A bacterial flagellum is driven at its base by a rotary motor comprising a rod and set of rings embedded in the cell wall and cytoplasmic membrane. The energy for rotation is supplied by an electrochemical proton gradient. The motor spins alternately clockwise and counterclockwise, with a bias depending on sensory transduction, for example, on the cell's response to chemical stimuli (chemotaxis). Studies of the biochemistry and physiology of this system are being made with Escherichia coli and a motile Streptococcus. E. Coli is being used because the structure of its motors can be perturbed genetically; Streptococcus is being used because its motors can be energize artificially. Measurements have been made, either with swimming cells or with cells tethered to glass by a flagellum, of protonmotive force, proton flux, torque and speed. Mutants of the torque-generating elements MotA and MotB have been isolated and characterized. This work has led to a model for the motor consistent with existing experimental data that is being subjected to further test. The goal is an understanding of flagellar rotation at the molecular level, or more broadly, of how living things use chemical energy to do mechanical work. %%% Motility is a critical phenomenon of living things. In the world of bacteria, flagellum-mediated swimming movement allows for responses to chemical or physical stimuli (such as nutrients, light, barriers) which are necessary for alleviating colonial overcrowding, sustenance of individual bacteria, and genetic mating. The bacterial flagellum and its motor are tiny, yet effective. In addition to providing an understanding of the molecular basis for biological behavior, the results of this research could find usefulness in nanofabrication or biomaterials research (e.g., using natural or artificial flagella as switches).
