FIG. 1.

Rgg is involved in repression of H₂O₂ resistance. (A) Effects of H₂O₂ on the ODs of O/N cultures. Bacteria from e-stat cultures were inoculated into fresh THY at different concentrations of H₂O₂. The OD₆₀₀s of standing cultures were measured after an O/N (20-h) incubation at 37°C. The results from five independent cultures are expressed as mean growth yield percentages ± SD (OD₆₀₀s in the presence of H₂O₂ divided by the averaged OD₆₀₀s without H₂O₂). (B) Ability of GAS to establish a replicative state in the presence of H₂O₂. Bacteria from e-stat cultures were inoculated into fresh THY containing 750 μM H₂O₂. The bacteria were incubated at 37°C as standing cultures, and the OD₆₀₀s were measured at 1-hour intervals. The results from five independent cultures are expressed as defined for panel A. (C) Effect of Rgg deficiency on the microaerophilic growth of GAS. Bacteria from e-stat cultures were inoculated into fresh THY. The bacteria were incubated at 37°C as standing cultures, and the OD₆₀₀s were measured at 1-hour intervals. The results from five independent cultures are expressed as mean OD₆₀₀ ± SD. (D) H₂O₂ sensitivity of GAS in PBS. Bacteria were harvested from different growth phases (as defined panel C), and after being washed with PBS, they were exposed in PBS to 4 mM H₂O₂ for 2 h at 37°C. To study whether GAS expressed proteins during the H₂O₂ stress, the bacteria were coincubated with 50 μg/ml of chloramphenicol (Chlora). The numbers of viable bacteria were determined by plating dilution series onto THY agar. The values are mean survival percentages ± SD (shown here in log scale) of six independent determinations from two independent cultures (CFU in the presence of H₂O₂ divided by the averaged CFU in the absence of H₂O₂). Student's t test: *, P < 0.05; **, P < 0.01; ***, P < 0.005.