Bacterial motility and chemotaxis.
Bacteria swim using the only rotary motor identified in biology. The membrane bound motor uses the gradient of protons set up across the cytoplasmic membrane to drive the rotation of a semi-rigid protein helix, the flagellum. Free-swimming bacteria randomly change direction every few seconds, but if a gradient is encountered the direction-changing frequency can be biased to move the bacterium in a favourable direction. Bacteria respond to changes in chemical concentration, oxygen levels, pH, the intensity or wavelength of light, temperature and in some cases even the Earth's magnetic field and integrate the signals to move towards or maintain the cells in optimum conditions for growth and division. They also adapt to the changes, leaving them free to respond to any subsequent stimuli. Therefore bacteria have something akin to a primitive nervous system, with a sensory system which can respond and adapt to changes and integrate physical and chemical signals. Chemotaxis and motility are involved in infection, both positive (rhizobia) and negative (pathogens) and an understanding of the unique nature of motility and chemotaxis in bacteria may make it possible to control infection. This review will give a brief general overview of current knowledge of bacterial motility and chemotaxis but for more detailed analysis readers are referred to some more specific recent reviews.