Detection of Phenol and Benzoate as Intermediates of Anaerobic Benzene Biodegradation under Different Terminal Electron-Accepting Conditions

Abstract

A sulfate-reducing bacterial enrichment that anaerobically metabolized benzene was obtained from a petroleumcontaminated aquifer. During biodegradation, we observed the transient accumulation of phenol and benzoate as putative benzene intermediates. As these compounds are intermediates in many anaerobic metabolic pathways, we investigated their relation to anaerobic benzene decay with 13 C-labeled starting material. We were able to confirm the presence of [ 13 C]phenol and [ 13 C]benzoate as intermediates of anaerobic [ 13 C-UL]benzene decay. Mass spectral evidence indicated that the carboxyl group of benzoate also originated from 13 C-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.

Hydroxylation and Carboxylation—Two Crucial Steps of Anaerobic Benzene Degradation by Dechloromonas Strain RCB

“…The environmental implications of such extracellular processing of benzene to more readily degradable substrates and the availability of these substrates to other organisms in the natural environment are currently unknown. Although the concentrations of phenol and benzoate detected in our studies are very low, they are in agreement with previous reports on intermediates formed during anaerobic benzene and toluene degradation (4,10). Prior studies detected phenol, cyclohexanone, and propionate as potential intermediates in undefined methanogenic enrichments incubated with benzene (21,37).…”

“…Prior studies detected phenol, cyclohexanone, and propionate as potential intermediates in undefined methanogenic enrichments incubated with benzene (21,37). Similarly, phenol, benzoate, and acetate were also detected in benzene-degrading iron-reducing and sulfate-reducing sediments (10). As Dechloromonas species are not known to grow by Fe(III) reduction, by sulfate reduction, or through syntrophic interactions with methanogenic bacteria (13,17), it is unlikely that organisms closely related to strain RCB or JJ are involved in the benzene metabolism observed in the previous studies.…”

“…Previous studies of methanogenic benzene-degrading enrichments have indicated that phenol, cyclohexanone, propionate, and acetate are possible metabolites (21,36,37). Furthermore, phenol and benzoate were both detected as intermediates of benzene degradation with sulfate-reducing and Fe(III)-reducing enrichments (10,32). However, all of these studies were performed with undefined sediments or enrichment cultures, and whether the compounds were formed directly from benzene catabolism by a single organism or were formed as a result of several sequential metabolic steps involving several different organisms is unknown.…”

Anaerobic Catabolism of Aromatic Compounds: a Genetic and Genomic View

“…Phenol and benzoate, which have been detected in the culture medium of methanogenic, sulfate-reducing, and iron-reducing mixed cultures, are thought to be potential metabolites of anaerobic benzene biodegradation. A direct methylation of benzene to toluene has also been proposed (49,65,365). Interestingly, the anaerobic nitrate-dependent benzene degradation by Dechloromonas aromatica strain RCB appears to involve an initial hydroxylation with the formation of phenol.…”

Simultaneous Elimination of Carbon and Nitrogen Compounds of Petrochemical Effluents by Nitrification and Denitrification

“…However, most studies with consortia have shown that benzene seems to be recalcitrant to biodegradation under denitrifying conditions in both cases: in mixtures and as a sole electron donor. In this sense, it has been suggested that benzene is not consumed due to the lack of oxidizing enzymes (Gülensoy & Alvarez, 1999) and/or to the high structural stability of benzene (Cadwell & Sufita, 2000). Likewise, toxic effects on bacteria cell membranes have been proposed (Sikkema et al, 1994).…”