Organization of the Electron Transfer Chain to Oxygen in the Obligate Human Pathogen Neisseria gonorrhoeae : Roles for Cytochromes c 4 and c 5 , but Not Cytochrome c 2 , in Oxygen Reduction

AlthoughNeisseria gonorrhoeae is a prolific source of eightc -type cytochromes, little is known about how its electron transfer pathways to oxygen are organized. In this study, the roles in the respiratory chain to oxygen of cytochromesc 2 ,c 4 , andc 5 , encoded by the genescccA ,cycA , andcycB , respectively, have been investigated. Single mutations in genes for either cytochromec 4 orc 5 resulted in an increased sensitivity to growth inhibition by excess oxygen and small decreases in the respiratory capacity of the parent, which were complemented by the chromosomal integration of an ectopic, isopropyl-β-d -thiogalactopyranoside (IPTG)-inducible copy of thecycA orcycB gene. In contrast, acccA mutant reduced oxygen slightly more rapidly than the parent, suggesting thatcccA is expressed but cytochromec 2 is not involved in electron transfer to cytochrome oxidase. The deletion ofcccA increased the sensitivity of thecycB mutant to excess oxygen but decreased the sensitivity of thecycA mutant. Despite many attempts, a double mutant defective in both cytochromesc 4 andc 5 could not be isolated. However, a strain with the ectopically encoded, IPTG-induciblecycB gene with deletions in bothcycA andcycB was constructed: the growth and survival of this strain were dependent upon the addition of IPTG, so gonococcal survival is dependent upon the synthesis of either cytochromec 4 orc 5 . These results define the gonococcal electron transfer chain to oxygen in which cytochromesc 4 andc 5 , but not cytochromec 2 , provide alternative pathways for electron transfer from the cytochromebc 1 complex to the terminal oxidase cytochromecbb 3 .