Figure 7. Catalase activity and hydrogen peroxide resistance in the XackatE mutant.

(A) Xac wild-type (WT), XackatE (katE⁻) and cXackatE (ckatE) strains were grown aerobically in SB medium to early exponential (EE, 4 h) and stationary (S, 24 h) phases, and soluble extracts were prepared as described in Materials and Methods . Equal amounts of protein (25 µg) were separated by 8% non-denaturing PAGE and stained for catalase activity by the method of Scandalios [19]. (B) Cells in early exponential (EE) or stationary (S) phase of growth were exposed to the indicated concentrations of H₂O₂ for 15 min. The number of CFU was determined for each culture before and after the peroxide treatment by plating of appropriate dilutions. The percentage of survival is defined as the number of CFU after treatment divided by the number of CFU prior to treatment ×100. Data are expressed as the mean ± standard deviation of three independent experiments.