Influence of Alternate Electron Acceptors on the Metabolic Fate of Hydroxybenzoate Isomers in Anoxic Aquifer Slurries

Abstract

The biodegradation of hydroxybenzoate isomers was investigated with samples obtained from two sites within a shallow anoxic aquifer. The metabolic fates of the substrates were compared in denitrifying, sulfate-reducing, and methanogenic incubations. Under the latter two conditions, phenol was detected as a major intermediate of p-hydroxybenzoate, but no metabolites were initially found with m-or o-hydroxybenzoate. However, benzoate accumulation was noted when metabolic inhibitors were used with these samples. About 9 to 17 days was required for >95% removal of the parent isomers under these conditions. When aquifer slurries were amended with nitrate, the equivalent removal of the hydroxybenzoates occurred within 4 days. In the denitrifying incubations, phenol was formed from all three hydroxybenzoates and accounted for about 30% of the initial substrate amendment. No benzoate was measured in these samples. All metabolites were identified by chromatographic mobility, mass spectral profiles, or both. Autoclaved controls were uniformly incapable of transforming the parent substrates. These results suggest that the anaerobic fate of hydroxybenzoate isomers depends on the relative substitution pattern and the prevailing ecological conditions. Furthermore, since these compounds are central metabolites formed during the breakdown of many aromatic chemicals, our findings may help provide guidelines for the reliable extrapolation of metabolic fate information from diverse anaerobic environments.

The extent of fermentative transformation of phenolic compounds in the bioanode controls exoelectrogenic activity in a microbial electrolysis cell

“…Therefore, benzoic acid is not considered an important metabolite of HBA under the experimental conditions of the present study. The biotransformation of HBA to phenol has been reported in an enriched fermentative/methanogenic culture (Tschech and Schink, 1986), anoxic aquifer samples (Kuhn et al, 1989), and a pure culture of Clostridium strain JW/Z-1 (Zhang and Wiegel, 1990). (Fig.…”

“…In a review by Schink et al (2000), catechol was regarded as the most slowly degraded divalent phenol under anoxic conditions. Tschech and Schink (1986) reported that phenol, produced from HBA, was slowly degraded in several weeks, whereas Kuhn et al (1989) observed a fast degradation of phenol in 4 days. An earlier study reported that all SA, VA, HBA, catechol and phenol were degraded within 34 days, with more than 60% of the carbon converted to CH 4 and CO 2 (Healy and Young, 1979).…”

Purification and Characterization of an Oxygen-Sensitive Reversible 4-Hydroxybenzoate Decarboxylase from Clostridium hydroxybenzoicum

“…Degradation of aromatic compounds in the absence of molecular oxygen has also been documented and is hypothesized to involve reduction of the aromatic ring(s) as a general mechanism (Berry et al, 1987;Fuchs et al, 1994). Decarboxylation and carboxylation of aromatic compounds have been proposed to play important initial roles in the anaerobic degradation of aromatic compounds, especially hydroxybenzoates and phenols (Gallert and Winter, 1992;Hsu et al, 1990;Kuhn et al, 1989;Zhang and Wiegel, 1990a). Zhang and Wiegel (1990b) presented a sequential pathway for the degradation of 2,4-dichlorophenol in both methanogenic sediments and enrichment cultures in which the dechlorinated product, phenol, is converted to benzoate before ring cleavage.…”

Cloning, Characterization, and Expression of a Novel Gene Encoding a Reversible 4-Hydroxybenzoate Decarboxylase from Clostridium hydroxybenzoicum

“…Decarboxylation and carboxylation of aromatic compounds have been proposed to play important initial roles in the anaerobic degradation of (hydroxy)arylic acids (e.g., hydroxybenzoic acids) and phenolic compounds in methanogenic environments (2,12,19,24,(33)(34)(35). Zhang and Wiegel (33) proposed a pathway comprised of the sequential actions of at least six bacteria for the mineralization of 2,4-dichlorophenol.…”