title: Involvement of transport in Rhodobacter sphaeroides chemotaxis.
abstract: The chemotactic response to a range of chemicals was investigated in the photosynthetic bacterium Rhodobacter sphaeroides, an organism known to lack conventional methyl-accepting sensory transduction proteins. Strong attractants included monocarboxylic acids and monovalent cations. Results suggest that the chemotactic response required the uptake of the chemoeffector, but not its metabolism. If a chemoeffector could block the uptake of another attractant, it also inhibited chemotaxis to that attractant. Sodium benzoate was not an attractant but was a competitive inhibitor of the propionate uptake system. Binding in an active uptake system was therefore insufficient to cause a chemotactic response. At different concentrations, benzoate either blocked propionate chemotaxis or reduced the sensitivity of propionate chemotaxis, an effect consistent with its role as a competitive inhibitor of uptake. Bacteria only showed chemotaxis to ammonium when grown under ammonia-limited conditions, which derepressed the ammonium transport system. Both chemotaxis and uptake were sensitive to the proton ionophore carbonyl cyanide m-chlorophenylhydrazone, suggesting an involvement of the proton motive force in chemotaxis, at least at the level of transport. There was no evidence for internal pH as a sensory signal. These results suggest a requirement for the uptake of attractants in chemotactic sensing in R. sphaeroides.
mesh_terms: D000085:Acetates / Q000378:metabolism / Q000494:pharmacology; D001693:Biological Transport, Active; D002630:Chemotactic Factors / Q000378:metabolism* / Q000494:pharmacology; D002633:Chemotaxis / Q000187:drug effects; D006863:Hydrogen-Ion Concentration; D011422:Propionates / Q000378:metabolism / Q000494:pharmacology; D012242:Rhodobacter sphaeroides / Q000378:metabolism / Q000502:physiology*
chemical_list: D000085:Acetates; D002630:Chemotactic Factors; D011422:Propionates