Effects of ultraviolet radiation on the survival and metabolic and products of bacteroides melaninogenicus




Smith-Kappus, Sheryl

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Bacteroides melaninogenicus was determined to be an aerotolerant anaerobic bacterial species. It was shown that exposure to atmospheric air for up to 90 min does not affect the viability of these microorganisms. A growth curve constructed for the organism showed that after a 4 h lag growth phase, B. melaninogenicus reached stationary growth phase in just 3 h.

B. melaninogenicus was found to be more sensitive to chloramphenicol, metronidazole, and streptomycin than to any other antibiotic tested. Chloramphenicol, metronidazole, fluoroacetate, and caffeine, used in irradiation co-insult studies in this dissertation, were considered to be bacteriocidal and yet all allowed some cell viability even at the high superinhibitory concentrations tested.

In experiments investigating DNA repair, it was shown that B. melaninogenicus does not repair UV light induced damage via photoreactivation.

Survival curves constructed for the organism after exposure to UV light at 254 nm and 365 nm under aerobic and anaerobic conditions while the organisms were in exponential or stationary growth phase, revealed that the cells were most sensitive to UV induced damage when exposed to radiation while in the exponential growth phase under aerobic conditions at either wavelength. B. melaninogenicus exposed to UV light under anaerobic conditions while the cells were in stationary growth phase were much more sensitive to UV induced damage at 254 nm than cells irradiated under the same conditions at 365 nm UV.

Survival studies of B. melaninogenicus after co-insult with UV light and subinhibitory concentrations of chloramphenicol, metronidazole, caffeine, or fluoroacetate, at 254 nm UV or 365 nm UV, under aerobic and anaerobic atmospheric conditions illustrated a decreased shoulder region on the curves, particularly after 365 nm UV exposure, when compared to UV irradiation applied without subsequent chemical treatment.

The end products of the fermentation of glucose by B. melaninogenicus were affected after co-insult by UV and metronidazole, and UV and fluoroacetate. As expected, fluoroacetate treated cells produced less acetic acid, and in one mutant strain, SKF2r, small amounts of ethanol and methanol were produced. From the VPI strain, nine strains were isolated which produced altered metabolic end products from glucose; these mutants were named SKM1s, SKM2r, SKM3s, SKF1s, SKF2r, SKF3r, SKF4s, SKF5s, and SKF6s.



Ultraviolet Radiation , Bacteroides Melaninogenicus