The ctpA (ccoI) gene product, a putative inner membrane copper-translocating P1B-type ATPase present in many bacteria, has been shown to be involved only in the cbb 3 assembly in Rhodobacter capsulatus and Bradyrhizobium japonicum. ctpA was disrupted in Rubrivivax gelatinosus, and the mutants showed a drastic decrease in both cbb 3 and caa 3 oxidase activities. Inactivation of ctpA results also in a decrease in the amount of the nitrous oxide reductase, NosZ. This pleiotropic phenotype could be partially rescued by excess copper in the medium, indicating that CtpA is likely a copper transporter that supplies copper-requiring proteins in the membrane with this metal. Although CtpA shares significant sequence homologies with the homeostasis copper efflux P1B-type ATPases including the bacterial CopA and the human ATP7A and ATP7B, disruption of ctpA did not result in any sensitivity to excess copper. This indicates that the CtpA is not crucial for copper tolerance but is involved in the assembly of membrane and periplasmic copper enzymes in this bacterium. The potential roles of CtpA in bacteria in comparison with CopA are discussed.

The appearance of oxygen in the Earth's atmosphere via oxygenic photosynthesis required strict anaerobes and obligate phototrophs to cope with the presence of this toxic molecule. Here we show that in the anoxygenic phototroph Rubrivivax gelatinosus, the terminal oxidases (cbb 3 , bd, and caa 3 ) expand the range of ambient oxygen tensions under which the organism can initiate photosynthesis. Unlike the wild type, the cbb 3 ؊ /bd ؊ double mutant can start photosynthesis only in deoxygenated medium or when oxygen is removed, either by sparging cultures with nitrogen or by co-inoculation with strict aerobes bacteria. In oxygenated environments, this mutant survives nonphotosynthetically until the O 2 tension is reduced. The cbb 3 and bd oxidases are therefore required not only for respiration but also for reduction of the environmental O 2 pressure prior to anaerobic photosynthesis. Suppressor mutations that restore respiration simultaneously restore photosynthesis in nondeoxygenated medium. Furthermore, induction of photosystem in the cbb 3 ؊ mutant led to a highly unstable strain. These results demonstrate that photosynthetic metabolism in environments exposed to oxygen is critically dependent on the O 2 -detoxifying action of terminal oxidases.

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