FIG 5.

H₂S induces the OxyR-mediated stress response. (A) CAT staining analysis. Cells were harvested just prior to (−) and 30 min after the addition of 0.25 mM H₂S or 0.1 mM H₂O₂ (top). Protein samples of ∼10 μg from the cell lysates indicated were separated by native PAGE and stained for CAT activity. The ΔkatB and ΔoxyR mutant strains (constitutive high-level expression) were used as negative and positive controls. In the analysis shown at the bottom, various concentrations of H₂S were examined for the ability to induce expression of the katB gene. (B) Impact of H₂S on the expression of four members of the OxyR regulon. β-Galactosidase assays were carried out with lacZ reporter vectors. Cells grown to mid-log phase were treated with the chemicals indicated for 30 min and then harvested for the assays. Concentrations: H₂S, 0.25 mM; H₂O₂, 0.2 mM; dipyridyl (Dip), 0.25 mM. β-Galactosidase activities are reported as the mean ± SD (n = 4). Similar results were obtained by qRT-PCR assay (see Fig. S3 in the supplemental material).