Escherichia coli senses the oxygen concentration of its environment via the Aer and Tsr receptors, and swims to an oxygen concentration that provides optimal energy generation. Aer and Tsr do not sense oxygen per se but, sense the internal energy state via the electron transport system (ETS) in a previously unidentified mechanism. Proton motive force (PMF) and electron flow were proposed as possible sensory signals but, distinguishing between the two was not possible, previously, in live, motile cells. I differentiated PMF from electron flow by creating a series of ETS mutant strains that express ternary combinations of i) aerotaxis receptors, ii) NADH dehydrogenases and iii) cytochrome oxidases. Since the ETS components differ in the number of protons translocated per electron traversing the ETS, the H+/e- ratios for the constructed strains varied from 1.5 to 3. Correlation analysis between the in vivo H+/e- ratio and PMF measurements revealed a close correlation (R2=0.99) between the two parameters. Only minor differences in respiration rate were observed in the constructed strains. The aerotaxis behavior of Aer and Tsr in these strains was examined in aerotactic temporal assays and in semi-soft agar. There was a positive correlation (R2=0.99) between the Tsr-mediated response and PMF. This evidence indicates that Tsr is likely sensing PMF in the aerotactic response. In contrast, the Aer-mediated response did not correlate with any of the bioenergetic parameters examined here. Aer-mediated aerotaxis was enhanced by the presence of NADH dehydrogenase 1 (NDH-1), but also occurred in the absence of NDH-1. Previous work indicated that Aer responds to redox changes and Aer may be able to sense the redox state of NDH-1 in addition to other cellular redox molecules. In conclusion, this work establishes PMF as the energetic signal sensed by Tsr and is congruent with a redox-sensing mechanism for Aer.

LLU Discipline

Microbiology and Molecular Genetics


Microbiology, Molecular Biology and Biochemistry


Graduate School

First Advisor

Barry L. Taylor

Second Advisor

Penelope J. Duerksen-Hughes

Third Advisor

Robert P. Gunsalus

Fourth Advisor

Mark S. Johnson

Fifth Advisor

Anthony J. Zuccarelli

Degree Name

Doctor of Philosophy (Medical Science)

Degree Level


Year Degree Awarded


Date (Title Page)




Library of Congress/MESH Subject Headings

Escherichia Coli -- genetics; Escherichia Coli Proteins -- genetics; Electron Transport -- physiology; Proton-Motive Force -- physiology; Chemotaxis -- genetics.



Page Count

xiv; 214

Digital Format


Digital Publisher

Loma Linda University Libraries

Usage Rights

This title appears here courtesy of the author, who has granted Loma Linda University a limited, non-exclusive right to make this publication available to the public. The author retains all other copyrights.


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Collection Website



Loma Linda University. Del E. Webb Memorial Library. University Archives