Anaerobic Naphthalene Degradation by a Sulfate-Reducing Enrichment Culture

Abstract

Anaerobic naphthalene degradation by a sulfate-reducing enrichment culture was studied by substrate utilization tests and identification of metabolites by gas chromatography-mass spectrometry. In substrate utilization tests, the culture was able to oxidize naphthalene, 2-methylnaphthalene, 1-and 2-naphthoic acids, phenylacetic acid, benzoic acid, cyclohexanecarboxylic acid, and cyclohex-1-ene-carboxylic acid with sulfate as the electron acceptor. Neither hydroxylated 1-or 2-naphthoic acid derivatives and 1-or 2-naphthol nor the monoaromatic compounds ortho-phthalic acid, 2-carboxy-1-phenylacetic acid, and salicylic acid were utilized by the culture within 100 days. 2-Naphthoic acid accumulated in all naphthalene-grown cultures. Reduced 2-naphthoic acid derivatives could be identified by comparison of mass spectra and coelution with commercial reference compounds such as 1,2,3,4-tetrahydro-2-naphthoic acid and chemically synthesized decahydro-2-naphthoic acid. 5,6,7,8-Tetrahydro-2-naphthoic acid and octahydro-2-naphthoic acid were tentatively identified by their mass spectra. The metabolites identified suggest a stepwise reduction of the aromatic ring system before ring cleavage. In degradation experiments with [1-13 C]naphthalene or deuterated D 8 -naphthalene, all metabolites mentioned derived from the introduced labeled naphthalene. When a [13 C]bicarbonate-buffered growth medium was used in conjunction with unlabeled naphthalene, 13 C incorporation into the carboxylic group of 2-naphthoic acid was shown, indicating that activation of naphthalene by carboxylation was the initial degradation step. No ring fission products were identified.Polycyclic aromatic hydrocarbons (PAH) are hazardous compounds which are found on various contaminated sites such as former gas plant sites or mineral oil refineries. Due to their obvious persistence in anoxic environments, PAH have been considered to be recalcitrant under anoxic conditions. However, anaerobic degradation of naphthalene, methylnaphthalene, phenanthrene, and a few more PAH has been demonstrated in microcosm experiments converting trace amounts of radioactively labeled substrates to CO 2 (8,9,20,23,26). Nitrate, sulfate, or ferric iron served as the terminal electron acceptor. Whereas anaerobic degradation of toluene and ethylbenzene has been investigated with several pure cultures (1,4,10,11,15,21,22,24), attempts to cultivate anaerobic PAHdegrading bacteria have failed for a long time (18). A sulfatereducing enrichment culture of marine origin growing with naphthalene as the sole carbon and energy source has been reported recently (31). 2-Naphthoic acid and phenanthroic acid were identified as metabolites of naphthalene and phenanthrene degradation, respectively. [ 13 C]bicarbonate was incorporated into the carboxylic group of 2-naphthoic acid, and it was assumed that a carboxylation reaction was the initial step. Since the culture could also use this compound as a carbon source, it was suggested to be the first intermediate in anaerobic naphthalene degradation...

Anaerobic phenanthrene mineralization by a carboxylating sulfate-reducing bacterial enrichment

“…In that study, a marine enrichment culture was found to initially attack both phenanthrene and naphthalene by direct carboxylation from an inorganic source, confirmed by the incorporation of 13 Clabeled bicarbonate in both parent molecules (Zhang and Young, 1997). 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).…”

Biodegradation of Phenolic and Polycyclic Aromatic Compounds by Some Algae and Cyanobacteria

“…Erickson and Fan [28] have summarized information on anaerobic biodegradation of a number of aromatic compounds by means of photometabolism, anaerobic respiration using nitrate or sulfate, and methanogenic fermentation [29,30], however, they proposed hydroxylation as the initial step in naphthalene biotransformation under sulfate-reducing conditions. Bauer JE and Capone DG [31] performed a laboratory study on the degradation of anthracene and naphthalene by the microbiota.…”

Recent Advances in Petroleum Microbiology

“…Work with microbial consortia in the field, in enrichment cultures, and in microcosms has illustrated that hydrocarbons such as toluene (171,358), alkylbenzenes including m-, o-, and p-xylene and trimethylbenzenes (39,111,235,481), benzene (90,312,521), naphthalene and phenanthrene (50,124,421,686), methylnaphthalene and tetralin (20,23), ϾC 6 n-alkanes (18,96,168,575), branched alkanes (72,73), and hydrocarbon mixtures (228) can be metabolized under anaerobic conditions. These reactions may take place under Fe(III)-reducing, denitrifying, and sulfate-reducing conditions, by anoxygenic photosynthetic bacteria, or in syntrophic consortia of proton-reducing and methanogenic bacteria.…”