of America
|December 4, 2014
PubMed
Summary

Bacterial swimming speed is not typically peaked by polymer solutions; impurities cause this effect. After purification, flagellar rotation reveals non-Newtonian fluid behavior in high-molecular-weight polymer solutions.

Keywords:
complex fluidsnon-Newtonian fluidsrheologyswimming microorganisms

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Area of Science:

  • Microbiology
  • Biophysics
  • Polymer Science

Background:

  • Flagellated bacteria motility is often described as a nonmonotonic function of polymer concentration, exhibiting peaked swimming speed curves.
  • This phenomenon was previously attributed to polymer solution pores, leading to theoretical predictions of peaked curves.

Purpose of the Study:

  • To investigate the factors influencing bacterial swimming speed in polymer solutions.
  • To clarify the role of impurities and polymer concentration on bacterial motility.
  • To explore the potential of flagella as nano-rheometers for probing non-Newtonian fluid dynamics.

Main Methods:

  • High-throughput methods were used to measure the swimming speed (v) and angular frequency of cell body rotation (Ω) of motile Escherichia coli.
  • Measurements were conducted across varying concentrations of polyvinylpyrrolidone (PVP) and Ficoll solutions with different molecular weights.
  • Bacterial samples were purified by dialysis to remove low-molecular-weight impurities.

Main Results:

  • Nonmonotonic swimming speed curves were predominantly attributed to low-molecular-weight impurities, not inherent polymer effects.
  • After purification, bacterial motility (v and Ω) generally followed Newtonian hydrodynamics, except for the highest molecular weight PVP.
  • Evidence of non-Newtonian behavior was observed in the highest molecular weight PVP solution.

Conclusions:

  • The perceived peaked swimming speed curves in flagellated bacteria are typically artifacts of impurities.
  • Purified bacterial motility in polymer solutions largely adheres to Newtonian hydrodynamics.
  • Bacterial flagella can serve as effective nano-rheometers to probe non-Newtonian properties of polymer solutions at a molecular scale.