Anaerobic production and transformation of aromatic hydrocarbons and substituted phenols by ferulic acid-degrading BESA-inhibited methanogenic consortia

Sewage sludge-derived methanogenic enrichments degrading ferulic acid as sole carbon and energy source were partially inhibited with 2-bromoethanesulfonic acid. The various intermediates and products formed under inhibition of methanogenesis were studied using gas chromatography/mass spectrometry (GC/MS). In addition to aromatic, alicyclic, and aliphatic acids previously shown to be intermediates of ferulate degradation to CO2 and CH4, the following compounds were detected: toluene, ethylbenzene, phenol, p-cresol, 2-ethylphenol, catechol, and 3-hydroxy-4-ethylphenol. The character and the sequence of appearance of the compounds indicate that fermentative bacteria which initiate the anaerobic transformation of ferulic acid, in case of disruption of interspecies hydrogen transfer, dispose of electrons by converting part of the substrate to reduced derivatives. Aromatic hydrocarbons are further partially oxidized through hydroxylation of the ring (and, to a lesser extent, the side-chain), and partially reduced to saturated alicyclic rings. Some of these compounds seem to be gradually degraded to branched or straight- chain aliphatic acids. Some compounds, like catechol and ethylphenol, accumulate transiently or persistently in high concentrations (up to 16 mM carbon out of the initial concentration of 30 mM substrate carbon), indicating that hydroxylation of the aromatic ring might be an important metabolic reaction in these systems.