Anaerobic Formation of the Aromatic Hydrocarbon p-Cymene from Monoterpenes by Methanogenic Enrichment Cultures
The fate of monoterpenes in methanogenic habitats was investigated in enrichment cultures using defined mineral media inoculated with activated sludge and R-(-) -alpha-phellandrene, (+)-2-carene, (-)-alpha-pinene, or (+)-sabinene. The anaerobic biodegradation of alpha-pinene and 2-carene supported methanogenesis. In contrast, consumption of alpha-phellandrene and sabinene was accompanied by formation of the aromatic hydrocarbon p-cymene. This aromatization reaction did not occur in pasteurized or autoclaved cultures or in the absence of microorganisms. The monoterpene gamma-terpinene accumulated transiently. We conclude that anaerobic microorganisms exist that are able to aromatize monoterpenes with a cyclohexadiene structure. Similar biological reactions may contribute to the formation of aromatic biomarker molecules, e.g., monoaromatic steroids and hopanoids.
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