Collective motion and density fluctuations in bacterial colonies

Flocking birds, fish schools, and insect swarms are familiar examples of collective motion that plays a role in a range of problems, such as spreading of diseases. Models have provided a qualitative understanding of the collective motion, but progress has been hindered by the lack of detailed experi...

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Published in:	Proceedings of the National Academy of Sciences - PNAS Vol. 107; no. 31; pp. 13626 - 13630
Main Authors:	Zhang, H. P., Be'er, Avraham, Florin, E.-L., Swinney, Harry L., Goldstein, Raymond E.
Format:	Journal Article
Language:	English
Published:	United States National Academy of Sciences 03-08-2010 National Acad Sciences
Subjects:	Bacillus subtilis Bacillus subtilis - cytology Bacteria Bacteriology Biological Sciences Biophysics Chemical suspensions Cluster Analysis Colonies Correlations Data processing Density Flagella Gram-positive bacteria Herds Hydrodynamics Imaging Kinetics Microbial Viability Models, Biological Motion Particle interactions Particle motion Physical Sciences Spreading Swarms Tails
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Summary:	Flocking birds, fish schools, and insect swarms are familiar examples of collective motion that plays a role in a range of problems, such as spreading of diseases. Models have provided a qualitative understanding of the collective motion, but progress has been hindered by the lack of detailed experimental data. Here we report simultaneous measurements of the positions, velocities, and orientations as a function of time for up to a thousand wild-type Bacillus subtilis bacteria in a colony. The bacteria spontaneously form closely packed dynamic clusters within which they move cooperatively. The number of bacteria in a cluster exhibits a power-law distribution truncated by an exponential tail. The probability of finding clusters with large numbers of bacteria grows markedly as the bacterial density increases. The number of bacteria per unit area exhibits fluctuations far larger than those for populations in thermal equilibrium. Such "giant number fluctuations" have been found in models and in experiments on inert systems but not observed previously in a biological system. Our results demonstrate that bacteria are an excellent system to study the general phenomenon of collective motion.
Bibliography:	ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 ObjectType-Article-2 ObjectType-Feature-1 Author contributions: H.P.Z., A.B., E.-L.F., and H.L.S. designed research; H.P.Z., A.B., E.-L.F., and H.L.S. performed research; H.P.Z., A.B., E.-L.F., and H.L.S. analyzed data; and H.P.Z., A.B., E.-L.F., and H.L.S. wrote the paper. Edited by Raymond E. Goldstein, University of Cambridge, Cambridge, United Kingdom, and accepted by the Editorial Board June 23, 2010 (received for review February 18, 2010)
ISSN:	0027-8424 1091-6490
DOI:	10.1073/pnas.1001651107