Anaerobic degradation of alkylated benzenes in denitrifying laboratory aquifer columns

Abstract

Toluene and m-xylene were rapidly mineralized in an anaerobic laboratory aquifer column operated under continuous-flow conditions with nitrate as an electron acceptor. The oxidation of toluene and m-xylene was coupled with the reduction of nitrate, and mineralization was confirmed by trapping 14CO2 evolved from 14C-ring-labeled substrates. Substrate degradation also took place when nitrous oxide replaced nitrate as an electron acceptor, but decomposition was inhibited in the presence of molecular oxygen or after the substitution of nitrate by nitrite. The m-xylene-adapted microorganisms in the aquifer column degraded toluene, benzaldehyde, benzoate, m-toluylaldehyde, m-toluate, m-cresol, p-cresol, and p-hydroxybenzoate but were unable to metabolize benzene, naphthalene, methylcyclohexane, and 1,3-dimethylcyclohexane. Isotope-dilution experiments suggested benzoate as an intermediate formed during anaerobic toluene metabolism. The finding that the highly water-soluble nitrous oxide served as electron acceptor for the anaerobic mineralization of some aromatic hydrocarbons may offer attractive options for the in situ restoration of polluted aquifers.

Functional analysis of an anaerobic m-xylene-degrading enrichment culture using protein-based stable isotope probing

“…Much less is known regarding the anaerobic degradation of xylene isomers. Degradation of xylene isomers under anoxic conditions was described for enrichment cultures under nitrate-reducing (Kuhn et al, 1988;Evans et al, 1991;Haner et al, 1995;Rotaru et al, 2010), iron-reducing (Jahn et al, 2005;Botton & Parsons, 2006), and sulfatereducing (Edwards et al, 1992;Morasch & Meckenstock, 2005;Nakagawa et al, 2008;Herrmann et al, 2009) conditions. A few isolates were reported to grow with m-xylene (Dolfing et al, 1990;Fries et al, 1994;Rabus & Widdel, 1995;Harms et al, 1999;Morasch et al, 2004) or o-xylene (Harms et al, 1999;Morasch et al, 2004); no pure culture was described yet degrading p-xylene anaerobically.…”

Anaerobic utilization of alkylbenzenes and n‐alkanes from crude oil in an enrichment culture of denitrifying bacteria affiliating with the β‐subclass of Proteobacteria

“…Therefore, anaerobic degradation of oil hydrocarbons has been most intensively studied with BTEX, in particular with toluene. Anaerobic degradation of toluene has been investigated in microbial communities (Grbić-Galić and Vogel, 1987;Kuhn et al, 1988;Edwards and Grbić-Galić, 1992) and pure cultures of denitrifying (Dolfing et al, 1990;Altenschmidt and Fuchs, 1991;Evans et al, 1991;Schocher et al, 1991;Fries et al, 1994;Rabus and Widdel, 1995a;Hess et al, 1997), ferric iron-reducing (Lovley and Lonergan, 1990) and sulphate-reducing (Rabus et al, 1993;Beller et al, 1996) bacteria. The mechanism of anaerobic toluene activation has been elucidated recently (Biegert et al, 1996;Beller and Spormann, 1997;Leuthner et al, 1998;Rabus and Heider, 1998).…”

Literature overview: Microbial metabolism of high molecular weight polycyclic aromatic hydrocarbons

“…However, it is known that under anaerobic conditions, substituted aromatic compounds appear to be more readily degraded than nonsubstituted ones since the addition of a substituent's electron-donating group on the benzene ring allows initial oxidation via the splitting of water to provide oxygen (Hutchins, 1991;Wilson & Bouwer, 1997). For example, the anaerobic degradation of toluene initially involves the oxidation of the methyl substituents to produce 4-hydroxybenzoic acid, which then undergo further oxidation using water (Kuhn et al, 1988).…”