Graduate Thesis Or Dissertation
 

An evaluation of benzo(a)pyrene metabolism in an oyster (Ostrea edulis)-bacteria system

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  • The overall objective of this research project was to evaluate the metabolism of benzo(a)pyrene (BaP) by the European flat oyster (Ostrea edulis)-bacteria system. Individual oysters exist in nature as "systems" with commensal microorganisms and should be recognized as such when the metabolism of a specific environmental contaminant is being studied. Since bivalves are exposed to environmental pollutants that enter coastal waters, it is important to determine if the "natural" oyster system can detoxify those contaminants likely to cause biological damage. Tritiated-BaP was incubated with whole animal multienzyme preparations of (1) oyster/bacteria and (2) bacteria-free oyster. Background controls were run with homogenizing buffer (no oyster tissue added), homogenizing buffer + antibiotics (no oyster tissue added) and autoclaved oyster/bacteria multienzyme systems. Extraction techniques allowed separation of four fractions: (1) unmodified ³H-BaP plus simple non-conjugated derivatives; (2) ³H-BaP - glucuronides and -sulfates; (3) other ³H-BaP polar derivatives susceptible to cleavage by base/acid hydrolysis; and (4) the remaining ³H-BaP derivatives tightly bound and unaffected by previous treatment. Further separation of the unaltered ³H-BaP and the simple non-conjugated derivatives was effected by thin-layer chromatography. The results show a metabolic conversion of ³H-BaP by both multienzyme systems to simple, non-conjugated ³H-BaP derivatives and to other more polar ³H-BaP derivatives which were not susceptible to cleavage by glucuronidase/sulfatase or hydrolysis treatment. Hydrolysis-susceptible ³H-BaP metabolites were detected in the oyster/bacteria multienzyme preparations. Thus, it was not possible to clearly distinguish the metabolism of BaP by bacterial multienzymes from that of oyster multienzymes, but it does appear that the major proportion were contributed by oyster multienzymes. There were several additional points of interest. The treatment of oysters with antibiotics prior to and during the ³H-BaP incubation eliminates their indigenous bacterial flora as established by most-probable-number analyses of bacterial numbers. Further studies are required to determine whether or not metabolic conversions are due to the presence of bacterial cell-free enzymes. Also, the importance of establishing a background measure by an inviable enzyme incubation with the substrate is deemed critical as a result of this study. Finally, two oxidative degradation products are formed during the stustrate incubation, the subsequent organic extraction and/or the TLC preparation.
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