An Aerobic Exercise: Defining the Roles of Pseudomonas aeruginosa Terminal Oxidases

The opportunistic pathogen Pseudomonas aeruginosa encodes a large and diverse complement of aerobic terminal oxidases, which is thought to contribute to its ability to thrive in settings with low oxygen availability. In this issue, Arai et al. (J. Bacteriol. 196:4206 – 4215, 2014, doi:http://dx.doi.org/10.1128/JB.02176-14) present a thorough characterization of these five complexes, enabling a more detailed understanding of aerobic respiration in this organism. Although the Earth’s atmosphere contains approximately 21%oxygen, bacteria in environments that are ostensibly aerobic still encounter zones where the concentration is much lower, due to the effects of oxygen solubility, low diffusibility, and consump-tion by neighboring cells. Many bacteria cope with this in part through the use of branched respiratory chains that can be mod-ulated in response to changing conditions (1). Aerobic terminal oxidases, which catalyze electron transfer from the respiratory ap-paratus to oxygen, vary in their affinities and efficiencies (2). Five such enzymes have been identified in the opportunistic pathogen Pseudomonas aeruginosa (Fig. 1), and these are thought to contrib-ute to its ability to thrive under hypoxia (1, 3–8). A diverse collec