| Cometabolic biodegradation processes are potentially useful for the bioremediation of hazardous waste sites. In this study the potential application of phenol-oxidizing and nitrifying bacteria as "priming biocatalysts" was examined in the degradation of polycyclic aromatic hydrocarbons (PAHs), aryl ethers, and aromatic ethers. We observed that a phenol-oxidizing Pseudomonas strain cometabolically degrades a range of 2-and 3-ringed PAHs. A sequencing batch reactor (SBR) was used to overcome the competitive effects between two substrates and the SBR was evaluated as a alternative technology to treat mixed contaminants including phenol and PAHs. We also have demonstrated that the nitrifying bacterium Nitrosomonas europaea can cometabolically degrade a wide range polycyclic aromatic hydrocarbons (PAHs), aryl ethers and aromatic ethers including naphthalene, acenaphthene, diphenyl ether, dibenzofuran, dibenzo-p-dioxin, and anisole. Our results indicated that all the compounds are transformed by N. europaea and that several unusual reactions are involved in these reactions. In the case of naphthalene oxidation, N. europaea generated predominantly 2-naphthol whereas other monooxygenases generate 1-naphthol as the major product. In the case of dibenzofuran oxidation, 3-hydroxydibenzofuran initially accumulated in the reaction medium and was then further transformed to 3-hydroxy nitrodibenzofuran in a pH- and nitrite-dependent abiotic reaction. A similar abiotic transformation reaction also was observed with other hydroxylated aryl ethers and PAHs. We also characterized the role of AMO in the degradation of aromatic ethers. Our results indicated that aromatic ethers including anisole were transformed by both O-dealkylation or hydroxylation reactions. This research has led to the development of a rapid colorimetric assay to detect AMO activity. |
