FIGURE 2.

Salmonella lacking dksA are hypersusceptible to H₂O₂. A, survival of wild type (WT), dksA mutant, and dksA mutant complemented with a dksA gene expressed from the low copy vector pWDKS at various times after exposure to 100 μm H₂O₂. The initial counts of WT and dksA mutant at time 0 were ∼10⁵/well. B, killing activity of H₂O₂ against WT Salmonella compared with dksA, relA spoT (ppGpp°), and dksA ppGpp° mutants. The bacteria were grown for 20 h (stationary) or to an A_{600 nm} ∼0.5 (logarithmic). C, H₂O₂-consuming ability of Salmonella grown to stationary phase measured polarographically. The cultures were normalized to bacterial density as determined spectrophotometrically at A_{600 nm}. The data represent the mean percent survival ± S.E. (error bars) of 4–12 independent observations from at least two separate experiments. H₂O₂ consumption represents five independent observations from two separate experiments. *, p < 0.05; **, p < 0.01; ***, p < 0.001.