Literature overview: Microbial metabolism of high molecular weight polycyclic aromatic hydrocarbons

Abstract

High molecular weight polycyclic aromatic hydrocarbons (HMW PAHs) increase in hydrophobicity with increases in their molecular weight and ring angularity. Microbial strategies to deal with PAH hydrophobicity include biofilm formation, enzyme induction, and biosurfactants, the effect of which is variable on PAH metabolism depending on the surfactant type and concentration, substrate, and microbial strain(s). Aerobic HMW PAH metabolism proceeds via mineralization, partial degradation, and cometabolic transformations. Generally, bacteria and nonlignolytic fungi metabolize PAHs via initial PAH ring oxidation by dioxygenases to form cis-dihydrodiols, which are transformed to catechol compounds by dehydrogenases and other mono-and dioxygenases to substituted catechol and noncatechol compounds, all ortho-or metacleaved and further oxidized to simpler compounds. However, lignolytic fungi form quinones and acids to CO 2 . This review discusses the pathways for HMW PAH microbial metabolism. O

Identification of pyrene‐degradation pathways: Bench‐scale studies using Pseudomonas fluorescens 29L

“…A review of these enzymes is given in Husain (2008). Specifically, monooxygenases are substrate-aspecific and incorporate one oxygen atom into the PAH substrate and the other oxygen atom into water with the concomitant oxidation of nicotinamide adenine dinucleotide phosphate (NADPH) (Li et al, 2002).…”

“…On day 6, gentisic acid and pyruvic acid constituted 2.72 percent and 2.16 percent of the carbon mass from pyrene, respectively (Exhibit 8). It is possible that monooxygenases metabolize gentisic acid and pyruvic acid might be formed from the metabolism of other intermediates such as from catechol (Husain, 2008).…”

“…The occurrence of all the above-mentioned pathways in pyrene metabolism in Strain 29L is unique. Other HMW PAH degraders commonly use the ortho, upper or lower, and the Kiyohara pathways (Husain, 2008). The occurrence of both the ortho and the meta pathways in an HMW PAH degrader is not common.…”

“…The United States Environmental Protection Agency 2005 Toxic Release Inventory Public Data estimated that more than 2 million pounds of PAHs were released in the United States in 2005. A review of the physical and chemical properties of HMW PAHs and their microbial metabolism is presented in Husain (2008). Of the 16 PAHs on the US EPA priority pollutants list, 10 are HMW PAHs.…”

“…The most promising and common technology for the treatment of HMW PAH contamination is bioremediation. While studies have shown that HMW PAHs can be degraded (Husain, 2008), there is a need to understand how the biodegradation process occurs at the biochemical level, and one practical approach to meet this need is to conduct bench studies with pyrene, the simplest HMW PAH.…”