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 benzene was obtained from a petroleum-contaminated aquifer. During biodegradation, we observed the transient accumulation of phenol and benzoate as putative benzene intermediates. As these compounds ape intermediates in many anaerobic metabolic pathways, we investigated their relation to anaerobic benzene decay with C-13-labeled starting material. We were able to confirm the presence of [C-13]phenol and [C-13]benzoate as intermediates of anaerobic [C-13-UL]benzene decay. Mass spectral evidence indicated that the carboxyl group of benzoate also originated from C-13-labeled benzene. Benzoate was also found as a putative benzene intermediate when inoculum from the same site was incubated under methanogenic conditions or when organisms enriched from a different petroleum-contaminated location were incubated with chelated Fe(III) as an electron acceptor. These findings are the first to confirm the importance of benzoate during anaerobic benzene metabolism and suggest that concerns over the accumulation of potentially recalcitrant intermediates in anaerobic environments contaminated with this substrate are unwarranted.