MICROBIAL DEGRADATION OF POLYCYCLIC AROMATIC HYDROCARBON MIXTURES

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Many environments are exposed to polycyclic aromatic hydrocarbons (PAHs) and N-heterocyclic aromatics (NHAs) as complex mixtures. Specifically, 3000 former sites of coal gasification plants constitute major health hazards. The research will build upon the progress made in a) the isolation of soil microorganisms and consortia of microorganisms that degrade polyaromatic compounds and mixtures thereof, b) the characterization of the metabolic intermediates that are produced by known cultures, new isolates and consortia c) the effects of soil constituents on the bioavailability and sorption of these compounds, and d) the genotoxic effects of these compounds. This proposal targets the recalcitrant, carcinogenic 4 and 5 ring polycyclic hydrocarbons (PAHs) and the equally important N-heterocyclic aromatics (NHA). Our overall objective is to determine and enhance the microbial degradation rates of polyaromatics under simulated environmental conditions and to decrease potential health hazards associated with the PAH and NHA biodegradation products. The goal is to improve upon biodegradation and mineralization for the elimination of polyaromatic compounds and their metabolites from polluted soils. The specific aims: 1) Isolate organisms that degrade the multi-ring PAHs and NHAs from gasification sites under study using analog enrichment techniques. Compounds include further studies with BaP, benz(a)anthracene, dibenzo(c,g)carbazole, dibenz(a,j)acridine and new initiatives with chrysene and four ring acridine and carbazole derivatives. 2) Use isolated degraders of 2, 3 and 4 ring compounds singly, in mixtures as well as in contaminated soils. Metabolic intermediates, ring cleavage and reaction sequences will be investigated using both isolates and pure cultures. Studies using algae and bacteria in a cometabolic fashion to degrade large ring PAHs will also be undertaken. 3) Determine the impact of carcinogenic metals on the biodegradation of PAHs by isolated 2, 3 and 4 ring degraders. 4) Determine the extent that 2, 3, and 4 ring degrader isolates further degrade stable biodegradation products, and photooxidized products, of PAH/NHA in incubations that mimic preexposure conditions. 5) Test for the capacity of stable intermediates of biodegradation and photooxidation to induce cytogenic damage in proliferating human lymphocytes as measured by induction of micronuclei. 6) Examine the health benefit of biodegradation. This will involve determining the mutagenic activities of soil organic extracts before and after reintroduction of PAH metabolite mixtures and individual degradation products. With an understanding of the microbial hydrocarbon degradation process, strategies will be developed for utilizing microbial hydrocarbon degrading activities for the removal of toxic and carcinogenic PAHs and NHAs and their intermediates from contaminated ecosystems.