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At more than 470 times the atmospheric concentration of COâ‚‚, a humble soil bacterium does something extraordinary: it turns gas into stone.

In the future, could the walls of our houses be partly made from CO₂? Researchers from EPFL's Soils Mechanics Laboratory, the University of Applied Sciences and Arts of Southern Switzerland (SUPSI) and the EPFL start-up Medusoil SA have demonstrated that Bacillus megaterium—a resilient and versatile microorganism commonly found in soil, freshwater and marine environments or even plant surfaces—can mineralize carbon dioxide (CO₂) into calcium carbonate (CaCO₃), the mineral that forms limestone and marble. Their study has been in Scientific Reports.

What sets this study apart is not just the biological feat itself, but the quality and origin of the mineral formed. Under high-CO₂ conditions—specifically, at concentrations over 470 times those found in the atmosphere—B. megaterium shifted its metabolic strategy. Using an enzyme called carbonic anhydrase, it converted CO₂ into bicarbonate, which then reacted with calcium ions to form solid calcite. Astonishingly, 94% of the resulting mineral was derived directly from CO₂, not from nitrogen-based compounds like urea.

A clean route to solid minerals

"We know that dozens of bacteria have the potential to mineralize crystals," says Dimitrios Terzis, corresponding author, Research and Teaching associate at EPFL's Soil Mechanics Laboratory and co-founder of Medusoil SA. "However, what is unique about our work is that we showcase this can be done by directly using COâ‚‚. The potential that lies ahead is huge, and our teams can't wait to upscale and maximize it."

This biological duality is rare. B. megaterium possesses two metabolic pathways to induce mineral formation: ureolysis, which depends on nitrogen compounds, and carbonic anhydrase activity, which uses CO₂ directly. While the former has long been studied in the context of microbially induced calcite precipitation (MICP), it produces unwanted byproducts such as ammonia. The latter, by contrast, offers a cleaner route—capturing CO₂ and converting it into a solid mineral without toxic residues.

"This study shows how environmental microbiology, when combined with advanced laboratory techniques, can reveal mechanisms that would otherwise remain hidden" says Pamela Principi, researcher at SUPSI. "The use of C¹³-labeled urea was key to tracing the origin of the carbon in the mineral, allowing us to quantify the microbial pathways with precision. It's a great example of how multidisciplinary approaches—bridging microbiology, geochemistry, and materials science—can lead to impactful discoveries."

Small microbes, big potential

As conversations about climate action shift from carbon offsetting to emission prevention at the source, this research points to a new path forward—especially for industries like construction and materials manufacturing, which are among the largest direct emitters of greenhouse gases. By embedding carbon into mineral form, this microbe opens the door to bio-based, carbon-sequestering binders, and even conservation-grade materials for building and monument restoration.

This natural mechanism offers a tangible way to harness biology for climate-positive outcomes, such as capturing CO₂ at emission points, stabilizing soils or enhancing the durability of infrastructure. "Medusoil has the know-how to operate bioreactors and scale up microbial production with field-ready solutions," says Dimitrios Terzis.

"This study shows that despite challenges like the high concentration of COâ‚‚ needed and the fact we have to vary its purity levels, critical parameters can be effectively controlled using conventional biotechnology. We're confident we can tune our recipes and growth conditions to bring B. megaterium to industrial deployment."