FIG 7.

ΔDacA is more susceptible to environmental stress. (A and B) ΔDacA is sensitive to salt stress. The growth (OD₆₀₀) of S. pyogenes in THY medium with various concentrations (0.1 N, 0.2 N, and 0.3 N) of KCl (A) or NaCl (B) was measured at 8 h postinoculation, when S. pyogenes typically reaches the stationary phase. (C) ΔDacA is sensitive to low pH. The growth of S. pyogenes in THY or C medium whose pH was lowered to pH 6 was measured at 8 h postinoculation. (D) ΔDacA has increased sensitivity to oxidative stress. The sensitivity of S. pyogenes strains to oxidative stress was tested by challenging them with methyl viologen (MV). Cells were exposed to 50 mM MV for 3 h in short-term exposure and to 1.7 mM MV for 18 h in long-term exposure. The relative survival rate was determined by comparing viable cell counts with and without MV treatment. The data in the figure are the means and standard errors of the means derived from two independent experiments. The significance of the difference between each mutant and the wild type was calculated by two-way ANOVA (A and B) or one-way ANOVA (C and D) followed by Dunnett’s multiple-comparison test. (A and B) The values of all data points except those from THY are different (P < 0.001) from those of the wild type. (C and D) Asterisks above the bars indicate the significance of the difference (*, P < 0.05; **, P < 0.01; ***, P < 0.001; ****, P < 0.0001) between the mutant and the wild type. The following strains were tested: wild type (WT), dacA deletion mutant (ΔDacA), pde2 deletion mutant (ΔPde2), and gdpP deletion mutant (ΔGdpP).