FIG 1.
Endogenous H2S does not protect bacteria against H2O2. (A) H2S production in various S. oneidensis strains. Lead acetate-soaked paper strips show a brown or black PbS stain as a result of reaction with H2S under aerobic conditions. The relative H2S levels shown were obtained by normalization to the average level of the wild type (WT), which was set to 100%. The Δtriple (ΔmdeA ΔSO1095 ΔsseA) mutant strain lacks the ability to produce H2S via cysteine metabolism, while the Δpenta mutant strain carries additional deletions in the psrA and sirA genes, thus removing the ability to produce H2S through respiration. (B) H2O2 sensitivity assay. Paper disks of 6 mm loaded with 10 μl of 5 M H2O2 were placed on a bacterial lawn and photographed after 16 h at 30°C. The relative H2O2 susceptibilities shown were obtained by normalization to the average level of the wild type, which was set to 100%. The ΔcysKC mutant is a complemented mutant carrying a copy of the cysK gene integrated into the chromosome and produces H2S like the wild type. (C) H2O2 consumption assay. H2O2 at 0.5 mM was added to mid-log-phase cultures (OD600 of ∼0.2, the same afterward), and the H2O2 remaining at the time points indicated was measured. (D) Survival assay. One millimolar H2O2 was added to mid-log-phase cultures. After 5 and 30 min, samples were diluted and plated on LB. Colony counting was done after 24 h. For panels A and B, experiments were performed five times and representative results are shown. In panels B and D, data are reported as the mean ± SD (n = 4).