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Oxygen reactivity of both respiratory oxidases in Campylobacter jejuni: the cydAB genes encode a cyanide-resistant, low-affinity oxidase that is not of the cytochrome bd type.

Jackson RJ, Elvers KT, Lee LJ, Gidley MD, Wainwright LM, Lightfoot J, Park SF, Poole RK

Department of Molecular Biology and Biotechnology, The University of Sheffield, Western Bank, Sheffield S10 2TN, UK.

The microaerophilic bacterium Campylobacter jejuni is a significant food-borne pathogen and is predicted to possess two terminal respiratory oxidases with unknown properties. Inspection of the genome reveals an operon (cydAB) apparently encoding a cytochrome bd-like oxidase homologous to oxidases in Escherichia coli and Azotobacter vinelandii. However, C. jejuni cells lacked all spectral signals characteristic of the high-spin hemes b and d of these oxidases. Mutation of the cydAB operon of C. jejuni did not have a significant effect on growth, but the mutation reduced formate respiration and the viability of cells cultured in 5% oxygen. Since cyanide resistance of respiration was diminished in the mutant, we propose that C. jejuni CydAB be renamed CioAB (cyanide-insensitive oxidase), as in Pseudomonas aeruginosa. We measured the oxygen affinity of each oxidase, using a highly sensitive assay that exploits globin deoxygenation during respiration-catalyzed oxygen uptake. The CioAB-type oxidase exhibited a relatively low affinity for oxygen (K(m) = 0.8 microM) and a V(max) of >20 nmol/mg/s. Expression of cioAB was elevated fivefold in cells grown at higher rates of oxygen provision. The alternative, ccoNOQP-encoded cyanide-sensitive oxidase, expected to encode a cytochrome cb'-type enzyme, plays a major role in the microaerobic respiration of C. jejuni, since it appeared to be essential for viability and exhibited a much higher oxygen affinity, with a K(m) value of 40 nM and a V(max) of 6 to 9 nmol/mg/s. Low-temperature photodissociation spectrophotometry revealed that neither oxidase has ligand-binding activity typical of the heme-copper oxidase family. These data are consistent with cytochrome oxidation during photolysis at low temperatures.

Published 15 February 2007 in J Bacteriol, 189(5): 1604-15.
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