FIG 4.

Cells of EGD-e (A) and 10403S (B) (WT and ΔsigB mutant) grown aerobically at 37°C until the mid-exponential phase of growth and then challenged with 1% (A) and 0.43% (B) H₂O₂. D.L. denotes the detection limit, and the asterisks denote a difference with statistical significance (P < 0.05). Catalase tests were performed in triplicate (one representative experiment is shown), with the addition of 100 μl of 30% H₂O₂ solution in 5 ml of culture. Cultures for catalase tests were grown under conditions similar to those used in challenge tests. The error bars represent the standard deviations.