Ring fission of anthracene by a eukaryote.

Abstract

Ligninolytic fungi are unique among eukaryotes in their ability to degrade polycyclic aromatic hydrocarbons (PAHs), but the mechanism for this process is unknown. Although certain PAHs are oxidized in vitro by the fungal lignin peroxidases (LiPs) that catalyze lig olysis, it has never been shown that LiPs initiate PAH degradation in vivo. To address these problems, the metabolism of anthracene (AC) and its in vitro oxidation product, 9,10-anthraquinone (AQ), was examined by chromatographic and isotope dilution techniques in Phanerochaete chrysosporium. The fungal oxidation of AC to AQ was rapid, and both AC and AQ were significantly mineralized. Both compounds were cleaved by the fungus to give the same ring-flssion metabolite, phthalic acid, and phthalate production from AQ was shown to occur only under ligninolytic culture conditions. These results show that the major pathway for AC degradation in Phanerochaete proceeds AC -+ AQ --phthalate + CO2 and that it is probably mediated by LiPs and other enzymes of ligninolytic metabolism.Polycyclic aromatic hydrocarbons (PAHs) are major pollutants of both anthropogenic and natural pyrolytic origin, occurring in soils, sediments, and airborne particulates. The crucial step in their biodegradation is oxidative fission of the fused aromatic ring system, an event previously thought unique to certain bacteria (1). Recent evidence necessitates a revision of this view: the lignin-degrading fungi that cause white-rot of wood have also been shown to mineralize a wide variety of aromatic pollutants, including certain PAHs, under culture conditions that promote the expression of ligninolytic metabolism (2-5). A key component of the fungal ligninolytic system is thought to consist of extracellular lignin peroxidases (LiPs), which catalyze the one-electron oxidation of various lignin-related substrates (6-8). LiPs have also been shown to oxidize certain PAHs in vitro, and it has been proposed that they play an important role in the degradation of these pollutants by white-rot fungi (9, 10). However, it has never been demonstrated that LiP-catalyzed oxidation is a significant fate ofany PAH in vivo or that the products of such a reaction are subsequently cleaved to smaller, monocyclic, compounds. In fact, to our knowledge, no PAH ring-fission metabolite other than CO2 has ever been identified in any eukaryote. To address these problems, we have examined the fate of anthracene (AC) in cultures of the ligninolytic basidiomycete Phanerochaete chrysosporium, and we now report that ligninolytic metabolism provides a route for the ring fission of this PAH. AC trans-1,2-dihydrodiol was synthesized from 1,2-dihydroxy-AQ (alizarin) as previously described (12, 13) [ring-'4C]Phthalic acid (12.7 mCi-mmol-1, radiochemical purity >98%) was from Sigma. Unlabeled phthalic acid (99%) and AQ (>98%) were from Kodak. All other reagents were of the highest commercially available quality. MATERIALS AND METHODSTo minimize the artifactual oxidation of AC or its metabolites, all syntheses, cultu...

Conversion of polycyclic aromatic hydrocarbons, methyl naphthalenes and dibenzofuran by two fungal peroxygenases

“…The latter is not surprising since APO does neither possess a dioxygenaselike activity to cleave the ring (Vaillancourt et al 2006) nor an epoxide hydrolase activity that forms dihydrodiols (Yang 1988). One quinone has been detected during Ant oxidation (traces of putative 1,4-anthracenedione) that is in accordance with previous findings on naphthalene ) but differs from reports on LiP and MnP, where 1,9-anthraquinone was the typical quinoid product of Ant oxidation (Hammel et al 1991;Kotterman et al 1994;Eibes et al 2006) or Laccases (Collins et al 1996).…”

Degradation of anthracene, pyrene and benzo[a]-anthracene in aqueous solution by chlorine dioxide

“…Research about the biodegradation of ANTH by Hammel et al [23] revealed that ANTH had almost no biodegradation over a 15-day culture period and degraded slowly such that 30% has been removed after 30 days. While in contrast, 9,10-anthracenedion showed a much better rate of degradation, rapidly degraded by above 80% in only 16 days.…”

Mechanisms for polycyclic aromatic hydrocarbon degradation by ligninolytic fungi.

“…To determine whether such a new pathway exists, we investigated anthracene metabolism in P. chrysosporium (10). 14C-labeled anthracene and anthraquinone (0.2 pM) were supplied to ligninolytic (nitrogen-limited) cultures, and it was shown that '4Co2 evolution from the two compounds was similar (-13% in 14 days).…”