FIG. 3.

(A) Growth curve of F. tularensis LVS and sodB_Ft. MHB (25 ml) in a 125-ml flask was inoculated with 1 ml of an overnight culture of F. tularensis LVS or sodB_Ft and agitated at 175 rpm and 37°C in a shaking incubator. Aliquots were removed at the times indicated to measure optical density at 600 nm (OD₆₀₀), and 10-fold dilutions were plated on modified chocolate agar for the determination of CFU levels. (B) Effect of sodB mutation on sensitivity to H₂O₂. F. tularensis LVS and sodB_Ft mutants were grown in MHB to an OD of 0.2. The indicated concentrations of H₂O₂ were then added, and the cultures were allowed to grow for 48 h in a shaking incubator. OD readings were taken every 4 h. (C) Aliquots were removed from the cultures grown in the presence of 1 mM of H₂O₂ at the times indicated and plated on modified chocolate agar plates to determine the CFU counts. Percent survival was calculated using the mean of the results obtained with duplicate samples at the timed intervals and compared to data at 0 h. All results are representative of two independent experiments.