Radiation-induced damage in Escherichia coli B: The effect of superoxide radicals and molecular oxygen

The roles of superoxide radicals and of molecular oxygen in the radiodamage of Escherichia coli B suspended in dilute phosphate buffer have been studied. The presence of high concentrations of polyethylene glycol in the γ-irradiated cell suspensions had no effect on bacterial radiosensitivity. This indicates that the damage was primarily endogenous, i.e., originated intracellularly. Saturation of the cell suspensions with N₂O doubles the radiosensitivity, thus indicating that OH radicals are responsible for the majority of the damage (indirect radiation effect). The presence of oxygen either in the absence or presence of N₂O brings about roughly a threefold increase in the radiosensitivity. Since in the presence of N₃O all e(aq)^- are scavenged by the nitrous oxide rather than by oxygen, this shows that superoxide radicals play no role in the bacterial radiodamage. Our results substantiate the attribution of the oxygen effect to a direct interaction of O₂ with the OH-damaged sites on vital biomolecules and exclude any significant contribution of e(aq)^- and O₂^- to the cellular radiodamage.