Radiation sensitization of bacteria and bacterial spores by nitrous oxide and low concentrations of oxygen: evidence for a common mechanism of damage

Experiments were made with B. megaterium and E. coli to measure the radiation sensitivity of bacteria and bacterial spores to 260 kVp X-rays while the cells were equilibrated with one of four gases (100% N2, air, 0.8% O2, or 100% N2O). In addition, measurements were made of the radiosensitivity in these gases when different additives (or combinations of additives) were present. t-Amyl alcohol, histidine, catalase, and SOD were the additives tested. With both organisms, none of the additives altered the response in N2 or in air. In contrast, all of the additives (except the H-I enzymes) reduced the responses in N2O and 0.8% O2. For both organisms, each of the additives reduced the response to the same level. Tests for an additivity in the protective effects of these agents showed no greater amount of protection than either additive could have achieved alone. The results, presented in tabular form, provide evidence that O2- is an important intermediate in radiation-induced sensitization by both N2O and low concentrations of O2. (U.K.)