The intent of this review is to provide an outline of the microbial degradation of polycyclic aromatic hydrocarbons. A catabolically diverse microbial community, consisting of bacteria, fungi and algae, metabolizes aromatic compounds. Molecular oxygen is essential for the initial hydroxylation of polycyclic aromatic hydrocarbons by microorganisms. In contrast to bacteria, filamentous fungi use hydroxylation as a prelude to detoxification rather than to catabolism and assimilation. The biochemical principles underlying the degradation of polycyclic aromatic hydrocarbons are examined in some detail. The pathways of polycyclic aromatic hydrocarbon catabolism are discussed. Studies are presented on the relationship between the chemical structure of the polycyclic aromatic hydrocarbon and the rate of polycyclic aromatic hydrocarbon biodegradation in aquatic and terrestrial ecosystems.

Biodegradation of polycyclic aromatic hydrocarbons

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

Microbial metabolism of polycyclic aromatic hydrocarbons.

A fragment of plasmid NAH7 from Pseudomonas putida PpG7 has been cloned and expressed in Escherichia coli HB101. Growth of the recombinant Escherichia coli in nutrient medium results in the formation of indigo. The production of this dye is increased in the presence of tryptophan or indole. Several bacteria that oxidize aromatic hydrocarbons to cis-dihydrodiols also oxidize indole to indigo. The results suggest that indigo formation is due to the combined activities of tryptophanase and naphthalene dioxygenase.

https://science.sciencemag.org/content/sci/222/4620/167.full.pdf

Expression of naphthalene oxidation genes in Escherichia coli results in the biosynthesis of indigo

The microbial degradation of polychlorinated biphenyls (PCBs) has been extensively studied in recent years The genetic organization of biphenyl catabolic genes has been elucidated in various groups of microorganisms, their structures have been analyzed with respect to their evolutionary relationships, and new information on mobile elements has become available Key enzymes, specifically biphenyl 2,3-dioxygenases, have been intensively characterized, structure/sequence relationships have been determined and enzymes optimized for PCB transformation However, due to the complex metabolic network responsible for PCB degradation, optimizing degradation by single bacterial species is necessarily limited As PCBs are usually not mineralized by biphenyl-degrading organisms, and cometabolism can result in the formation of toxic metabolites, the degradation of chlorobenzoates has received special attention A broad set of bacterial strategies to degrade chlorobenzoates has recently been elucidated, including new pathways for the degradation of chlorocatechols as central intermediates of various chloroaromatic catabolic pathways To optimize PCB degradation in the environment beyond these metabolic limitations, enhancing degradation in the rhizosphere has been suggested, in addition to the application of surfactants to overcome bioavailability barriers However, further research is necessary to understand the complex interactions between soil/sediment, pollutant, surfactant and microorganisms in different environments

Aerobic degradation of polychlorinated biphenyls

Cells of Pseudomonas putida, after growth with naphthalene as sole source of carbon and energy, contain an enzyme that oxidizes (+)-cis-1(r),2(s)-dihydroxy-1,2-dihydronaphthalene to 1,2-dihydroxynaphthalene. The purified enzyme has a molecular weight of 102,000 and apparently consists of four 25,500 molecular weight subunits. The enzyme is specific for nicotinamide adenine dinucleotide as an electron acceptor and also oxidizes several other cis-dihydrodiols. However, no enzymatic activity was observed with trans-1,2-dihydronaphthalene, or the K-region cis-dihydrodiols of carcinogenic polycyclic hydrocarbons.

Purification and Propeties of (+)-cis-Naphthalene Dihydrodiol Dehydrogenase of Pseudomonas putida

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Purification and Propeties of (+)-cis-Naphthalene Dihydrodiol Dehydrogenase of Pseudomonas putida