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Applied and Environmental Microbiology, July 2006, p. 4987-4994, Vol. 72, No. 7
0099-2240/06/$08.00+0 doi:10.1128/AEM.00158-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.
Sibley School of Mechanical and Aerospace Engineering,1 School of Chemical and Biomolecular Engineering, Cornell University, Ithaca, New York 148532
Received 20 January 2006/ Accepted 19 April 2006
An ability to monitor bacterial locomotion and collective dynamics is crucial to our understanding of a number of well-characterized phenotypes including biofilm formation, chemotaxis, and virulence. Here, we report the tracking of multiple swimming Escherichia coli cells in three spatial dimensions and at single-cell resolution using a novel three-dimensional (3D) defocused particle tracking (DPT) method. The 3D trajectories were generated for wild-type Escherichia coli strain RP437 as well as for isogenic derivatives that display smooth swimming due to a cheA deletion (strain RP9535) or incessant tumbling behavior due to a cheZ deletion (strain RP1616). The 3D DPT method successfully differentiated these three modes of locomotion and allowed direct calculation of the diffusion coefficient for each strain. As expected, we found that the smooth swimmer diffused more readily than the wild type, and both the smooth swimmer and the wild-type cells exhibited diffusion coefficients that were at least two orders of magnitude larger than that of the tumbler. Finally, we found that the diffusion coefficient increased with increasing cell density, a phenomenon that can be attributed to the hydrodynamic disturbances caused by neighboring bacteria.
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