FIG. 3.

Aerobic induction of NADH oxidase activity in S. mutans wild-type strain GS-5 and the ΔahpC Δnox-1, Δnox-2, and ΔahpC Δnox-1 Δnox-2 mutants on TYG (A) and TYM (B) media. Anaerobically grown cultures in early log phase were exposed to air and induced at 37°C by shaking under air. Growth was monitored by measuring the optical density at 660 nm of cultures of wild-type (open squares), ΔahpC Δnox-1 (closed triangles), and Δnox-2 (gray circles) cells. At the time course before and after exposure to air, the cells were harvested and NADH oxidase activity in cell extracts was assayed for wild-type (open bars), ΔahpC Δnox-1 (black bars), and Δnox-2 (shaded bars) cells. Results shown are representative of three repeated experiments.