Membrane damage can be a significant factor in the inactivation of Escherichia coli by near-ultraviolet radiation

A DNA repair competent strain of Escherichia coli K-12 showed sensitivity to inorganic salts (at concentrations routinely used in minimal media) after irradiation with broad spectrum near-UV radiation, at fluences that caused little inactivation when plated on complex growth medium. This effect was not observed with cells that had been exposed to 254 nm radiation. This sensitivity to minimal medium was increased by increasing the salt concentration of the medium and by increasing the pH of the medium. This sensitivity was greatly increased by adding to the medium a low concentration of commercial glassware cleaning detergent that had no effect on unirradiated cells or far-UV irradiated cells. These findings may explain the large variability often observed in near-UV radiation survival data, and demonstrate that, at least on minimal medium plates, membrane damage contributes significantly towards cell killing. This phenomenon is largely oxygen dependent. (author)