• Open Access

Evaporation-driven convective flows in suspensions of nonmotile bacteria

Jocelyn Dunstan, Kyoung J. Lee, Yongyun Hwang, Simon F. Park, and Raymond E. Goldstein
Phys. Rev. Fluids 3, 123102 – Published 28 December 2018
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Abstract

We report a novel form of convection in suspensions of the bioluminescent marine bacterium Photobacterium phosphoreum. Suspensions of these bacteria placed in a chamber open to the air create persistent luminescent plumes most easily visible when observed in the dark. These flows are strikingly similar to the classical bioconvection pattern of aerotactic swimming bacteria, which create an unstable stratification by swimming upwards to an air-water interface, but they are a puzzle since the strain of P. phosphoreum used does not express flagella and therefore cannot swim. When microspheres were used instead of bacteria, similar flow patterns were observed, suggesting that the convective motion was not driven by bacteria but instead by the accumulation of salt at the air-water interface due to evaporation of the culture medium. Even at room temperature and humidity, and physiologically relevant salt concentrations, the water evaporation was found to be sufficient to drive convection patterns. To prove this hypothesis, experiments were complemented with a mathematical model that aimed to understand the mechanism of plume formation and the role of salt in triggering the instability. The simplified system of evaporating salty water was first studied using linear stability analysis, and then with finite element simulations. A comparison between these three approaches is presented. While evaporation-driven convection has not been discussed extensively in the context of biological systems, these results suggest that the phenomenon may be broadly relevant, particularly in those systems involving microorganisms of limited motility.

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  • Received 7 April 2017

DOI:https://doi.org/10.1103/PhysRevFluids.3.123102

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

Published by the American Physical Society

Physics Subject Headings (PhySH)

Physics of Living SystemsFluid Dynamics

Authors & Affiliations

Jocelyn Dunstan1,*, Kyoung J. Lee2, Yongyun Hwang3, Simon F. Park4, and Raymond E. Goldstein1,†

  • 1Department of Applied Mathematics and Theoretical Physics, Centre for Mathematical Sciences, University of Cambridge, Cambridge CB3 0WA, United Kingdom
  • 2Department of Physics, Korea University, Seoul, Korea
  • 3Department of Aeronautics, Imperial College, London, United Kingdom
  • 4Faculty of Health & Medical Sciences, University of Surrey, Guildford GU2 5XH, Surrey, United Kingdom

  • *Present address: Institute of Biomedical Sciences (ICBM), Faculty of Medicine / Center for Mathematical Modeling (CMM), Faculty of Physical and Mathematical Sciences, Universidad de Chile, Santiago, Chile.
  • Corresponding author: R.E.Goldstein@damtp.cam.ac.uk

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Vol. 3, Iss. 12 — December 2018

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