Issue
EPL
Volume 87, Number 4, August 2009
Article Number 48011
Number of page(s) 5
Section Interdisciplinary Physics and Related Areas of Science and Technology
DOI http://dx.doi.org/10.1209/0295-5075/87/48011
Published online 15 September 2009
EPL, 87 (2009) 48011
DOI: 10.1209/0295-5075/87/48011

Swarming dynamics in bacterial colonies

H. P. Zhang, Avraham Be'er, Rachel S. Smith, E.-L. Florin and Harry L. Swinney

Center for Nonlinear Dynamics and Department of Physics, The University of Texas at Austin Austin, TX 78712, USA

zhang@chaos.utexas.edu

received 17 July 2009; accepted in final form 14 August 2009; published August 2009
published online 15 September 2009

Abstract
We 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.

PACS
87.18.Gh - Cell-cell communication; collective behavior of motile cells.
47.63.Gd - Swimming microorganisms.
05.65.+b - Self-organized systems.

© EPLA 2009