Search for an Effect of Oxygen on the Direct X-ray Inactivation of Bacteriophage

Abstract

A B. coli phage has been irradiated with X rays in broth which contained sufficient protein to suppress the indirect effect due to ionization in the water. Therefore, inactivation of the phage was due to the direct effect of the radiation on the phage particles, to which Lea's theory (1946) ought to apply. One phage suspension contained 10 to 15 ml./litre of dissolved oxygen, and a second zero. The activity of each suspension diminished exponentially with increase in the X-ray dose. If the oxygen did increase the sensitivity of the phage at all it was unlikely to have been by more than 10 per cent. The mean diameter of the phage particle, deduced from the 37 per cent. inactivation dose and Lea's theory, was 54 millimicrons. Other methods have given values of 45 and 75 millimicrons for the same phage. Broth, without phage, containing the normal amount of dissolved oxygen, was given the maximum dose used previously, and then the phage particles were added immediately after the end of the irradiation. No inactivation was detected. No modification of Lea's theory is necessary as a consequence of this experiment.