Fig. 1.

Multiple cbb₃ isoforms in P. aeruginosa. (A) Sixteen isoforms of cbb₃ could be produced via combinations of the isosubunits encoded by four cco gene clusters. cbb₃-1 and cbb₃-2 are shown in boxes. (B) Cytochrome c oxidase activity of the isoforms visualized in blue color by the Nadi assay. WT and Δcbb₃ indicate PAO1 and the ccoN1O1Q1P1 ccoN2O2Q2P2 double-mutant MCb12, respectively. Triple-digit numbers indicate the combination of the CcoN, CcoO, and CcoP isosubunits. For example, 111, 212, 321, and 422 indicate CcoN1O1P1, CcoN2O1P2, CcoN3O2P1, and CcoN4O2P2, respectively. The isoforms were expressed in strain STO7 with the expression plasmids shown in Fig. S1.