The anaerobic biodegradation ofo-, m- andp-cresol by sulfate-reducing bacterial enrichment cultures obtained from a shallow anoxic aquifer

Abstract

Sulfate-reducing bacterial enrichments were obtained from a shallow anoxic aquifer for their ability to metabolize either or, mr, or p-cresol. GC/MS and simultaneous adaptation experiments suggested that the anaerobic decomposition of p-cresol proceeds by the initial oxidation of the aryl methyl group to form p-hydroxybenzoic acid. This intermediate was then converted to benzoic acid. Benzoic acid and a hydroxybenzaldehyde were also found in spent culture fluids from an o-cresol-degrading enrichment culture. This result, in addition to others, suggested that o-cresol may also be anaerobically degraded by the oxidation of the methyl substituent. An alternate pathway for anaerobic m-cresol decomposition might exist. Enrichment cultures obtained with either p-or o-cresol degraded both of these substrates but not m-cresol, In contrast, a m-cresol enrichment culture did not metabolize the ortho or para isomers. Anaerobic biodegradation in all enrichment cultures was inhibited by molybdate and oxygen, and was dependent on the presence of sulfate as a terminal electron acceptor. The stoichiometry of sulfate-reduction and substrate depletion by the various enrichment cultures indicated that the parent cresol isomers were completely mineralized. This result was confirmed by the conversion of 14C-labeled p-cresol to 14CO2. These results help clarify the fate of alkylated aromatic chemicals in anoxic aquifers.