Fig. 4: Determining whether hydroxyl and/or superoxide radicals are formed.

a Survival curves of stationary phase cells incubated with 100 µM valinomycin (val) in the presence of either the iron chelators ferrozine (Fer, 500 µM) or 2,2’-Bipyridyl (Bip, 500 µM). Data reflect mean ± SD of three biological replicates. b Survival curves of stationary phase cells incubated with 100 µM valinomycin (val) in the presence of either the hydroxyl radical scavenger thiourea (TU, 150 mM) or the superoxide scavenger tiron (Tiron, 10 mM). Data reflect mean ± SD of three biological replicates. c Survival curves of stationary phase ΔkatA and ΔsodA cells incubated with 100 µM valinomycin (val). katA and sodA code for the main catalase and superoxide dismutase, respectively. The viable counts of cells in the presence of 1 % DMSO were similar to that of wild type cells and are not indicated. Data shown reflect mean ± SD of three biological replicates. d ROS production in stationary phase wt and ΔsodA cells after 4 h incubation with 100 µM valinomycin (val) measured by the fluorescent ROS probe H2DCFDA. Control cells were treated with either 1 mM paraquat or 1 % DMSO for 4 h. The fluorescence intensities of 120 cells were measured microscopically and plotted.