FIG. 5.

Role of SodA in acid tolerance and adaptation. (A) S. aureus 8325-4 (●,○) and SPW1 (▴,▵) were grown and treated with acid as described in Materials and Methods. Exponential-phase cells were either incubated at pH 4 (37°C) for 1 h (○,▵) or untreated (●,▴) prior to pH 2 assault. Viability was determined by plating on CDM agar. Results are representative of three independent experiments showing less than fivefold variability. (B) Induction of sodA expression and SOD activity during acid adaptation. Exponential-phase cells (OD₆₀₀ = 0.8) were resuspended in CDM pH 7 (●,▴) or pH 4 (○,▵). Expression of sodA (SPW1, ▴,▵) and total SOD activity (8325-4, ●,○) were determined as described in Materials and Methods. Error bars represent the standard deviations of three independent samples.