Significance of pigments in radiation resistance of Micrococcus radiodurans Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/pn89db02r

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  • An ecological study of a microorganism similar to that isolated in 1956 and designated as Micrococcus radiodurans indicated that the organism could be isolated from several different environments. By taking advantage of its radio-resistivity, high levels of gamma radiation were used in the isolation procedures to inactivate most of the non-resistant microflora. By this means, microorganisms resembling M. radiodurans were isolated from ground beef and pork sausage as well as from beef hides and water from Cox Creek (Albany Oregon). Similar organisms could not be isolated, however, from soil, hay or fecal material. All of the environments tested were in the vicinity of the Nebergall Packing Plant, Albany, Oregon. Pre-incubation and pre-inoculation experiments indicated that M. radiodurans did not compete well with the natural micro-flora present in meat and soil samples. The use of enrichment culture techniques and incubation of the samples before irradiation did not facilitate the isolation of M. radiodurans. The presence of NZ-Case (a tryptic digest of casein) in the isolation medium produced more luxuriant growth than TGYM medium but the radiation sensitivity of M. radiodurans increased ten-fold in the former medium and the degree of pigmentation was less. Subsequent studies using thin layer chromatography indicated that the less resistant strain was lacking two of the eight pigments present in the more resistant culture. The degree of resistance was inversely related to the concentration of NZ-Case in the growth medium at all of the levels tested. At the highest level of NZ-Case used (0.5 percent), the LD₅₀ dose was 350 k rads as compared to 700 k rads when TGYM was the growth medium. The resistance to ultraviolet radiation was also reduced. Removal of NZ-Case from the growth medium resulted in a return of the high level of resistance and the reappearance of the missing pigments. A possible role of the pigments in the radiation resistance of this organism was thus suggested and described. In this role the pigments would serve as scavengers of toxic ions and radicals produced by radiation and thus protect the functionally important lipids and lipoproteins of the cell membranes from being altered with resultant release of cellular enzymes. Spectral analysis of the eight pigments indicated that they were all closely related and were tentatively identified as lycopene, hydroxy lycopene or di-hydroxy lycopene. None of the pigments absorbed in the ultraviolet range. Pigments obtained from cells grown in NZ broth had the same spectral characteristics but were present in reduced concentrations.
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