Anaerobic cometabolic conversion of benzothiophene by a sulfate-reducing enrichment culture and in a tar-oil- contaminated aquifer

Anaerobic cometabolic conversion of benzothiophene was studied with a sulfa te-reducing enrichment culture growing with naphthalene as the sole source of carbon and energy. The sulfate-reducing bacteria were not able to grow w ith benzothiophene as the primary substrate. Metabolite analysis was perfor med with culture supernatants obtained by cometabolization experiments and revealed the formation of three isomeric carboxybenzothiophenes. Two isomer s were identified as 2-carboxybenzothiophene and 5-carboxybenzothiophene. I n some experiments, further reduced dihydrocarboxybenzothiophene was identi fied. No other products of benzothiophene degradation could be determined. In isotope-labeling experiments with a [C-13]bicarbonate-buffered culture m edium, carboxybenzothiophenes which were significantly enriched in the C-13 content of the carboxyl group were formed, indicating the addition of a C- 1 unit from bicarbonate to benzothiophene as the initial activation reactio n. This finding was consistent with the results of earlier studies on anaer obic naphthalene degradation with the same culture, and we therefore propos e that benzothiophene was cometabolically converted by the same enzyme syst em. Groundwater analyses of the tar-oil-contaminated aquifer from which the naphthalene-degrading enrichment culture was isolated exhibited the same c arboxybenzothiophene isomers as the culture supernatants. In addition, the benzothiophene degradation products, in particular, dihydrocarboxybenzothio phene, were significantly enriched in the contaminated groundwater to conce ntrations almost the same as those of the parent compound, benzothiophene. The identification of identical metabolites of benzothiophene conversion in the sulfate-reducing enrichment culture and in the contaminated aquifer in dicated that the same enzymatic reactions were responsible for the conversi on of benzothiophene in situ.