Pretreatment of Escherichia coli cultures with the iron chelator 2,2’-dipyridyl (1 mM) protects against the lethal effects of low concentrations of hydrogen peroxide (<15 mM). However, at H2O2 concentrations equal to or greater than 15 mM, dipyridyl pretreatment increases lethality and mutagenesis, which is attributed to the formation of different types of DNA lesions. We show here that pretreatment with dipyridyl (1 mM) prior to challenge with high H2O2 concentrations (≥15 mM) induced mainly G:C→A:T transitions (more than 100X with 15 mM and more than 250X with 20 mM over the spontaneous mutagenesis rate) in E. coli. In contrast, high H2O2 concentrations in the absence of dipyridyl preferentially induced A:T→T:A transversions (more than 1800X and more than 300X over spontaneous mutagenesis for 15 and 20 mM, respectively). We also show that in the fpg nth double mutant, the rpoB gene mutation (RifS-RifR) induced by 20 mM H2O2 alone (20X higher) was increased in 20 mM H2O2 and dipyridyl-treated cultures (110X higher), suggesting additional and/or different lesions in cells treated with H2O2 under iron deprivation. It is suggested that, upon iron deprivation, cytosine may be the main damaged base and the origin of the pre-mutagenic lesions induced by H2O2.
Hydrogen peroxide; Dipyridyl; Mutagenesis; Iron; Fenton reaction
