Comparative Molecular Analysis of Genes for Polycyclic Aromatic Hydrocarbon Degradation

Abstract

Aromatic hydrocarbons are found ubiquitously in nature. Their sources vary from biosynthesis de novo by organisms to abiotic reactions on naturally-occurring carbon deposits to chemical synthesis by man. It is generally accepted, however, that the bulk of aromatic compounds found in the environment are not of biosynthetic origin but are produced through the pyrolysis of organic materials such as the amorphous polymer lignin. Unsubstituted aromatic hydrocarbons are generally formed at high temperatures (2000°C) of pyrolysis. Intermediate temperatures of pyrolysis (400–800°C) result in the formation of alkylsubstituted aromatic hydrocarbons together with unsubstituted aromatic compounds. In contrast, petroleum is formed at low temperatures (80–150°C) and contains aromatic hydrocarbons with two or three alkyl substituents as the major components (1). The ubiquitous presence of aromatic hydrocarbons in the environment is generally thought to result from the deposition of airborne particles that contain combustion products (2,3). In addition to the abiotic source of aromatic compounds, there is little doubt that the rapid industrialization over the last century has increased the deposition of man-made aromatic hydrocarbons into the environment. Environmental contamination by anthropogenic sources results from the isolation, processing, combustion and disposal of fossil fuel. The production of value-added petroleum products such as polymers, plastics, pesticides, solvents, explosives and even pharmaceuticals can lead to release of aromatic hydrocarbons into the environment.