FIG. 2.

Deletion of M. tuberculosis pknH increases resistance to acidified nitrite stress. (A) Survival (CFU) of the pknH strains following exposure to 3 mM NaNO₂ in acidified medium (pH 5.4) for 48 h was determined and compared with the CFU obtained from pH 5.4 medium lacking NaNO₂. Error bars represent standard deviations obtained for triplicate cultures of each strain. The values obtained for the ΔpknH mutant strain are significantly different (P < 0.0001) from those for the wild type and the complement. (B) Effect of oxidizing stresses on viability of the pknH strains. Bacteria were grown in 7H9-Tween-ADS medium, exposed to different stressing reagents (10 mM H₂O₂ or 50 mM paraquat) for 48 h, and plated to determine viability. The bars represent mean percent survival (% CFU treated/untreated) for each treatment, and the error bars indicate standard deviations obtained from triplicate cultures.