Rotation Measurements of Tethered Cells.

Direct observation of the rotation of tethered cells using optical microscopy is a simple method to examine dynamics of the bacterial flagellar motor. The rotational speed indicates not only the existence of the rotary motor, but also approximate number of stators that are torque-generating units in a motor. Since "run" and "tumble" of the peritrichous cells as Escherichia coli are regulated by the counterclockwise rotation and the clockwise rotation, respectively, rotational direction of the tethered cell is an important clue to understand the chemotactic system of the cells.