title: Compensations for diminished terminal oxidase activity in Escherichia coli: cytochrome bd-II-mediated respiration and glutamate metabolism.
abstract: Escherichia coli possesses cytochrome bo' (CyoABCDE), cytochrome bd-I (CydAB), and cytochrome bd-II (AppBC) quinol oxidases, all of which can catalyze the terminal step in the aerobic respiratory chain, the reduction of oxygen by ubiquinol. Although CydAB has a role in the generation of DeltapH, AppBC has been proposed to alleviate the accumulation of electrons in the quinone pool during respiratory stress via electroneutral ubiquinol oxidation. A cydB mutant strain exhibited lower respiration rates while maintaining a wild type growth rate. Transcriptomic analysis revealed a dramatic up-regulation of AppBC in the cydB strain, accompanied by the induction of genes involved in glutamate/gamma-aminobutyric acid (GABA) antiport, the GABA shunt, the glyoxylate shunt, respiration (including appBC), motility, and osmotic stress. Transcription factor modeling suggests that the underpinning regulation is largely controlled by H-NS, GadX, FlhDC, and AppY. The transcriptional adaptations imply that cydB cells contribute to the proton motive force via consumption of intracellular protons and glutamate/GABA antiport. Indeed, supplementation of culture medium with l-glutamate stimulates growth in a cydB strain. Phenotype analyses of the cydB strain confirm decreased motility and elevated acid resistance and also an elevated cytochrome d spectroscopic signal in cells grown at low pH. We propose a mechanism via which E. coli can compensate for the loss of cytochrome bd-I activity; cytochrome bd-II-mediated quinol oxidation prevents the accumulation of NADH, whereas GABA synthesis/antiport maintains the proton motive force for ATP production.
authors.affiliation: Department of Molecular Biology and Biotechnology, The University of Sheffield, Sheffield S10 2TN, United Kingdom.
authors.forename: Mark
authors.initials: M
authors.lastname: Shepherd
authors.forename: Guido
authors.initials: G
authors.lastname: Sanguinetti
authors.forename: Gregory M
authors.initials: GM
authors.lastname: Cook
authors.forename: Robert K
authors.initials: RK
authors.lastname: Poole
mesh_terms: D002465:Cell Movement; D019069:Cell Respiration; D017937:Cytochrome d Group / Q000235:genetics*; D045303:Cytochromes b / Q000235:genetics*; D004566:Electrodes; D004926:Escherichia coli / Q000201:enzymology*; D015964:Gene Expression Regulation, Bacterial; D005971:Glutamates / Q000737:chemistry; D018698:Glutamic Acid / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D015233:Models, Statistical; D010100:Oxygen / Q000737:chemistry; D010101:Oxygen Consumption; D013053:Spectrophotometry / Q000379:methods
chemical_list: D005971:Glutamates; D018698:Glutamic Acid; D017937:Cytochrome d Group; D045303:Cytochromes b; D010100:Oxygen
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