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

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Abstract
An Escherichia coli phage was 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 10-15 ml./1. of dissolved O2, and a second contained none. The activity of each suspension diminished exponentially with increase in the X-ray dose. If the O2 did increase the sensitivity of the phage at all, it was unlikely to have been more than 10%. The mean diam. of the phage particle, deduced from the 37% inactivation dose and Lea''s theory, was 54 mu. Other methods have given values of 45 and 75 mu for the same phage. Broth, without phage, containing the normal amt. of dissolved O2, was given the max. 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 expt.

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