New microbe degrades oil into gas

Crude oil and gas naturally escape from the seabed in many places called "seeps". There, these hydrocarbons move up from source rocks to the surface through fractures and sediments, where they escape from the ground and feed a diversity of densely populated habitats in the dark ocean. The alkanes are already degraded before reaching the surface of the sediments. Even in the bottom of the sediments, where there is no oxygen, it is an important source of energy for underground microorganisms, including some archaea.

The Archaea have presented many surprises in recent years. Today, a study conducted by scientists from the Max Planck Institute of Marine Microbiology of Bremen (Germany) and the Center for Marine Environmental Sciences (MARUM) provides information on the ### 39 environment, genomes and the first images of a microbe likely to transform hydrocarbons to methane. Their results are published in the journal mbio.

Oil splitting into methane and carbon dioxide

This microbe, an archeon named Methanoliparia, transforms hydrocarbons by a process called disproportionation of alkane: it separates the oil into methane (CH₄) and carbon dioxide (CO₂) Previously, it was thought that this transformation required a complex partnership between two types of organisms, archaea and bacteria. Here, the team at the Max Planck Institute of Marine Microbiology and MARUM presents evidence of a different solution. "This is the first time we see a microbe capable of degrading oil into methane," says first author, Rafael Laso-Pérez.

During a cruise in the Gulf of Mexico, scientists took sediment samples from the Knoll Chapopote, an oil and gas infiltration located 3,000 m deep in the ocean. Back to the Bremen lab, they performed genomic analyzes that revealed that Methanoliparia is equipped with new enzymes to use the little reactive oil without having oxygen on hand. "The new body, Methanoliparia, is in a way a composite being, "says Gunter Wegener, the initiator and lead author of this study." Some of his parents are multi-carbon archaea degrading hydrocarbons, others are long-established methanogens that form methane as a metabolic product. "With the combined enzymatic tools of both parents, Methanoliparia activates and degrades the oil but forms methane as the final product. In addition, visualization of organisms supports the proposed mechanism: "Microscopy shows that Methanoliparia the cells attach to the oil droplets. We have not found any indication that bacteria or other archaea are needed as partners, "continues Wegener.

Very common and distributed worldwide

Methanogenic microorganisms have played an important role in the development of the Earth's climate because their metabolic product, methane, is an important greenhouse gas 25 times more potent than carbon dioxide. Laso-Pérez and his colleagues also wanted to know how widespread this new organization was. "We scanned DNA libraries and found that Methanoliparia is frequently detected in oil reservoirs – and only in oil reservoirs – all over the oceans. Thus, this organism could be a key agent in the transformation of long-chain hydrocarbons into methane, "said Laso-Pérez.

The scientists then want to deepen the secret life of this microbe. "We now have genomic evidence and images on broad distribution and the surprising potential of Methanoliparia. But we can not cultivate them in the laboratory yet. This will be the next step to take. This will allow us to investigate many other exciting details, "says Wegener. For example, if it is possible to reverse the process, which would ultimately allow us to transform a greenhouse gas into fuel. "