Polycyclic aromatic hydrocarbons (PAHs), such as phenanthrene are commonly found as pollutants in soils, estuarine waters and sediments, and other terrestrial and aquatic sites. Phenanthrene has been shown to be toxic to marine diatoms,gastropods, mussels, crustaceans, and fish.
Besides the bacterial metabolic pathways of phenanthrene , fungi can also metabolize phenanthrene. Nonligninolytic (i.e., high-N) cultures of Phanerochaete chrysosporium fit the typical eukaryotic pattern. They metabolize phenanthrene to trans-dihydrodiols and phenanthrene conjugates. Phenanthrene trans-9,10- and trans-3,4-dihydrodiols are formed by the successive activities of monooxygenases and epoxide hydrolases. The regiospecificity of P. chrysosporium differs from that of Cunninghamell elegans, which principally produces the trans-1,2- dihydrodiol with smaller amounts of the trans-3,4-dihydrodiol. There was no metabolism at 9, 10- positions ("K-region") of phenanthrene as evidenced by the failure to detect trans-9,10-dihydrodiols. The three phenanthrols were most likely produced either by dehydration of the trans-dihydrodiols or by rearrangement of the postulated arene oxides (reactions: A, B, J, K, C and D). Similarly, in Cunninghamell elegans, 1-phenanthrol was produced via dehydration of the corresponing trans-1,2-dihydrodiols (reaction I). The novel 9-phenanthryl-beta -D-glucopyranoside produced by P. chrysosporium differs from the 1-phenanthryl-beta- D-glucopyranoside produced by C. elegans. Those conjugates may be considered detoxification products of phenanthrene.
Unlike nonligninolytic Phanerochaete chrysosporium, ligninolytic Phanerochaete chrysosporium does not accumulate trans-dihydrodiols and phenanthrols (Hammel KE, et al., 1992). It gives 2,2'-diphenic acid (DPA) as a major fate of phenanthrene by 9,10-oxidation and ring cleavage (reactions E and F). These two reactions could involve multiple steps. However, no intermediates were reported so far. The oxidation of phenanthrene-9,10-quinone (PQ) to DPA involves both fungal and abiotic mechanisms, and is unaffected by the level of nitrogen added. Phenanthrene degradation by ligninolytic P. chrysosporium involves both ligninolytic and nonligninolytic enzymes and is not initiated by a classical microsomal cytochrome P-450. In reaction H, 2,2'-biphenyldimethanol occurred as a minor phenanthrene metabolite which was probably a reduction product of DPA. Both phenanthrene and PQ could be mineralized to similar extents by this kind of fungus. For reaction G, it is likely that some DPA formed from phenanthrene and PQ was further degraded, but it remains uncertain whether DPA is an obligatory intermediate in phenanthrene.
Metabolism of phenanthrene by Phanerochaete chrysosporium, A.quadruplicatum PR-6, and S. flavovirens all produce phenanthrene trans-9S,10S-dihydrodiol as the predominant metabolite. However, the cytochrome P-450 and epoxide hydrolase of P. ostreatus, C. elegans, and S. racemosum favor the stereoselective formation of phenanthrene trans-9R,10R-dihydrodiol.
The following is a text-format Phenanthrene 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 (32 k) format.
Phenanthrene Phenanthrene Phenanthrene nonligninolytic ligninolytic Cunninghamella elegans chrysosporium | | ATCC 24725 from the | | | Phenanthrene --+ | | | fungal | | | | (9R,10R) | v E | | Pathway | | | +---------+---------+ | | +-------+-------+ | | +---+ | | | | | | v v | | from the | phenanthrene | phenanthrene |9,10-Phenanthrene- | phenanthrene | phenanthrene Phenanthrene | 3,4- | 9,10- | quinone | 3,4- | 1,2- fungal | monooxygenase | monooxygenase| | | monooxygenase | monooxygenase (9R,10R) | | | | | | +-------------- Pathway v v | | v v v +--[Phenanthrene- [Phenanthrene- <-----+ | F [Phenanthrene- [Phenanthrene- to the | 3,4-oxide] 9,10-oxide] | | +-> 3,4-oxide] 1,2-oxide] -----> Phenanthrene | | | | | | | | | (bacterial) | | | | | | | | | Pathway | | | phenanthrene-| phenanthrene-| v | | phenanthrene- | phenanthrene |A |B | 3,4-epoxide | 9,10-epoxide +> 2,2'-Diphenate| | 3,4-epoxide | 1,2-epoxide | | | hydrolase | hydrolase | | | | hydrolase | hydrolase | | v | | | | v | | | trans- | | | | trans- | | | 3,4-Dihydrodiol- v | | | 3,4-Dihydrodiol- v | | phenanthrene trans- | | +> phenanthrene trans- | \ ^ 9,10-Dihydrodiol- | v | 1,2-Dihydrodiol- | \ | +- phenanthrene | | +---------+------> phenanthrene | \ | | | | +---+-------+ | | v v | | | | D | G | from the | 3-phen- 4-phen- | | | | v | Phenanthrene | anthrol anthrol | | | | CO2 | H fungal | I ^ ^ | | | | | (9R,10R) | | J | K | | | C | | Pathway | +--------+-----+ | | | v | v to the | | | | 2,2'-Biphenyl- -+---> [1-Phenanthrol] ---> Phenanthrene | | | | dimethanol | (bacterial) | | | | | Pathway | | | | | | | v | | 1-phenanthrol | | 9-Phenanthrol <-------+-----------+ | glycosyltransferase | | ^ | | | | | | | | | v | | | | | | to the v | | | | +---------------> Phenanthrene 1-Phenanthryl- to the | | | | (bacterial) beta-D-glucopyranoside Phenanthrene <----+ | | 9-phenanthrol Pathway (bacterial) | | | glycosyltransferase Pathway | | | +-----+----+ | | | from the | Phenanthrene v fungal 9-Phenanthryl- (9R,10R) beta-D-glucopyranoside Pathway
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