Carboxylation as an initial reaction in the anaerobic metabolism of naphthalene and phenanthrene by sulfidogenic consortia

The anaerobic biodegradation of naphthalene (NAP) and phenanthrene (PHE) was investigated by using sediment collected from the Arthur Kill in New York/New Jersey harbor. The initial cultures were composed of 10% sediment and 90% mineral medium containing 20 mM sulfate. Complete loss of NAP and PHE (150 to 200 μM) was observed after 150 days of incubation. Upon refeeding, NAP and PIlE were utilized within 14 days. The utilization of both compounds was inhibited in the presence of 20 mM molybdate. [¹⁴C]NAP and [¹⁴C]PHE were mineralized to ¹⁴CO₂. The activities could be maintained and propagated by subculturing in mineral medium. In the presence of halogenated analogs, 2-naphthoate was detected in NAP-utilizing enrichments. The mass spectrum of the derivatized 2-naphthoate from the enrichment supplemented with both [¹³C]bicarbonate and NAP indicates the incorporation of ¹³CO₂ into NAP. In the PHE-utilizing enrichment, a metabolite was detected by both high-pressure liquid chromatography and gas chromatography-mass spectrometry analyses. The molecular ion and fragmentation pattern of its mass spectrum indicate that it was phenanthrenecarboxylic acid. The results obtained with [¹³C]bicarbonate indicate that ¹³CO₂ was incorporated into PHE. It appears, therefore, that carboxylation is an initial key reaction for the anaerobic metabolism of NAP and PHE. To our knowledge, this is the first report providing evidence for intermediates of PAH degradation under anaerobic conditions.