Graduate Thesis Or Dissertation
 

The site of action of radio-lethal compounds on Micrococcus radiodurans

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  • Iodoacetic acid and diphenylamine were used in this study to elucidate the mechanisms of resistance of Micrococcus radiodurans to radiation. This organism, a gram positive, non-spore forming, salmon-pink, tetracoccus has a LD₅₀ of 213,000 R when grown in the absence of radio-modifying agents. M. radiodurans, when grown in media containing iodoacetic acid, was more resistant to ultraviolet light, but its LD₅₀ for X-rays was not changed. The presence of diphenylamine in the growth media did not alter the sensitivity to ultraviolet light, but did reduce the LD₅₀ for X-rays to 134,000 R. The effect of diphenylamine and iodoacetic acid upon the colored carotenoid composition was analyzed by thin layer chromatography. Cells grown in the absence of radio-modifiers possessed seven pigment bands. Cells grown in the presence of iodoacetic acid demonstrated an increase in pigment band number one, but lacked pigment components number six and seven. Diphenylamine did not alter the colored carotenoid composition of M. radiodurans. Thin layer chromatography was used to monitor the effect of radio-modifying agents on extractable lipid composition of M. radiodurans Iodoacetic acid did not change the extractable lipids of this microorganism. Cells incubated in the presence of diphenylamine had an additional lipid band, as well as larger amounts of fatty acids. Gas liquid chromatography was used to examine the fatty acid composition of M. radiodurans. Cells grown in the presence of iodoacetic acid possessed two compounds not found in the other cells. Diphenylamine increased the saturated: unsaturated C-16 fatty acid ratio by approximately three fold. The results indicate that there is a relationship between the carotenoid pigments and the resistance of the test organism to ultraviolet light, but not to X- and gamma rays. In addition, it appears that the unsaturated lipids, in particular C-16, protect M. radio-durans from the harmful effects of X- and gamma rays. There was no correlation between fatty acid content and ultraviolet light sensitivity.
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