FIG 6.

Iron ions facilitate degradation of H₂O₂ by living cells. (A) Cells of the indicated strains grown overnight on LB plates with or without the indicated additives were collected with a metal loop, washed, and suspended to an OD₆₀₀ of ∼0.1. Five minutes after the addition of 0.5 mM H₂O₂, the remaining H₂O₂ was determined. Con, initial concentration; −, LB without additive; LC, living cell; DC, disrupted cell. Asterisks indicate statistically significant differences (*, P < 0.05; **, P < 0.01; ***, P < 0.001). Error bars indicate SD (n = 4). (B) Effects of indicated mutations on the plating defect on LB plates without or with 2 mM Fe²⁺. (C) Expression of ahp and katB in the indicated strains under indicated conditions. Cells grown on the LB plates without or with 2 mM Fe²⁺ for 16 h were collected, washed, and resuspended in PBS. Aliquots were treated with 200 μM H₂O₂ for 10 min, and ahp and katB promoter activities assayed using an integrative lacZ reporter.