title: The gradient-sensing mechanism in bacterial chemotaxis.
abstract: A "temporal gradient apparatus" has been developed that allows the motility of bacteria to be studied after they have been subjected to a sudden change from one uniform concentration of attractant to another. A sudden decrease elicits the tumbling response observed with spatial gradients; it was found, however, that a sudden increase also elicits a response, namely supercoordinated swimming. This demonstrates that chemotaxis is achieved by modulation of the incidence of tumbling both above and below its steady-state value. The initial responses gradually revert to the steady-state motility pattern characteristic of a uniform distribution of attractant. The apparent detection of a spatial gradient by the bacteria therefore involves an actual detection of a temporal gradient experienced as a result of movement through space. Potential models for the chemotactic response based on some "memory" mechanism are discussed.
mesh_terms: D002465:Cell Movement; D002633:Chemotaxis; D008954:Models, Biological; D010827:Physiology / Q000295:instrumentation; D012486:Salmonella typhimurium; D012694:Serine; D013997:Time Factors
chemical_list: D012694:Serine