title: 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.
abstract: 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.
authors.affiliation: Department of Molecular Biology and Biotechnology, The University of Sheffield, Western Bank, Sheffield S10 2TN, UK.
authors.forename: Rachel J
authors.initials: RJ
authors.lastname: Jackson
authors.forename: Karen T
authors.initials: KT
authors.lastname: Elvers
authors.forename: Lucy J
authors.initials: LJ
authors.lastname: Lee
authors.forename: Mark D
authors.initials: MD
authors.lastname: Gidley
authors.forename: Laura M
authors.initials: LM
authors.lastname: Wainwright
authors.forename: James
authors.initials: J
authors.lastname: Lightfoot
authors.forename: Simon F
authors.initials: SF
authors.lastname: Park
authors.forename: Robert K
authors.initials: RK
authors.lastname: Poole
mesh_terms: D016123:Campylobacter jejuni / Q000201:enzymology* / Q000254:growth & development; D002248:Carbon Monoxide / Q000378:metabolism; D003486:Cyanides / Q000494:pharmacology*; D003580:Cytochromes / Q000235:genetics / Q000502:physiology*; D004579:Electron Transport; D045222:Electron Transport Chain Complex Proteins / Q000235:genetics / Q000502:physiology*; D007874:Leghemoglobin / Q000378:metabolism; D009211:Myoglobin / Q000378:metabolism; D010101:Oxygen Consumption; D010641:Phenotype; D013053:Spectrophotometry
chemical_list: D003486:Cyanides; D003580:Cytochromes; D045222:Electron Transport Chain Complex Proteins; D007874:Leghemoglobin; D009211:Myoglobin; C095131:oxyleghemoglobin; C017595:oxymyoglobin; D002248:Carbon Monoxide