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Swarming Escherichia coli Introduction When grown on 0.45% Eiken agar in rich medium, cells of E. coli elongate, produce more flagella, and move over the surface of the agar in a coordinated manner. The chemotaxis system in not thought to be required. As you will see in the movies, taken at 30 degrees C, the cells swirl about in rafts or packs. At the edge of the swarm they form a monolayer. At the very edge, cells are nearly stationary. Farther back, closer to the point of inoculation, cells pile up in multilayers and are very active. The videos were made in bright-phase contrast. Smoke particles on the top surface near the swarm edge were visualized in dark field by adding a fiber-optic illuminator oriented about 10 degrees from horizontal. They diffuse locally but are not perturbed by the swarming cells, which shows that the surface of the swarm is stationary. We think it is covered by a surfactant monolayer pinned at its edges. The smoke particles were about 0.2 microns in diameter. The cells were about 1 micron in diameter by 5 microns long. Movies, cells in phase contrast An E. coli swarm Smoke particles in darkfield and cells in phase contrast Swarm overtaking smoke particle Swarm overtaking a second smoke particle Reference Zhang, R., Turner, L. and Berg, H.C. Escherichia coli swarm under a stationary surfactant layer. PNAS submitted.

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Last modified Tuesday, July 23, 2008.