Fig 3.

H₂O₂ inhibition zone assays. (A) H₂O₂ inhibition zone assay for DC3000, the catalase triple mutant, and its complemented strains. Representative pictures of the strains tested are shown. Below each picture is the diameter (cm) of the H₂O₂ inhibition zone ± standard deviation from three replicates. The catalase triple mutant is hypersensitive to H₂O₂. Complementation with KatB and KatG but not KatE significantly increased the tolerance of the catalase triple mutant to H₂O₂. (B) H₂O₂ inhibition zones for wild-type DC3000, the catalase single and double mutants, and their complemented strains ± standard deviations of three replicates. The loss of KatB or KatG resulted in an increased sensitivity to H₂O₂ in an additive fashion, indicating that these two catalases have nonredundant roles in protecting DC3000 from exogenous H₂O₂. The experiments were repeated four times with similar results.