Fig. 5

Effects of visible light and hydrogen peroxide (H₂O₂) on the MR-1ΔhemH1ΔhemH2 mutant. a Effects of hydrogen peroxide (H₂O₂) addition on the growth of the MR-1ΔhemH1ΔhemH2 mutant. The MR-1 wild type strain, the hemH1, the hemH2 in-frame deletion mutants and the hemH1-hemH2 double mutant strain were grown in LB broth containing 0, 0.1, 0.3, 0.5, 0.7 and 1 mM of hydrogen peroxide and incubated at 28 °C for 18 h. Different concentrations (0, 0.1, 1, 10 μg/ml) of hemin didn’t rescue the growth rate of the hemH1-hemH2 double mutant, when these strains were grown in the LB broth containing 0, 0.1, 0.3, 0.5, 0.7 and 1 mM of hydrogen peroxide and incubated at 28 °C for 18 h; b Effects of visible light on the growth of the MR-1ΔhemH1ΔhemH2 mutant. Cell colonies grown from a droplet of mid-log-phase culture (OD₆₀₀ of ~ 0.2) for each indicated strain on LB plates (supplemented with 10 μg/ml of hemin and 15 μg/ml gentamycin). Experiments were conducted under visible light (about 700~1,000 lx) and dark condition on LB plates. The wild type MR-1 carrying the empty vector was used as control, the double deletion mutant MR-1ΔhemH1ΔhemH2 contained the empty vector, pHERD30T-hemH1 and pHERD30T-hemH2, respectively, were compared. Different concentrations of supplement hemin failed to rescue the phenotype and the growth rate of the hemH1-hemH2 double mutant, when these strains were grown in the LB broth containing 0, 0.1, 1, 10, 100 μg/ml of hemin and incubated at 28 °C for 18 h; c The KatB-dependent peroxidase activity assays of MR-1 and the double mutant MR-1ΔhemH1ΔhemH2