FIG. 4.

Resistance to superoxide. (A) Influence of methyl viologen on the growth of WT (closed diamonds), hfq (closed squares), sodB (closed triangles), and sodC (open circles) strains. Cells were grown in GAS medium containing 0 to 100 μM methyl viologen to late stationary growth phase. Residual growth corresponds to the ratio of maximal growth yield in GAS medium supplemented with methyl viologen to maximal growth yield in GAS medium for each strain. The results are the averages from three independent experiments, and the bars represent the standard deviations. (B) Influence of pyrogallol on bacterial survival. Cells of WT (closed diamonds), hfq (closed squares), and sodC (open circles) strains were grown in GAS medium, collected by centrifugation, and incubated in PBS buffer containing 2 mM pyrogallol and 1,000 U ml⁻¹ of bovine liver catalase. Aliquots were removed periodically, and survival was estimated by serial dilution and plating on LB plates. The results are the means from five independent experiments, and the standard deviations are indicated.