Fig. 2

Roles of four catalases (KatA1, KatA2, KatE, and KatMn), one alkyl hydroperoxidase (AhpC), and three glutathione peroxidases (Gpx1, Gpx2, and Gpx3) in the alleviation of exogenous hydrogen peroxide stress. Bars represent the average values from three independent experiments. Error bars represent the standard error of the mean. *, P < 0.001, significance calculated by Student’s t test. (a) Expression of H₂O₂-hydrolyzing enzyme genes in the strains KJ, KJΔKatA2, and KJΔAhpC after hydrogen peroxide challenge. The bacteria tested were treated with 2 mM H₂O₂ for 10 min before measuring katA1, katA2, katMn, katE, ahpC, gpx1, gpx2, and gpx3 transcription using qRT-PCR. All values were normalized to individual transcripts obtained from untreated KJ cells. (b) Regulatory role of OxyR in katA2 expression in response to exogenous H₂O₂ stress. The KJ and KJΔOxyR cells were untreated or treated with different H₂O₂ concentration as indicated for 10 min before measuring katA2 transcript using qRT-PCR. All values were normalized to katA2 transcript obtained from untreated KJ cells. (c) Regulatory role of OxyR in ahpC expression in response to exogenous H₂O₂ stress. The KJ and KJΔOxyR cells were untreated or treated with different H₂O₂ concentration as indicated for 10 min before measuring ahpC transcript using qRT-PCR. All values were normalized to ahpC transcript obtained from untreated KJ cells. (d) H₂O₂ susceptibility test of KJ and its derived isogenic mutants. The bacterial cell suspension tested was uniformly spread onto MH agar, and a sterile filter paper with 10 μl of 20% H₂O₂ was placed on the agar. After a 24-h incubation at 37 °C, the growth inhibition zone was measured