Fig. 4.

Resistance of the CcoN3- and CcoN4-containing cbb₃ isoforms to nitrite and cyanide. (A) Growth profiles of PAO1 and the ccoN3 mutant in LB medium in the presence or absence of 20 mM KNO₂ under low-oxygen (0.5%) conditions. (B) Growth profiles of STO7 transformed with plasmids expressing CcoN1O1P1, CcoN2O2P2, CcoN3O1P1, or CcoN3O2P2. The strains were cultured aerobically in 96-well plates. (C) Growth profiles of PAO1 and the ccoN4 mutant in LB medium in the presence or absence of 300 μM KCN under low-oxygen (0.5%) conditions. (D) Oxygen consumption activities of the membrane fraction of the cells of STO7 transformed with plasmids expressing CcoN1O1P1, CcoN2O2P2, CcoN4O1P1, or CcoN4O2P2. Ascorbate-reduced TMPD was used as an electron donor for the reaction. KCN was added at various concentrations in the reaction mixture. Values are shown as percentages of the maximal activity level in the absence of KCN. Data are representatives of at least two independent experiments.