FIG 3.

A strain of 86-028NP that lacks the peroxidase PgdX has an increased ability to decompose H₂O₂. Strains of 86-028NP that lacked the genes encoding the catalase HktE, the peroxidase PgdX, or both HktE and PgdX were grown exponentially and then treated with (+) 500 μM H₂O₂ for 30 min. A control sample was left untreated (−). The cells were harvested and lysed, and their ability to decompose H₂O₂ assessed using an Amplex red catalase assay kit. The addition of H₂O₂ to the cells produced increased H₂O₂ decomposition activity in the parent strain relative to the activity in the untreated cells. The hktE mutant showed a large reduction in H₂O₂ decomposition activity. In contrast, the pgdX mutant demonstrated H₂O₂ decomposition activity that was significantly greater than that of the parent. Slight activity remained in the strain that lacked both hktE and pgdX. Error bars show standard errors of the means. ***, P ≤ 0.001; ****, P ≤ 0.0001 (n = 8).