Polycyclic Aromatic Hydrocarbons

The first step in the biotransformation of PAHs (Figure 3) by most fungi is initiated by a cytochrome P450 mono-oxygenase; white-rot basidiomycetes may also employ lignin peroxidase, manganese peroxidase, or laccase (Hammel 1995; Cerniglia 1997; Cerniglia and Sutherland 2001; Sutherland et al. 1995). Later steps may involve conjugation to form sulfates, glucosides, glucuronides, or xylosides (Casillas et al. 1996). Although PAHs do not generally serve as growth substrates for fungi, the yeast R. glutinis is reported to utilize phenanthrene for growth (Romero et al. 1998). The ability of fungi to transform PAHs has been exploited for the bioremediation of contaminated soil (Juhasz and Naidu 2000; Cerniglia and Sutherland 2001).

Naphthalene is oxidized by C. elegans to 1- and 2-naphthol, naphthalene trans-1,2-dihydrodiol, 4-hydroxy-1-tetralone, the 1,2- and 1,4-naphthoquinones, and sulfate and glucuronide conjugates (Cerniglia and Gibson 1977; Cerniglia 1992). Both constitutive and inducible hydroxylases appear to be involved in the pathway (Faber et al. 2001). A. niger has been reported (Yogambal and Karegoudar 1997) to metabolize naphthalene via gentisate, a naphthalene metabolite produced by some bacteria. Naphthalene is removed from wastewater by the immobilized mycelia of P. chrysosporium (Liao et al. 1997).

Acenaphthene is oxidized by C. elegans to 6-hydro-xyacenaphthenone, 1,2-acenaphthenedione, acenaphthene trans-1,2-dihydrodiol, and four minor metabolites (Pothuluri et al. 1992). The laccase of Coriolopsis gallica oxidizes acenaphthene and biphenylene in the presence of an artificial mediator compound, 2,2'-azinobis-(3-ethylbenzthiazoline-6-sulfonate) (ABTS) (Pickard et al. 1999), and the laccase of T. versicolor oxidizes acenaphthene and acenaphthylene in the presence of 4-hydroxybenzoic acid (Johannes and Majcherczyk 2000).

Fluorene is oxidized by C. elegans to 9-hydroxyfluorene, 9-fluorenone, and 2-hydroxy-9-fluorenone (Pothuluri et al. 1993). The first two are also produced by P. chrysosporium, P. ostreatus, and other fungi (Bezalel et al. 1996c; Bogan et al. 1996; Bumpus 1989; Garon et al. 2000; Schutzendubel et al. 1999). The oxidation of fluorene to 9-fluorenone requires manganese peroxidase activity in P. chrysosporium and T. versicolor (Bogan et al. 1996; Collins and Dobson 1996) but not in P. ostreatus or Bjerkandera adusta (Schützendübel et al. 1999). The laccases of C. gallica and T. versicolor are also able to oxidize fluorene (Bressler et al. 2000; Johannes and Majcherczyk 2000).

Anthracene is transformed by C. elegans to a trans-1,2-dihydrodiol and 1-anthryl sulfate (Cerniglia and Yang 1984); 9,10-anthraquinone has also been reported (Lisowska and Dlugonski 1999). Rhizoctonia solani produces the (+) and (—) trans-1,2-dihydrodiols and three xyloside conjugates (Sutherland et al. 1992). Absidia cylindrospora, Rhizopus arrhizus, Ulocladium chartarum, A. niger, Cryphonectria parasitica, and several white-rot fungi also transform anthracene (Field et al. 1996; Giraud et al. 2001; Gramss et al. 1999; Krivobok et al. 1998; Schutzendubel et al. 1999; Yogambal and Karegoudar 1997). P. chrysosporium degrades anthracene via anthraquinone and phthalate to CO2, presumably with the involvement of lignin peroxidase (Hammel et al. 1991). P. ostreatus produces anthraquinone and anthracene trans-1,2-dihydrodiol (Andersson and Henrysson 1996; Bezalel et al. 1996c; Novotny et al. 1999; Schützendübel et al. 1999); in soil, it incorporates the products into humus (Bogan et al. 1999) or degrades them to CO2 (Marquez-Rocha et al. 2000). Pleurotus sajor-caju [P. pulmonarius], T. versicolor, and other fungi also produce anthraquinone (Andersson and Henrysson 1996). Phanero-chaete laevis produces manganese peroxidase and degrades anthracene without accumulating anthraquinone (Bogan and Lamar 1996). The laccases of C. gallica and T. versicolor oxidize anthracene to anthraquinone (Collins et al. 1996; Johannes and Majcherczyk 2000; Pickard et al. 1999); that of Nematoloma frowardii, in the presence of glutathione, can mineralize it (Sack et al. 1997b).

