Anaerobic naphthalene degradation by a sulfate-reducing enrichment culture

Anaerobic naphthalene degradation by a sulfate-reducing enrichment culture was studied by substrate utilization tests and identification of metabolite s 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 aci d, and cyclohex-1-ene-carboxylic acid with sulfate as the electron acceptor . Neither hydroylated 1- or 2-naphthoic acid derivatives and 1- or 2-naphth ol nor the monoaromatic compounds ortho-phthalic acid, 2-carboxy-1-phenylac etic 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 spectr a and coelution with commercial reference compounds such as 1,2,3,4-tetrahy dro-2-naphthoic acid and chemically synthesized decahydro-2-naphthoic acid. 5,6,7,8-Tetrahydro-2-naphthoic acid and octahydro-2-naphthoic acid were te ntatively identified by their mass spectra, The metabolites identified sugg est a stepwise reduction of the aromatic ring system before ring cleavage. In degradation experiments with [1-C-13]naphthalene or deuterated D-8-napht halene, all metabolites mentioned derived from the introduced labeled napht halene. When a [C-13] bicarbonate-buffered growth medium was used in conjun ction with unlabeled naphthalene, 13C incorporation into the carboxylic gro up of 2-naphthoic acid was shown, indicating that activation of naphthalene by carboxylation was the initial degradation step. No ring fission product s were identified.