Expression of multiple<i>cbb</i>₃cytochrome<i>c</i>oxidase isoforms by combinations of multiple isosubunits in<i>Pseudomonas aeruginosa</i>

Abstract

The ubiquitous opportunistic human pathogen <i>Pseudomonas aeruginosa</i> has five terminal oxidases for aerobic respiration and uses them under different growth conditions. Two of them are <i>cbb</i>₃-type cytochrome <i>c</i> oxidases encoded by the gene clusters <i>ccoN1O1Q1P1</i> and <i>ccoN2O2Q2P2</i>, which are the main terminal oxidases under high- and low-oxygen conditions, respectively. <i>P. aeruginosa</i> also has two orphan gene clusters, <i>ccoN3Q3</i> and <i>ccoN4Q4</i>, encoding the core catalytic CcoN isosubunits, but the roles of these genes have not been clarified. We found that 16 active <i>cbb</i>₃ isoforms could be produced by combinations of four CcoN, two CcoO, and two CcoP isosubunits. The CcoN3- or CcoN4-containing isoforms were produced in the WT cell membrane in response to nitrite and cyanide, respectively. The strains carrying these isoforms were more resistant to nitrite or cyanide under low-oxygen conditions. These results indicate that <i>P. aeruginosa</i> gains resistance to respiratory inhibitors using multiple <i>cbb</i>₃ isoforms with different features, which are produced through exchanges of multiple core catalytic isosubunits.