title: Differentiation between electron transport sensing and proton motive force sensing by the Aer and Tsr receptors for aerotaxis.
abstract: Aerotaxis (oxygen-seeking) behaviour in Escherichia coli is a response to changes in the electron transport system and not oxygen per se. Because changes in proton motive force (PMF) are coupled to respiratory electron transport, it is difficult to differentiate between PMF, electron transport or redox, all primary candidates for the signal sensed by the aerotaxis receptors, Aer and Tsr. We constructed electron transport mutants that produced different respiratory H+/e- stoichiometries. These strains expressed binary combinations of one NADH dehydrogenase and one quinol oxidase. We then introduced either an aer or tsr mutation into each mutant to create two sets of electron transport mutants. In vivo H+/e- ratios for strains grown in glycerol medium ranged from 1.46+/-0.18-3.04+/-0.47, but rates of respiration and growth were similar. The PMF jump in response to oxygen was proportional to the H+/e- ratio in each set of mutants (r2=0.986-0.996). The length of Tsr-mediated aerotaxis responses increased with the PMF jump (r2=0.988), but Aer-mediated responses did not correlate with either PMF changes (r2=0.297) or the rate of electron transport (r2=0.066). Aer-mediated responses were linked to NADH dehydrogenase I, although there was no absolute requirement. The data indicate that Tsr responds to changes in PMF, but strong Aer responses to oxygen are associated with redox changes in NADH dehydrogenase I.
authors.affiliation: Division of Microbiology and Molecular Genetics, Loma Linda University, Loma Linda, CA 92350, USA.
authors.forename: Jessica C
authors.initials: JC
authors.lastname: Edwards
authors.forename: Mark S
authors.initials: MS
authors.lastname: Johnson
authors.forename: Barry L
authors.initials: BL
authors.lastname: Taylor
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002633:Chemotaxis / Q000502:physiology*; D004579:Electron Transport; D003576:Electron Transport Complex IV / Q000235:genetics / Q000378:metabolism; D004926:Escherichia coli / Q000502:physiology*; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D036341:Intercellular Signaling Peptides and Proteins; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D008967:Molecular Biology / Q000379:methods; D009154:Mutation; D009245:NADH Dehydrogenase / Q000235:genetics / Q000378:metabolism; D010088:Oxidoreductases / Q000235:genetics / Q000378:metabolism; D010100:Oxygen / Q000378:metabolism; D011522:Protons; D053038:Quorum Sensing
chemical_list: C108679:Aer protein, E coli; D001426:Bacterial Proteins; D002352:Carrier Proteins; D029968:Escherichia coli Proteins; D036341:Intercellular Signaling Peptides and Proteins; D008565:Membrane Proteins; D011522:Protons; C057635:Tsr protein, Bacteria; D010088:Oxidoreductases; C020094:duroquinol oxidase; D009245:NADH Dehydrogenase; D003576:Electron Transport Complex IV; D010100:Oxygen