Phenanthrene is oxidized by C. elegans, Syncephalastrum racemosum, and A. niger to trans-dihydrodiols, phenanthrols, and sulfate conjugates (Cerniglia and Yang 1984; Casillas et al. 1996; Sutherland et al. 1993). Glucoside and glucuronide conjugates may also be produced (Casillas et al. 1996). A. niger is reported to produce 1-methoxy-phenanthrene (Sack et al. 1997a) as well as a ring-cleavage product, protocatechuate (Yogambal and Karegoudar 1997). P. chrysosporium degrades phenanthrene (Bumpus 1989), producing trans-9,10- and 3,4-dihydrodiols, 9-, 3-, and 4-phenanthrols, and a glucoside in high-nitrogen media (Sutherland et al. 1991; Sutherland et al. 1993) and phenanthrene-9,10-quinone and 2,2'-diphenic acid in low-nitrogen media (Hammel et al. 1992). P. ostreatus also degrades phenanthrene (Bezalel et al. 1996a; Márquez-Rocha et al. 2000; Schützendübel et al. 1999), producing the trans-9,10-dihydrodiol and 2,2'-diphenic acid (Bezalel et al.

1996b) and phenanthrenequinone (Novotny et al. 1999). Several other fungi, including white-rot and ectomycorrhizal fungi, degrade phenanthrene (Colombo et al. 1996; BraunLullemann et al. 1999; Gramss et al. 1999; Field et al. 1996; Lisowska and Dlugonski 1999; Schtitzendiibel et al. 1999). The manganese peroxidases of P. laevis (Bogan and Lamar 1996), T. versicolor (Collins and Dobson 1996; Rama et al. 2000), and N. frowardii (Sack et al. 1997b) all oxidize phenanthrene. The laccase of Trametes hirsuta, in the presence of the mediator 1-hydroxybenzotriazole and linoleic acid, oxidizes phenanthrene via the quinone to 2,2'-diphenic acid (Bohmer et al. 1998); that of C. gallica, in the presence of ABTS, also oxidizes it (Pickard et al. 1999). Unlike other fungi, the yeast R. glutinis has been reported to utilize phenanthrene as a sole carbon and energy source (Romero et al. 1998).

Fluoranthene is metabolized by C. elegans to a trans-2,3-dihydrodiol, the 8- and 9-hydroxyfluoranthene trans-2,3-dihydrodiols, and two glucoside conjugates (Pothuluri et al. 1990). A. cylindrospora, A. niger, U. chartarum, the yeast Cryptococcus albidus, and the white-rot fungi P. chrysosporium, P. ostreatus, and B. adusta also degrade fluoranthene (Liao et al. 1997; Giraud et al. 2001; Gramss et al. 1999; Salicis et al. 1999; Schutzendubel et al. 1999). P. ostreatus binds fluoranthene metabolites to humus in soil (Bogan et al. 1999).

Pyrene is metabolized to 1-hydroxypyrene, 1,6- and 1,8-pyrenequinones, and three glucoside conjugates by C. elegans (Cerniglia et al. 1986). A. niger produces 1-methoxypyrene and 1-hydroxypyrene (Sack et al. 1997a) and P. glabrum produces these two products plus 1-pyrenyl sulfate, 1,6-dimethoxypyrene, 1,6- and 1,8-dihydroxypyrene, and both quinones (Wunder et al. 1997). Penicillium janthinellum and other fungi found in sediments also degrade pyrene (Launen et al. 2000; Ravelet et al. 2000). P. ostreatus hydroxylates pyrene to the trans-4,5-dihydrodiol and partially mineralizes it (Bezalel et al. 1996a; Bezalel et al. 1996c; Wolter et al. 1997), even in soil (Novotny et al. 1999; Márquez-Rocha et al. 2000). Crinipellis sp., Marasmius sp., and Marasmiellus sp. metabolize it to 1-hydroxy-pyrene, 1,6- and 1,8-dihydroxypyrene, both quinones, pyrene trans-4,5-dihydrodiol, and three sulfate conjugates (Lange et al. 1996). Several other wood-decay and mycorrhizal fungi mineralize pyrene (Braun-Lüllemann et al. 1999; Field et al. 1996; Gramss et al. 1999; in der Wiesche et al. 1996; Schutzendubel et al. 1999; Song 1999), as does the manganese peroxidase of N. frowardii in the presence of glutathione (Sack et al. 1997b).

