ELECTRON TRANSPORT-DEPENDENT TAXIS IN RHODOBACTER-SPHAEROIDES

Rhodobacter sphaeroides showed chemotaxis to the terminal electron accepters oxygen and dimethyl sulfoxide, and the responses to these effecters were shown to be influenced by the relative activities df the different electron transport pathways. R. sphaeroides cells tethered by their flagella showed a step-down response tea decrease in the oxygen or dimethyl sulfoxide concentration when using them as terminal accepters. Bacteria using photosynthetic electron transport, however, showed a step down response to oxygen. addition, Addition of the proton ionophore carbonyl cyanide 4-trifluoromethoxyphenylhydrazone did not cause a transient behavioral response, although it decreased the electrochemical proton gradient (Delta p) and increased the rate of electron transport, However, removal of the ionophore, which caused an increase in Delta p and a decrease in the electron transport rate, resulted in a step-down response. Together, these data suggest that behavioral responses of R. sphaeroides to electron transport effecters are caused by changes in the rate of electron transport rather than changes in Delta p.