Role of iron and superoxide for generation of hydroxyl radical, oxidative DNA lesions, and mutagenesis in Escherichia coli

We measured the generation of hydroxyl radical (OH.) and oxidative DNA lesi ons in aerobically grown Escherichia coli cells lacking in both superoxide dismutases (SodA SodB) and repressor of iron uptake (Fur) using electropara magnetic resonance and gas chromatography-mass spectrometry with a selected -ion monitoring method. A specific signal corresponding to OH. generation a nd an increase in oxidative DNA lesions such as 7,8-dihydro-8-oxoguanine an d 1,2-dihydro-2-oxoadenine were detected in the strain deficient in sodA so dB fur. We showed that iron metabolism deregulation in fur mutant produced a 2.5-fold iron overload. The sodA sodB fur strain was about 100-fold highe r mutability than the wild-type strain. The mutation spectrum in the strain was found to induce GC --> TA and AT --> CG transversions predominantly. T he hypermutability of the strain was suppressed by the tonB mutation which reduces iron transport. Thus, excess iron and excess superoxide were respon sible for OH. generation, oxidative DNA lesion formation, and hypermutabili ty in E. coli.