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.

Anaerobic phenanthrene mineralization by a carboxylating sulfate-reducing bacterial enrichment

“…Another naphthalene-degrading sulfate-reducing enrichment obtained from an oilcontaminated aquifer initially showed the same pattern Meckenstock et al, 2000). However, a more recent study with the same culture and deuterated naphthalene demonstrated that the initial attack on the parent substrate was methylation to 2-methylnaphthalene, which was subsequently oxidized to 2-naphthoic acid via a fumarate addition reaction (Safinowski and Meckenstock, 2006). The report of naphthalene methylation resembles the recently described methylation of benzene (Ulrich et al, 2005).…”

“…However, if we suppose that the carboxylic acid group containing 13 C that we detected was formed after methylation and subsequent oxidation via fumarate addition, in a manner analogous to naphthalene metabolism (Safinowski and Meckenstock, 2006), we would then have to postulate that an isotopically heavy 13 CH 3 group be formed from the labeled bicarbonate. This prospect is at least theoretically possible.…”

“…However, a more recent study revealed that, at least for one naphthalene-degrading sulfate-reducing enrichment, 2-naphthoic acid was not a direct product of naphthalene activation. Rather, naphthalene was initially methylated to 2-methylnaphthalene before degradation via a fumarate addition and eventually converted into 2-naphthoic acid (Safinowski and Meckenstock, 2006).…”

Intrinsic biodegradation potential of aromatic hydrocarbons in an alluvial aquifer – Potentials and limits of signature metabolite analysis and two stable isotope-based techniques

“…with M S(0) being the amount of 13 C [mmol] added to the bottle at t ¼ 0 d, the first-order rate constant l, and the reciprocal value of the retardation factor 1/F R designating the fraction of contaminant present in the water phase of the microcosms (Schwarzenbach et al, 2003). For hydrophobic compounds such as BTEX and PAH, the correction by F R is necessary to account for sorption to the sediment matrix since only the dissolved compound fraction is readily available for biodegradation.…”

“…Organic carbon-normalized distribution coefficients K OC were predicted from compound class-specific log K OC À log K OW relationships (Schwarzenbach et al, 2003) taking octanolewater coefficients K OW from the Physical Properties Database (SRC Inc., 2009). Half-life times t 1/2 and half-concentration distances x 1/2 were defined as follows:…”