A recent research paper showing that certain subterranean microbes produce surprising amounts of oxygen—even in the absence of light—may trigger a thorough overhaul of established scientific notions about underground life.
Published last month in Nature Communications, the study analyzed groundwater samples from 95 monitoring wells located 820 feet (250 meters) or more below ground level across 14 different aquifers in the fossil-fuel fields of Alberta, Canada.
The study has made waves in scientific circles with its most significant revelation, which was the discovery of an abundance of microbes capable of producing unexpectedly large amounts of oxygen in the absence of light—what the researchers call “dark oxygen.”
The production of oxygen has mostly been associated with photosynthesis: plants or cellular organisms using the energy provided by sunlight and synthesizing carbon dioxide and water to produce carbohydrates, while releasing oxygen as a by-product. This led many scientists to assume that deeper subterranean realms had to be oxygen-deficient dead zones, where only the most primitive cellular life-forms, impeded by the lack of oxygen, lived a slumbering existence—an assumption shattered by the new discoveries.
Not only do these subterranean microbes produce oxygen, the amount of oxygen they emit may very well be enough to support other oxygen-dependent life forms in the surrounding waters and soil.
The study was initiated by S. Emil Ruff, then an assistant scientist at the Department of Geoscience at the University of Calgary, Canada, in 2015. When he started his postdoctoral fellowship in microbiology, he expected the project to be sound but fairly run-of-the-mill research. The unexpected results, however, would end up keeping him and his team occupied for the next six years.
To the surprise of the research team, the older, deeper groundwaters contained more microbial life than the fresher waters did. As they started identifying the various cellular species, things didn’t add up: many were aerobes—microbes that require oxygen to sustain themselves. On further analysis, the deep groundwater was found to contain plenty of dissolved oxygen, which shouldn’t have been possible.
The unusual concentration of oxygen prompted Mr. Ruff to conclude that the examined water sample must have been contaminated. However, the oxygen content seemed consistent across all 138 samples, which raised only more questions.
The conundrum reminded professor Marc Strous, the head of the laboratory where Mr. Ruff was working, of research he conducted in the Netherlands in the late 2000s, when he discovered a type of oxygen-producing bacteria that lives in shallow lake sediments and wastewater sludge. The bacteria used enzymes to break down nitrites, releasing oxygen. It then used this oxygen to split methane molecules from the surrounding sludge for energy.
Mr. Ruff and his team decided to sequence the genomes of the entire community of microbes in the groundwater samples to see whether a similar biochemical process—called dismutation—could be determined.
Mr. Ruff’s work is already being hailed as a landmark study, defying preconceived notions about what may well be the planet’s biggest biosphere: the underground microbial world.
