2-methylnaphthalene is one of the most toxic constituents of the water-soluble fraction of crude and fuel oils (Basu et al., 2003; Murata et al., 1997). Given its potential to contaminate groundwater and other resources, the capacity of microorganisms to degrade it in situ is of considerable interest.
2-Methylnaphthalene is readily metabolized under aerobic conditions (Mahajan et al., 1994), and the well documented aerobic 2-methylnaphthalene degradation pathway is described elsewhere in this database. More recently, an anaerobic degradation pathway has been demonstrated in the laboratory and several of its metabolites found in subsurface petroleum reservoirs, providing evidence for its widespread occurence in nature (Aitken et al., 2004).
Although efforts to isolate a particular strain capable of carrying out this pathway have not yet been successful, multiple studies have documented the degradation of 2-methylnaphthalene to 2-naphthoic acid by sulfate-reducing bacterial cultures (e.g., Annweiler et al., 2000; Zang et al., 2000). The pathway listed here, proposed by Safinowski and Meckenstock (2004), begins with the addition of fumerate to the 2-methyl group, followed by conversion to 2-naphthoic acid. The aromatic rings are then reduced and broken (Annweiler et al., 2002). Some metabolites in these latter steps of the pathway are very likely CoA esters but are depicted as free acids because the CoA esters have not yet been identified.
The following is a text-format 2-methylnaphthalene anaerobic pathway map. An isolated culture which can initiate the pathway is 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 (14k) format.
2-Methylnaphthalene sulfate-reducing enrichment culture N47 | | | benzylsuccinate | synthase | v Naphthyl-2-methyl-succinate | | | naphthyl-2-methyl- | succinate CoA- | transferase | v Naphthyl-2-methyl-succinyl-CoA | | | naphthyl-2- | methyl-succinyl-CoA | dehydrogenase | v Naphthyl-2-methylene-succinyl-CoA | | | naphthyl-2- | methylene-succinyl- | CoA lyase | v Naphthyl-2-hydroxymethyl-succinyl-CoA | | | naphthyl-2-hydroxymethyl- | succinyl-CoA | dehydrogenase | v Naphthyl-2-oxomethyl-succinyl-CoA | | | naphthyl-2-oxomethyl- | succinyl-CoA succinyl | transferase | v 2-Naphthoyl-CoA | | | 2-naphthoate | CoA-transferase | v 2-Naphthoate | | | A v | v 5,6,7,8-Tetrahydro-2-naphthoate | | | B v | v 2-Carboxycyclohexylacetate | | | C v | v Carbon dioxide
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