Bacterial chemoreceptors: recent progress in structure and function.

The behavior of a bacterial cell is determined by the interplay between transmembrane receptor molecules and a cytoplasmic kinase that is linked to the flagellar apparatus. In the absence of external stimulus, a balance exists between stresses in the periplasmic region of receptor molecules, and compensating cytoplasmic forces. A response, positive or negative, is due to a temporary disturbance in this balance, with corresponding alterations in kinase activity, and ultimately, of swimming behavior. Methylation acts to restore the balance by changing the properties of the receptor. Because methylation is slow, a response will continue for a period of time following stimulation. The mechanisms by which these processes occur are now being elucidated at the molecular level, and should soon make bacterial chemotaxis the first available picture of a complete sensory system.