Methanogenic microbial consortia, originally enriched from anaerobic sewage sludge with ferulic acid or styrene (vinylbenzene) as sole organic carbon and energy sources, were used to study transformation of styrene under strictly anaerobic conditions. Styrene, which was added as the substrate in a range of concentrations from 0.1 to 10 mmol/l, was extensively degraded but no methane production was observed during incubation for eight months. The addition of yeast extract during the enrichment stage completely inhibited degradation of styrene. Gas chromatog‐raphy (GC), gas chromatography/mass spectrometry (GC/MS), high performance liquid chromatography (HPLC) analyses of the culture fluid, and GC analyses of the anaerobic headspace, indicated that the transformation of this arylalkene was initiated through an oxidation‐reduction reaction and that the favoured mechanism was most likely the addition of water across the double bond in the alkenyl side‐chain. The degradation proceeded through to carbon dioxide, the final product. Benzoic acid and phenol were transient compounds found in highest concentrations in the spent culture fluid and are suggested as the key intermediates of the transformation process. The tentative routes of anaerobic transformation partially overlap with those previously proposed for aromatic hydrocarbons such as toluene. Several pure cultures, which were tentatively identified asClostridiumspp. andEnterobacterspp., were isolated from the styrene‐degrading consortia. Two of these cultures were demonstrated to grow on styrene as sole carbon and energy source. Additionally, a pure culture ofEnterobacter cloacaeDG‐6 (ATCC 35929) which had been isolated previously from the ferulate‐degrading consortium, was shown to degrade styrene through to car
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