FIG. 7.

Idealized sequence of events in a tumble caused by the reversal of a single motor. The upper timeline indicates the direction of motor rotation of the filament causing the tumble, and the lower timeline indicates the behavior as judged by motion of the cell body. From left to right: 1, a bacterium swimming along its original trajectory with all left-handed normal filaments; 2, a motor reversal (CCW to CW) causing the filament to start unbundling and the cell body to deflect slightly; 3, initiation of the transformation of the filament from the left-handed normal form to the right-handed semicoiled form and the beginning of a large deflection of the cell body opposite the previous small deflection; 4, complete transformation of the filament to the semicoiled form and reorientation of the cell along a new trajectory; 5, movement of the cell along the new trajectory, propelled by a normal bundle turning CCW and a semicoiled filament turning CW which has partially transformed to the right-handed curly 1 form; 6, complete conversion of the filament to the curly 1 form, which is flexible enough to twist loosely around the bundle; 7, the motor reversing again (CW to CCW), causing the curly 1 form to revert to normal; and 8, after the filament has rejoined the bundle.