Detection of phenol and benzoate as intermediates of anaerobic benzene biodegradation under different terminal electron-accepting conditions

A sulfate-reducing bacterial enrichment that anaerobically metabolized benz ene was obtained from a petroleum-contaminated aquifer. During biodegradati on, we observed the transient accumulation of phenol and benzoate as putati ve benzene intermediates. As these compounds ape intermediates in many anae robic metabolic pathways, we investigated their relation to anaerobic benze ne decay with C-13-labeled starting material. We were able to confirm the p resence of [C-13]phenol and [C-13]benzoate as intermediates of anaerobic [C -13-UL]benzene decay. Mass spectral evidence indicated that the carboxyl gr oup of benzoate also originated from C-13-labeled benzene. Benzoate was als o found as a putative benzene intermediate when inoculum from the same site was incubated under methanogenic conditions or when organisms enriched fro m a different petroleum-contaminated location were incubated with chelated Fe(III) as an electron acceptor. These findings are the first to confirm th e importance of benzoate during anaerobic benzene metabolism and suggest th at concerns over the accumulation of potentially recalcitrant intermediates in anaerobic environments contaminated with this substrate are unwarranted .