Studies on the Radiation Inactivation of Microorganisms: VII. Nature of the X-Ray-Induced Breakdown of Deoxyribonucleic Acid in Haemophilus influenzae

X rays induce a vigorous DNA breakdown in logarithmic growth phase cells of Haemophilus influenzae and the effect is inhibited by high concentrations of citrate, suggesting the action of a DNase.

Abstract

X rays induce a vigorous DNA breakdown in logarithmic growth phase cells of Haemophilus influenzae. The effect is inhibited by high concentrations of citrate, suggesting the action of a DNase. The x-ray dose giving maximal effect was tco small either to produce a direct split in a hypothetical DNase-inhibitor complex or to produce holes in a hypothetical membrane, which keeps the DNase separated from the cell DNA. It is argued that the DNase activation is one of the secondary x ray effects resulting from disorganization within the cell. Cysteamine or removal of oxygen from the cell suspension protected against both killing of the cells and induction of DNA breakdown.