Adaptation of Aerobically GrowingPseudomonas aeruginosato Copper Starvation

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Abstract
Restricted bioavailability of copper in certain environments can interfere with cellular respiration because copper is an essential cofactor of most terminal oxidases. The global response of the metabolically versatile bacterium and opportunistic pathogenPseudomonas aeruginosato copper limitation was assessed under aerobic conditions. Expression ofcioAB(encoding an alternative, copper-independent, cyanide-resistant ubiquinol oxidase) was upregulated, whereas numerous iron uptake functions (including the siderophores pyoverdine and pyochelin) were expressed at reduced levels, presumably reflecting a lower demand for iron by respiratory enzymes. Wild-typeP. aeruginosawas able to grow aerobically in a defined glucose medium depleted of copper, whereas acioABmutant did not grow. Thus,P. aeruginosarelies on the CioAB enzyme to cope with severe copper deprivation. A quadruplecyo cco1 cco2 coxmutant, which was deleted for all known heme-copper terminal oxidases ofP. aeruginosa, grew aerobically, albeit more slowly than did the wild type, indicating that the CioAB enzyme is capable of energy conservation. However, the expression of acioA′-′lacZfusion was less dependent on the copper status in the quadruple mutant than in the wild type, suggesting that copper availability might affectcioABexpression indirectly, via the function of the heme-copper oxidases.