Effect of γ-Radiation on Escherichia coli grown in Deuterium Oxide Medium

Abstract

IT has been shown by several authors, for example by Alper and Gillies¹, that the nature of the growth medium has an effect on the radiation sensitivity of bacteria with regard to their ability to divide and form colonies. A simple, and yet considerable, change in the growth medium is the substitution of D₂O for H₂O. It was found that, on transferring cells from normal minimal medium (NH₄C1 2 gm., Na₂HPO₄ 6 gm., KH₂PO₄ 3 gm., NaCl 3 gm., MgCl₂ 10 mgm., Na₂SO₄ 26 mgm., glucose 5 gm. per litre) to the same made in 99.5 per cent D₂O, the cells grew, after a long lag period, with a generation time of 4 hr. at 37° C., which is about five times the normal. Similar results were found by Borek and Rittenberg². Such cells, after growth, must possess very considerable substitution of deuterium for hydrogen, with consequent modification of hydrogen-bonded molecular structures as well as any changes due to the increased rotational moment of inertia of water. The greatly reduced rate of division could be due to slowed enzyme kinetics, to less efficient protein synthesis, or to some modification in the DNA, among other reasons. Since it is likely that radiation action, as regards cell division, is concerned with the DNA or its organization, it seemed of interest to see whether cells grown in D₂O showed any differences in radiation sensitivity.