Microbial Metabolism of Polycyclic Aromatic Hydrocarbons

Abstract

Publisher Summary This chapter deals with the microbial transformation of polycyclic aromatic hydrocarbons (PAHs). The similarities and differences between the microbial and mammalian metabolism are described. Bacteria, filamentous fungi, yeasts, cyanobacteria, diatoms, and other eukaryotic algae have the enzymatic capacity to oxidize PAHs that range in size from naphthalene to benzo[ a ]pyrene. The hydroxylation of PAHs always involves the incorporation of molecular oxygen; however, there are differences in the mechanism of hydroxylation of PAHs by prokaryotic and eukaryotic microorganisms. Bacteria oxygenate PAHs to form a dihydrodiol with a cis configuration. The genes for the initial oxidation of PAHs are localized on plasmids. In contrast to bacteria, fungi oxidize PAHs via a cytochrome P-450 monooxygenase to form arene oxide, which can isomerize to phenols or undergo enzymatic hydration to yield trans-dihydrodiols. Multiple oxidative pathways may be involved in the cyanobacterial metabolism of PAHs. Studies on PAH metabolism are entering a new era; biochemical genetic techniques such as gene cloning and transposon mutagenesis will provide new insight into the biochemistry and regulation of PAH degradative pathways.