Radiosensitization of Pseudomonas radiora O-1 by N 2 O in Aqueous Suspension

Abstract

The radiosensitizing action of N/sub 2/O toward a radioresistant bacterium, Pseudomonas radiora O-1, was investigated in dilute suspension. The radiosensitivity of P. radiora O-1 in N/sub 2/O-saturated suspension was 2.9 times higher than that in N/sub 2/-saturated suspension, but less than that in O/sub 2/-saturated suspension. The addition of several OH radical scavengers to N/sub 2/O suspension decreased the sensitizing effect of N/sub 2/O, indicating that OH radicals are responsible for the sensitization by N/sub 2/O. This sensitization was further prevented by adding catalase and peroxidase, which can destroy H/sub 2/O/sub 2/, while heat-denatured catalase was without effect. In addition, the number of viable cells did not change even when the cells were incubated in 0.1 mM H/sub 2/O/sub 2/ suspension at 0/sup o/C. These results indicate that the sensitization by N/sub 2/O is due to the cooperative action of OH radical and H/sub 2/O/sub 2/ that allowed H/sub 2/O/sub 2/ to sensitize only when OH radicals were present. The radiosensitivity in N/sub 2/O/O/sub 2/ gas mixture is twice that in O/sub 2/ and is decreased by adding ethanol, but it is not affected by addition of catalase. Since in this gas mixture all hydrated electrons are scavenged by N/submore » 2/O rather than by O/sub 2/, this indicates that molecular O/sub 2/ is more effective than H/sub 2/O/sub 2/ on the interaction with the radical sites produced by OH attack.« less