A ΔsrrAB strain is deficient in growth upon H2O2 challenge and has decreased transcription of ahpC and kat during aerobic growth.
Panels A-B; A ΔsrrAB strain is deficient in growth upon H2O2 challenge. The WT (JMB1100) with pCM28 empty vector (pEV) and the ΔsrrAB strain (JMB1467) with pCM28 (pEV) or psrrAB were diluted into defined medium to a final optical density of 0.025 (A600) and challenged with vehicle control (Panel A) or 1.32 mM hydrogen peroxide (H2O2) (Panel B) at the point of inoculation (indicated by arrow). Panel C; Catalase (Kat) activity is decreased in a ΔsrrAB strain. Kat activity was assessed in cell-free lysates from the WT, ΔsrrAB, ΔperR (JMB2151), and Δkat (JMB2078) strains. ND represents no detectable activity. Panel D; Superoxide dismutase (Sod) activity is not decreased in a ΔsrrAB strain. Sod activity was assessed in cell-free lysates from the WT, ΔsrrAB, sodA::Tn (JMB 6326), and sodM::Tn (JMB 2968) strains. Panel E; The abundances of mRNA transcripts corresponding to genes that encode for H2O2 detoxification proteins are lower in the ΔsrrAB strain. The abundances of the ahpC, kat, cydB and spa transcripts were determined in the WT and ΔsrrAB strains. The data were normalized to 16s rRNA transcript levels and are presented as fold-change relative to the WT. Representative data are shown in Panels A-B and experiments were repeated on three independent occasions. Data in Panel C-E represent the average of biological triplicates with standard deviations shown. Where indicated, two-tail student t-tests were performed on the data and * represents statistically significant data with P< 0.05.