FIG 7.

Unregulated import of iron into NTHI strain 86-028NP exacerbates the effects of H₂O₂-induced killing. The genes encoding catalase (hktE) (A), peroxiredoxin glutaredoxin (pgdX) (B), or the ferritin-like protein Dps (dps) (C) were deleted in a strain of 86-028NP that lacked the ferric uptake regulator, Fur. All strains were grown exponentially and then treated with 500 μM H₂O₂ for 10 min. The cells were harvested and plated to assess viability. (A, B) Loss of the ability to decompose H₂O₂ in the face of unrestricted iron import produced significant losses in cell viability relative to that of the parent strain or the respective single mutant strain. (C) Loss of the ability to bind iron in the dps mutant produced a nearly total loss of cell viability when iron import was unregulated and the cells were treated with H₂O₂. Complementation of the double mutants with hktE, pgdX, or dps restored cell viability. Significance was calculated relative to the results for the parent strain. Error bars show standard errors of the means. *, P ≤ 0.05; **, P ≤ 0.01; ***, P ≤ 0.001; ****, P ≤ 0.0001 (n = 3 [A]; n = 4 [B, C]).