Archaea are a domain of prokaryotic single-celled organisms. They are numerous in the ocean, with plankton being one of the most abundant groups. They also exist in sediment deep in the ocean. These organisms feed off hydrocarbons from oil and gas seeps in the seabed.

An archaea, Methanoliparia, transforms hydrocarbons by a process called alkane disproportionation. In this process, oil is split into methane (CH4) and carbon dioxide (CO2). Previously, this transformation was thought to require a complex partnership between archaea and bacteria. More specifically, anaerobic oxidation of methane (AOM) is performed by anaerobic methanotrophic archaea (ANME) by reverse methanogenesis pathway to oxidize methane and is then coupled with sulfate reduction by bacteria, often of the Deltaproteobacteria class.

However, research has suggested that “Ca. Methanoliparia” archaea may perform alkane degradation coupled with methanogenesis in a single organism. The Max Plank Institute researchers set out to determine the role of archaea in the anaerobic degradation of non-methane alkanes in deep-sea oil seeps from the Gulf of Mexico.

The team found that Methanoliparia is equipped with novel enzymes to use the quite unreactive oil without having oxygen at hand. Metagenomic analysis of Methanoliparia revealed that they encode a complete methanogenesis pathway including a canonical methyl-coenzyme M reductase (MCR) but also a highly divergent MCR related to those of alkane-degrading archaea and pathways for the oxidation of long-chain alkyl units. These two phylogenetically different MCRs that may allow this organism to thrive as a methanogen on a substrate of long-chain alkanes.

The genomic data for Methanoliparia was compared to DNA-libraries and found that these organisms are detected in deep petroleum reservoirs, oil seeps, and oily sediment. Epifluorescence micrographs showed that Methanoliparia attach to oil droplets. The researchers concluded that Methanoliparia is frequently detected in oil reservoirs and may be a key agent in the transformation of long-chain alkanes to methane. In short, these archaea may be a key player in independent oil degradation. According to Gunter Wegener, senior author of the study, wants to “investigate many more exciting details. For example, whether it is possible to reverse the process, which would ultimately allow us to transform a greenhouse gas into fuel."

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