Fig. 5.

Ccp cannot protect the cytoplasm from exogenous H₂O₂. (A) Wild-type (MG1655), Δccp (MK416), Hpx⁻ (LC106), and Hpx⁻ Δccp (MK146) mutant cells were grown to OD₆₀₀ ∼0.1 and spread on a plate. Disks soaked in H₂O₂ were put on the plate, and the diameter of zone of inhibition was measured after 24 h. (B) Data from A are shown as bar graphs. (C) Modeling (SI Materials and Methods) shows that H₂O₂ exchange between the external environment and the periplasm is too fast for Ccp to significantly diminish the periplasmic H₂O₂ level. Therefore, Ccp has minimal effect on H₂O₂ entry into the cytoplasm. Steady-state fluxes (in %) are calculated relative to the rate of H₂O₂ entry into the periplasm. Asterisks represent statistical significance (*P ≤ 0.05; **P ≤ 0.01; ***P ≤ 0.001; ns, P > 0.05).