Can carbon dioxide (CO₂) be turned back into fuel? Since the 1990s, various efforts have been underway to find a cheap and efficient way to recycle the greenhouse gas carbon dioxide back into hydrocarbon fuels that can be used by communities. About ten years ago, the predominant thinking regarding CO₂ was that it should be buried. However, this pattern of thought has changed, as it would make more financial sense to efficiently convert it into something that can be used. Scientists discovered that CO₂, water, sunlight and an appropriate catalyst could be used to generate an alcoholic fuel.

Despite this ground-breaking research, it appears that deep-sea microbes have been doing this same reaction for many years.

Why Microbes Are Special

Humans and other animals can only utilize fats, carbohydrates and proteins for food. However, microbes are different in that they are able to break down almost any substance to produce energy. Deep sea microbes, who live in harsh environments, have become specialists in the field of using what they can, and are able to turn substances considered to be toxic by humans into energy.

Researchers from Germany have now discovered deep sea microbes that are able to convert methane and ethane – the main components found in natural gas – into CO₂ and other by-products. They can also reverse this process by turning CO₂ back into fuel. Despite the reputation of microbes to utilize various substances for food and energy production, this is the first time it was found that a deep sea microbe can break down ethane. The discovery that these microbes can turn CO₂ back into ethane implies that a closed carbon loop can potentially be created.

The Discovery

Researchers from the Max Planck Institute for Marine Microbiology and the Center for Marine Environmental Sciences (MARUM), in Bremen, Germany discovered this new species of archaea – a type of single celled organism without a defined nucleus. The microbe was found at a depth of 2000 meters, surrounding a deep sea hydrothermal vent in the Guaymas Basin, in the Gulf of California, where the microbes were using ethane seeping from the hot vents to produce energy. Most microbes are able to produce their food without help. However, several species of archaea join forces with bacteria to form a microbial consortium, which is able to break down and share a wide range of potential food, including breaking down the two main components of natural gas – methane and ethane. The newly discovered species of archaea has teamed up with a fairly common bacterial counterpart which helps to break down methane. However, the archaea itself is the first microbe that has been witnessed to break down ethane by itself. The archaea species therefore breaks down the natural gas, while the bacteria couples the electrons released in the process to sulfate. The researchers aptly named this new species of archaea Ethanoperedens thermophilum, which means “heat-loving ethane-eater”. Their findings were published in the journal mBio in April 2020.

The samples collected at the hydrothermal vent were taken to a laboratory at the Max Planck Institute to reproduce the microbial consortium. This is tedious lab work, as consortia like this take a long time to reproduce, and it is important that enough biomass is cultured to allow for testing. To the surprise of the researchers, the new archaea species reproduced quickly compared to other microbial consortia, multiplying cells over weeks instead of months, so the researchers could quickly begin performing tests.

The fast reproduction rate of the microbial consortium also implies that the microbes are well suited for being used at an industrial scale. The microbes are thus an exceptionally valuable find for these reasons – they can break down methane and ethane (which is a valuable biochemical process), they can reproduce fast, and they can potentially be used at an industrial scale. Apart from observing their ethane-eating abilities, scientists were also able to present the first complete genome of a natural gas-degrading archaea.

Reversible Chemical Reactions

There is no doubt the new archaea species is important due to them being able to break down ethane into CO₂, however they became even more crucial when the researchers realized this process can be reversible. In addition to feeding on ethane and methane and producing CO₂ and other by-products, the laboratory-grown cultures were also able to convert the greenhouse gas back into ethane, and the researchers suspect that relatives of the newly identified Ethanoperedens could naturally produce ethane from CO₂. The team is now searching for these organisms in the wild. The scientists are still unclear on the exact mechanism of this reversible reaction, however the implications of this discovery are massive. If utilized correctly, these microbes will be able to turn CO₂ back into ethane fuel at an industrial scale, creating a closed carbon loop where no additional greenhouse gasses enter the atmosphere. Although this closed carbon loop is not the best solution to combat climate change due to greenhouse gas emissions – as the use of the fuel does not remove CO₂ from the atmosphere – it is a novel concept to study and explore further in the ongoing fight against climate change, and can potentially be used to limit carbon emissions from various pollution sources.

Smallest Lifeforms With The Biggest Value

Gunter Wegener, one of the authors of the paper, was quoted in a press release saying “We shouldn’t underestimate the smallest inhabitants of the sea!”. Despite their small size and simple structures, there is still much to be discovered about microbial life – especially in the deep sea – and what they can offer. Not only are microbes useful to humans, they also play a key role in their ecosystems. In deep sea ecosystems, they are able to convert inaccessible toxic substances into bioavailable energy, which in turn supports a vast, complex and diverse community. Microbes such as single-celled phytoplankton also provide energy for creatures at the surface of the sea, as well as producing the oxygen we breathe. It is safe to assume that without these small lifeforms, life on Earth would look very different.