The bacterial flagellar motor.

The bacterial flagellar motor is a remarkable molecular machine that converts chemical energy into work. Knowledge of the structure, genetics, and dynamics of the motor has expanded steadily. Recent progress is reviewed, with an emphasis on the dynamics of flagellar rotation. Previous results with tethered cells, which rotate slowly, are contrasted with recent work on swimming cells, whose motors turn very rapidly. Genetic evidence delineates a small set of proteins that are likely to participate directly in the process of torque generation. An explicit hypothesis for torque generation is described, in which roles are envisaged for each of these proteins.