Modification of the Radiation Sensitivity of Bacteriophage T7 by O₂ and N₂O

Summary

The radiation sensitivity of T7 suspensions is strongly dependent on chemical additives. We have compared the response to x-irradiation in the presence of 100 per cent N₂, 100 per cent O₂ (e_aq⁻ and H· scavenger) and 100 per cent N₂O an e_aq⁻(scavenger that increases ^·OH concentration), in the presence of a 10⁻² dilution of medium and a 10⁻⁵ dilution (equivalent to medium free).

Survival curves are frequently multicomponent, with sharp break points, and radiation sensitivity must be measured at varying dosage levels. In the 10⁻³ dilution, the order of radiation sensitivity at low doses is, k_L = N₂ > N₂O > O₂, and at high doses, k_H = O₂ ≅ N₂O > N₂. In the 10⁻⁵ dilution, or medium free, the order at low doses is k_L = N₂O > N₂ ≅ O₂ with k_H difficult to define.

It is concluded: (1) the OH radical is an important damaging species for T7, and (2) ‘O₂ protection’ is an experimental artifact associated with impurities in the suspension.