Determination of intracellular levels of ROS in wild type R. sphaeroides and the 2.4.1∆ oxyR mutant. Cultures were grown under normal iron (black) and iron-limiting (white) conditions in oxic and anoxic (-O2) environments. ROS generated by the cells were analysed after reaction with 10 mM 2,7-DCFH-DA. Cells incubated with 250 μM Paraquat (PQ) served as a positive control. The autofluorescence of cells without dye was subtracted from the measured values. The fluorescence intensity was normalised to the optical densities of the samples. The resulting values are presented in arbitrary units. The data represent the mean of three independent experiments, and the error bars indicate the standard deviation.