Enzymatic Characterization and In Vivo Function of Five Terminal Oxidases in Pseudomonas aeruginosa

The ubiquitous opportunistic pathogenPseudomonas aeruginosa has five aerobic terminal oxidases:bo 3 -type quinol oxidase (Cyo), cyanide-insensitive oxidase (CIO),aa 3 -type cytochromec oxidase (aa 3 ), and twocbb 3 -type cytochromec oxidases (cbb 3 -1 andcbb 3 -2). These terminal oxidases are differentially regulated under various growth conditions and are thought to contribute to the survival of this microorganism in a wide variety of environmental niches. Here, we constructed multiple mutant strains ofP. aeruginosa that express only one aerobic terminal oxidase to investigate the enzymatic characteristics andin vivo function of each enzyme. TheKm values of Cyo, CIO, andaa 3 for oxygen were similar and were 1 order of magnitude higher than those ofcbb 3 -1 andcbb 3 -2, indicating that Cyo, CIO, andaa 3 are low-affinity enzymes and thatcbb 3 -1 andcbb 3 -2 are high-affinity enzymes. Althoughcbb 3 -1 andcbb 3 -2 exhibited different expression patterns in response to oxygen concentration, they had similarKm values for oxygen. Bothcbb 3 -1 andcbb 3 -2 utilized cytochromec 4 as the main electron donor under normal growth conditions. The electron transport chains terminated bycbb 3 -1 andcbb 3 -2 generate a proton gradient across the cell membrane with similar efficiencies. The electron transport chain ofaa 3 had the highest proton translocation efficiency, whereas that of CIO had the lowest efficiency. The enzymatic properties of the terminal oxidases reported here are partially in agreement with their regulatory patterns and may explain the environmental adaptability and versatility ofP. aeruginosa .