EFFECTS OF NEAR-ULTRAVIOLET IRRADIATION ON GROWTH AND OXIDATIVE METABOLISM OF BACTERIA

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Abstract
The effects of irradiation with near-ultraviolet light (360 mu) have been studied with Escherichia coli W and a strain of Pseudomonas aeruginosa. The growth of the aerobe P. aeruginosa was inhibited by light on minimal salts media containing succinate, glutamate or glucose as sole carbon sources. The facultative anaerobe E. coli was capable of growth under irradiation on a fermentable carbon source such as glucose-but with a smaller yield of cells on limiting substrate as compared to unirradiated control cultures. The rate of growth of aerobic irradiated cells on glucose was equal to that of anaerobic growth on that carbon source, and there was a greater accumulation of end products of glucose catabolism aerobically in the light as compared to dark controls. When irradiated in media containing carbon sources from which energy was obtainable only by oxidative phosphorylation (such as succinate or malate), E. coli cells were still capable of oxidizing these substrates but could not grow on them. This bacterio-static effect of 360-m[mu] light could be reversed by the addition of glucose which resulted in the growth of irradiated cells. Visible (400 to 600 m[mu]) light was found to have no effect. Irradiated E. coli cells in succinate were found to contain no naphtho- or benzoquinones (compounds which are more sensitive to 360-mu irradiation than other components of the respiratory chain). It is suggested that the effect of 360 m[mu] light on whole cells is the destruction of light-sensitive components, (such as the benzoquinone Q8 and naphthoquinone K2C45) of E. coli W which are essential for obtaining energy from oxidative metabolism.