Ants capture carbon dioxide from the air and turn it into armor

An ant that can turn carbon dioxide in the air into dolomite rock in its exoskeleton may hold clues to how humans can sequester greenhouse gases to avert climate catastrophe.

Mushroom-growing ants forage for vegetation to feed the cultivated fungi that grow in their colonies. Mushrooms, in turn, serve as the primary food source for ants. High densities of ants and fungi can result in high concentrations of CO2 inside the nests.

in 2020 Cameron Currie at the University of Wisconsin-Madison and his colleagues found that ants of this species Acromyrmex echinatior incorporate a carbonate biomineral into their armor. Ants do this through a symbiotic relationship with Pseudonocardia bacteria that convert CO2 into rock using chemical processes that are not yet well understood.

Now the team discovered that another mushroom-growing ant, Sericomyrmex amabilisfound in Central and South America, can do the same without symbiotic bacteria, becoming the first known animal to have evolved this ability.

Remarkably, the mineral they produce is dolomite, which is extremely difficult for chemists to produce in the laboratory. Dolomite rocks such as those found in the Italian Dolomites require millions of years and complex geological processes for the calcium and magnesium atoms to align perfectly. Yet the ants do it quickly and effortlessly, without high temperatures, says a member of the team Hongjie Li at Zhejiang University in China.

Dolomite is composed of calcium, magnesium and carbonate. Forming dolomite in the lab is difficult because magnesium holds tightly to surrounding water molecules and doesn’t easily fit into the calcium carbonate structure, which slows crystal formation, Currie says. To try to overcome this, scientists use high temperatures and pressures, he said. The team’s next phase of research will try to understand how ants are able to achieve this feat.

For mushroom-growing ants, turning CO2 into stone solves at least two problems: strengthening the ants’ exoskeleton and preventing toxic CO2 from building up inside the colony.

“We have discovered a natural system that has evolved over millions of years to reduce the toxic build-up of atmospheric CO2 in an ant colony,” says Currie.

In an effort to counter global warming, scientists are exploring techniques to convert atmospheric CO2 into carbonate minerals, which essentially turn carbon into stone. “These ants are the first animal shown to engage in such a process and offer exciting potential as a model for human endeavours,” says Currie.

Cody Freas at the University of Toulouse in France, who was not part of the study, describes the ants’ ability to convert CO2 into dolomite as a “remarkable adaptation.” “Individuals take on the role of living carbon sinks, converting atmospheric carbon dioxide into a protective mineral armor,” says Freas. “This dual solution helps ants regulate the nest atmosphere and create bioengineered physical defenses.”

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