Figure 5.

Significantly reduced NIR and NOR activities in mucA mutant P. aeruginosa account for the sensitivity to HNO₂. (A) Relative activities of NAR, NIR, and NOR in FRD1 (lane 2) and FRD1/pmucA (lane 3), normalized to that of the well-characterized laboratory strain PAO1 (lane 1). Each assay was performed in triplicate, and the mean ± SEM is presented. A schematic diagram of the P. aeruginosa anaerobic respiration pathway is shown. Bacteria were grown in LB (pH 6.5) containing 100 mM NO₃^– for 15 hours under anaerobic conditions. (B) P. aeruginosa strains were incubated anaerobically in LB containing 15 mM NO₂^–, pH 6.5. After 4 days at 37°C, NO₂^– levels were measured in triplicate. All other mucA mutant clinical isolates were among those described in Supplemental Table 1. For the media-only control, no bacteria were used. ND, not detected. (C) Anaerobic sensitivity of FRD1 and FRD1 norCB mutant exposed to NO₂^– at pH 6.5. Experimental conditions were identical to those used in Figure 2B. Δ, deletion of a specific gene. *P < 0.01 versus FRD1.