Benz[a]anthracene, a carcinogen, is hydroxylated by C. elegans to the trans-8,9-,10,11-, and 3,4-dihydrodiols and the 8,9,10,11-tetraol (Cerniglia et al. 1994). P. janthinellum and the white-rot fungi P. chrysosporium, P. ostreatus, P. sajor-caju [P. pulmonarius], and T. versicolor also degrade it (Andersson and Henrysson 1996; Wolter et al. 1997; Boonchan et al. 2000). The manganese peroxidase of P. laevis degrades it during lipid peroxidation; the 7,12-dione is produced but does not accumulate (Bogan and Lamar 1996).

The manganese peroxidase of N. frowardii oxidizes benz[a]anthracene in the presence of glutathione (Sack et al. 1997b).

Chrysene, a weak carcinogen, is metabolized by C. elegans to chrysene 2-sulfate and chrysene 2-hydroxy-8-sulfate (Pothuluri et al. 1995) and by P. janthinellum to the trans-1,2-dihydrodiol (Boonchan et al. 2000; Kiehlmann et al. 1996). S. racemosum, P. ostreatus, and the ectomycorrhizal fungi Boletus edulis and Amanita muscaria also degrade chrysene (Braun-Lüllemann et al. 1999; Kiehlmann et al. 1996; Wolter et al. 1997).

Benzo[b]fluoranthene and benzo[k]fluoranthene, which are both carcinogenic, are degraded in soil extracts by Bjerkandera sp. (Field et al. 1996) and in wheat straw by P. ostreatus (Wolter et al. 1997).

Benzo[a]pyrene, a potent carcinogen, is oxidized by a cytochrome P450 monooxygenase in C. elegans, which transforms it to at least 13 compounds (Figure 4) (Cerniglia and Gibson 1979; Cerniglia 1997). The cytochromes P450 of Aspergillus fumigatus and other fungi also hydroxylate it (Juhasz and Naidu 2000; Venkateswarlu et al. 1996). Several white-rot and ectomycorrhizal fungi degrade benzo[a]pyrene (Bezalel et al. 1996a; Bumpus 1989; Braun-Lüllemann et al. 1999; Kotterman et al. 1998; Marquez-Rocha et al. 2000; Rama et al. 2000; Wolter et al. 1997; Wunch et al. 1999). P. chrysosporium has been used to remove it from water (Liao et al. 1997), and both P. chrysosporium and P. ostreatus form quinones that can be polymerized in soil (Bogan et al. 1999; May et al. 1997). P. laevis produces manganese peroxidase and transforms benzo[a]pyrene to polar products (Bogan and Lamar 1996); the manganese peroxidase of N. frowardii can mineralize it in the presence of glutathione (Sack et al. 1997b). The laccases of T. versicolor, Pycnoporus cinnabarinus, and C. gallica oxidize benzo[a]-pyrene to quinones in the presence of ABTS (Collins et al. 1996; Pickard et al. 1999; Rama et al. 1998).

Benzo[e]pyrene, a noncarcinogenic isomer of benzo-pyrene, is metabolized by C. elegans to sulfate and glucoside conjugates (Pothuluri et al. 1996). Perylene is metabolized by several wood- and straw-degrading fungi (Gramss et al. 1999) and the carcinogenic benzo[ghi ]perylene is degraded by P. ostreatus (Wolter et al. 1997). Dibenz[a,h]anthracene, a suspected carcinogen, is degraded by the white-rot fungi P. ostreatus and P. sajor-caju [P. pulmonarius] (Andersson and Henrysson 1996; Wolter et al. 1997) and by P. janthinellum (Boonchan et al. 2000). Indeno[1,2,3-cd] pyrene, which is also considered carcinogenic, is metabolized by Bjerkandera sp. in solvent extracts of contaminated soil (Field et al. 1996). The methylated PAHs, many of which are carcinogenic, can be oxidized to a variety of metabolites. Methylnaphthalenes, methylanthracenes, methyl- and dimethylbenz[a]anthracenes, and 3-methylcholanthrene are transformed by C. elegans (Cerniglia et al. 1982a; 1982b; 1983; 1984; 1990; Wong et al. 1983). In addition, methylanthracenes are transformed by C. gallica (Pickard et al. 1999) and methylphenanthrenes by Fusarium solani (Colombo et al. 1996).

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