THE AER PROTEIN AND THE SERINE CHEMORECEPTOR TSR INDEPENDENTLY SENSE INTRACELLULAR ENERGY-LEVELS AND TRANSDUCE OXYGEN, REDOX, AND ENERGY SIGNALS FOR ESCHERICHIA-COLI BEHAVIOR

We identified a protein, Aer, as a signal transducer that senses intra cellular energy levels rather than the external environment and that t ransduces signals for aerotaxis (taxis to oxygen) and other energy-dep endent behavioral responses in Escherichia coli, Domains in Aer are si milar to the signaling domain in chemotaxis receptors and the putative oxygen-sensing domain of some transcriptional activators, A putative FAD-binding site in the N-terminal domain of Aer shares a consensus se quence with the NifL, Bat, and Wc-1 signal-transducing proteins that r egulate gene expression in response to redox changes, oxygen, and blue light, respectively, A double mutant deficient in aer and tsr, which codes for the serine chemoreceptor, was negative for aerotaxis, redox taxis, and glycerol taxis, each of which requires the proton motive fo rce and/or electron transport system for signaling, We propose that Ae r and Tsr sense the proton motive force or cellular redox state and th ereby integrate diverse signals that guide E. coli to environments whe re maximal energy is available for growth.