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Applied Mathematics Colloquium

Friday, April 11, 11:30 am
Cullimore Lecture Hall II
New Jersey Institute of Technology

Onset of Collective Behavior in Colonies of Swimming Microorganisms

Igor Aronson

Materials Science Division

Argonne National Laboratory

Argonne, IL

Abstract

At concentrations near the maximum allowed by steric repulsion, swimming bacteria form a dynamical state exhibiting extended spatio-temporal coherence. The viscous fluid into which locomotive energy of individual microorganisms is transferred also carries interactions that drive the coherence. The concentration dependence of correlations in the collective state is probed here with a novel technique that herds bacteria into condensed populations of adjustable concentration. Continuum models have indicated that a state of uniform swimming order is linearly unstable at finite wavelengths, but have not addressed the nonlinear dynamics of the coherent state, with its biological implications for mixing, transport, and intercellular communication. We investigate a specific model incorporating hydrodynamic interactions in thin-film geometries and show by numerical studies that it displays large scale persistently recurring vortices, as actually observed.