Anthracene is a common polycyclic aromatic hydrocarbon (PAH). Although anthracene itself is not carcinogenic, its biodegradation and metabolism are of interest because the same type of fused ring structures are found in higher molecular weight PAHs such as benz[a]anthracene and benzo[a]pyrene, which are carcinogenic. Anthracene and other PAHs are found in crude oil, coal tar and creosote. They are also formed via pyrosynthesis during incomplete combustion. Following fractional distillation of coal tar, the fraction boiling above 270° C is known as "anthracene oil." In addition to anthracene, anthracene oil also contains phenanthrene, fluorene, fluoranthene, pyrene and carbazole. Bacteria can degrade anthracene, as shown elsewhere. Fungi also can degrade anthracene.
White rot fungi often prepare aromatic compounds for ring cleavage by first converting them to quinones. The initial oxidation of anthracene (to 9,10-anthraquinone), benzo[a]pyrene (Haemmerli, et al., 1986) and several other PAHs is catalyzed by lignin peroxidases from Phanerochaete chrysporium, Bjerkandera sp. strain BOS55 (Field, J.A. et al., Enzyme and Micro. Tech. 18:300-308, 1996) and other white rot fungi. Manganese peroxidases, another family of lignin degrading peroxidases produced by white rot fungi, can also oxidize anthracene (Eibes et al., 1986). Laccases, copper-containing enzymes that are also involved in lignin degradation by Trametes versicolor, have also been shown to oxidize anthracene (Collins et al., 1986). Not all white rot fungi produce laccases. P. chrysosporium can completely mineralize anthracene. It cleaves 9,10-anthraquinone to phthalate and, here proposed, catechol, though o-benzoquinone or aliphatic compounds are also possible (Hammel et al., 1991).
Not all fungi that metabolize anthracene completely mineralize it. Others detoxify anthracene by conjugation followed by secretion. Cunninghamella elegans oxidizes anthracene to anthracene-1,2-oxide using a cytochrome P450 monooxygenase (Cerniglia, 1997). This can be further oxidized to anthracene-trans-1,2-dihydrodiol (Cerniglia and Yang, 1983), or oxidized to 1-anthrol non-enzymatically. 1-Anthrol can form conjugates with xylose, glucuronate and sulfate (Sutherland et al., Myco. Res., 96: 509-517, 1992).
The following is a text-format anthracene (fungal) pathway map. Organisms which can initiate the pathway are given, but other organisms may also carry out later steps. Follow the links for more information on compounds or reactions. This map is also available in graphic (5K) format.
Anthracene Anthracene Anthracene Phanerochaete chrysosporium Bjerkandera sp. BOS55 Trametes versicolor Bjerkandera sp. BOS55 | | Pleurotus ostreatus | | | | | | lignin peroxidase | manganese peroxidase | laccase | | | | | | | | | | v | +------------------> 9,10-Anthraquinone <-------------------+ ^ | from the | | Anthracene -------+ v A Pathway | | v Phthalate + [Catechol] | | | | | | v v to the to the Phthlate Family Nitrobenzene Pathway Pathway
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