title: Methylation is the initial reaction in anaerobic naphthalene degradation by a sulfate-reducing enrichment culture.
abstract: The sulfate-reducing culture N47 can utilize naphthalene or 2-methylnaphthalene as the sole carbon source and electron donor. Here we show that the initial reaction in the naphthalene degradation pathway is a methylation to 2-methylnaphthalene which then undergoes the subsequent oxidation to the central metabolite 2-naphthoic acid, ring reduction and cleavage. Specific metabolites occurring exclusively during anaerobic degradation of 2-methylnaphthalene were detected during growth on naphthalene, i.e. naphthyl-2-methyl-succinate and naphthyl-2-methylene-succinate. Additionally, all three enzymes involved in anaerobic degradation of 2-methylnaphthalene to 2-naphthoic acid that could be measured in vitro so far, i.e. naphthyl-2-methyl-succinate synthase, succinyl-CoA:naphthyl-2-methyl-succinate CoA-transferase and naphthyl-2-methyl-succinyl-CoA dehydrogenase were also detected in naphthalene-grown cells with similar activities. Induction experiments were performed to study the growth behaviour of the cell when transferred from naphthalene to 2-methylnaphthalene or vice versa. When the cells were transferred from naphthalene to 2-methylnaphthalene they grew immediately, indicating that no new enzymes had to be induced. On the contrary, the transfer of cells from 2-methylnaphthalene to naphthalene caused a lag-phase of almost 100 days demonstrating that an additional catabolic enzyme has to be activated in this case. We propose the methylation as a novel general mechanism of activation reactions in anaerobic degradation of unsubstituted aromatic hydrocarbons.
authors.affiliation: Center for Applied Geosciences, Eberhard-Karls University, Tübingen, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Safinowski
authors.forename: Rainer U
authors.initials: RU
authors.lastname: Meckenstock
mesh_terms: D000693:Anaerobiosis; D001673:Biodegradation, Environmental; D004785:Environmental Pollutants / Q000032:analysis*; D008745:Methylation; D009281:Naphthalenes / Q000032:analysis* / Q000737:chemistry; D016999:Sulfur-Reducing Bacteria / Q000254:growth & development*
chemical_list: D004785:Environmental Pollutants; D009281:Naphthalenes; C031721:naphthalene; C027384:2-methylnaphthalene