H. P. Zhang et al 2009 EPL 87 48011 doi:10.1209/0295-5075/87/48011
H. P. Zhang, Avraham Be'er, Rachel S. Smith, E.-L. Florin and Harry L. Swinney
Show affiliationsWe determine and relate the characteristic velocity, length, and time scales for bacterial motion in swarming colonies of Paenibacillus dendritiformis growing on semi-solid agar substrates. The bacteria swim within a thin fluid layer, and they form long-lived jets and vortices. These coherent structures lead to anisotropy in velocity spatial correlations and to a two-step relaxation in velocity temporal correlations. The mean squared displacement of passive tracers exhibits a short-time regime with nearly ballistic transport and a diffusive long-time regime. We find that various definitions of the correlation length all lead to length scales that are, surprisingly, essentially independent of the mean bacterial speed, while the correlation time is linearly proportional to the ratio of the correlation length to the mean speed.
47.63.Gd Swimming microorganisms
87.18.Gh Cell-cell communication; collective behavior of motile cells
Issue 4 (August 2009)
Received 17 July 2009, accepted for publication 14 August 2009
Published 15 September 2009
H. P. Zhang et al 2009 EPL 87 48011
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