BOUND WATER, INOSITOL, AND THE EFFECT OF X-RAYS ON ESCHERICHIA COLI

Abstract

Aerosols of Escherichia coli B were subjected to 250 kv X-rays. It was found that maximal X-ray damage occurred at 70 to 80% relative humidity (R.H.). At these R.H. values only the water bound directly to cell macromolecules remains, and if the water layers were increased by using higher humidities, X-ray damage decreased. Also, at R.H. levels below 70% a sharp decrease in the sensitivity of the cells to the radiation occurred. Several chemicals known to protect cells against desiccation, ultraviolet, and X-ray damage were examined and of these i-inositol proved the most successful. The difference in the protective ability of these various compounds indicated that some protect cells against desiccation damage by retaining water, others by replacing bound-water molecules in macromolecular structure but those retaining water will not protect against X-rays. The results suggest that the physical removal or ionization of a strategic bound-water molecule by X-rays causes most of the cell deaths rather than ionizations occurring in the free water as the presence of the latter appears to offer cells a measure of protection.