FIG. 9.

Effect of osu on survival during oxidative stress. A. Survival of wild-type (wt)(•), ΩosuA (▪) and osuR (▴) strains following exposure to atmospheric oxygen. Mid-log-phase cells (A₅₅₀ of 0.35) grown in BHIS were exposed to oxygen by shaking at 250 rpm in air at 37°C. Viable cell counts were determined over 72 h. Inset, real-time RT-PCR analysis of osuA expression during oxygen exposure (ox) or under anaerobic conditions (an). The relative n-fold increase in expression is compared to anaerobic conditions, which were normalized to 1. B. Sensitivity of ΩosuA and osuR mutant strains to oxidizing agents. Disk diffusion assays were used to compare wild-type (638R), osuR (IB393), and ΩosuA (IB367) strains. Results are reported as the diameter of growth inhibition around filters treated with the following oxidizing agents: 3% menadione (MD), 3% hydrogen peroxide (H₂O₂), 0.5% t-butyl hydroperoxide (t-butyl). Values are the means from three independent experiments performed in triplicate.