Non-syntrophic methanogenic hydrocarbon degradation by an archaeal species

The methanogenic degradation of oil hydrocarbons can proceed through syntrophic partnerships of hydrocarbon-degrading bacteria and methanogenic archaea 1 – 3 . However, recent culture-independent studies have suggested that the archaeon ‘ Candidatus Methanoliparum’ alone can combine the degradation of long-chain alkanes with methanogenesis 4 , 5 . Here we cultured Ca . Methanoliparum from a subsurface oil reservoir. Molecular analyses revealed that Ca . Methanoliparum contains and overexpresses genes encoding alkyl-coenzyme M reductases and methyl-coenzyme M reductases, the marker genes for archaeal multicarbon alkane and methane metabolism. Incubation experiments with different substrates and mass spectrometric detection of coenzyme-M-bound intermediates confirm that Ca . Methanoliparum thrives not only on a variety of long-chain alkanes, but also on n -alkylcyclohexanes and n -alkylbenzenes with long n -alkyl (C ≥13 ) moieties. By contrast, short-chain alkanes (such as ethane to octane) or aromatics with short alkyl chains (C ≤12 ) were not consumed. The wide distribution of Ca . Methanoliparum 4 – 6 in oil-rich environments indicates that this alkylotrophic methanogen may have a crucial role in the transformation of hydrocarbons into methane. ‘Candidatus Methanoliparum’ overexpresses genes encoding alkyl-coenzyme M and methyl-coenzyme M reductases—markers of archaeal multicarbon alkane and methane metabolism—and thrives on a variety of long-chain alkanes and n -alkylcyclohexanes, and n -alkylbenzenes with long n -alkyl (C ≥13 ) moieties.