Anaerobic formation of the aromatic hydrocarbon p-cymene from monoterpenesby methanogenic enrichment cultures

The fate of monoterpenes in methanogenic habitats was investigated in enric hment cultures using defined mineral media inoculated with activated sludge and R-(-)-alpha-phellandrene, (+)-2-carene, (-)-alpha-pinene, or (+)-sabin ene. The anaerobic biodegradation of alpha-pinene and 2-carene supported me thanogenesis. In contrast, consumption of alpha-phellandrene and sabinene w as accompanied by formation of the aromatic hydrocarbon p-cymene. This arom atization reaction did not occur in pasteurized or autoclaved cultures or i n the absence of microorganisms. The monoterpene gamma-telpinene accumulate d transiently. We conclude that anaerobic microorganisms exist that are abl e to aromatize monoterpenes with a cyclohexadiene structure. Similar biolog ical reactions may contribute to the formation of aromatic biomarker molecu les, e.g., monoaromatic steroids and hopanoids.