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Much is known about the motile behavior of the bacterium Escherichia coli. Early work on tracking E. coli and learning about its biased random walk was followed by the realization that bacterial flagella rotate rather than wave or beat. Flagellar rotation is controlled by chemoreceptors at the cell surface. Receptor methylation is required for adaptation on the second time scale, which enables cells to make temporal comparisons and swim up spatial gradients of attractants. Without methylation, one still observes partial adaptation, on the minute time scale, as motors remodel and shift their operating points. Motors also adapt to changes in viscous load. When the load suddenly increases, additional force-generating units are added one by one; thus, the flagellum is a mechanosensor as well as a device for generating thrust. Flagellar filaments grow at their distal ends at a rate that does not to depend upon initial lengths. Single-file diffusion appears to be adequate to get flagellin subunits from the base to the tip.