In a recent study published in Scientific Reports, a research team of the Department of Environment Construction and Design at SUPSI, the Swiss Federal Institute of Technology in Lausanne (EPFL) and the start-up Medusoil SA (an EPFL spin-off) demonstrated that Bacillus megaterium, a hardy and versatile microorganism commonly found in soil, fresh and sea water, as well as on plant surfaces - is able to mineralise carbon dioxide (CO₂), turning it into calcium carbonate (CaCO₃), the mineral that makes up limestone and marble.
What distinguishes this study is not only the biological result itself, but also the quality and origin of the mineral produced. In the presence of high concentrations of CO₂, more than 470 times higher than atmospheric concentrations, B. megaterium changes its metabolic strategy. Thanks to an enzyme called carbonic anhydrase, the microorganism converts CO₂ into bicarbonate, which in turn reacts with calcium ions to form solid calcite. Remarkably, 94% of the mineral obtained comes directly from CO₂, and not from nitrogen compounds such as urea.
"We know that dozens of bacteria have the potential to generate mineral crystals," says Dr Dimitrios Terzis, corresponding author of the study, researcher and lecturer at EPFL as well as co-founder of the startup Medusoil SA. "What makes our work really unique is that we have shown that this process can take place using CO₂ directly. The potential is enormous, and the Medusoil and SUPSI teams are eager to take this system to industrial scale.
This metabolic duplicity is rare. In fact, B. megaterium has two different routes to induce mineral formation: ureolysis, based on nitrogen compounds, and carbonic anhydrase activity, which directly exploits CO₂. Although the former is widely documented in the context of microbial precipitation of calcite (MICP), it involves the production of undesirable by-products such as ammonia. The second route, in contrast, represents a cleaner alternative: it captures CO₂ and transforms it into a solid mineral without generating toxic residues.
"This study demonstrates how environmental biotechnology, by exploiting state-of-the-art laboratory techniques, can help to harness microbial mechanisms that are known to exist but have remained largely unused," says Dr Pamela Principi, microbiologist and Head of Environmental Biotechnology at the SUPSI Microbiology Institute (Department of Environment Construction and Design). 'Using C13-labelled urea, we were able to precisely trace the origin of the carbon in the mineral, allowing us to precisely quantify the metabolic pathway. This is an excellent example of how multidisciplinary approaches, combining biotechnology, geochemistry and materials science, can lead to high-impact discoveries."
The implications are profound. As the debate on climate action shifts from offsetting emissions to preventing them at source, this research opens up new avenues for sectors such as construction and materials production, among the largest direct emitters of greenhouse gases. By incorporating carbon in mineral form, this micro-organism opens the way to bio-based binders capable of sequestering CO₂, to materials suitable for the conservation and restoration of buildings and monuments.
From capturing CO₂ at emission points to stabilising soils and enhancing the durability of infrastructure, this natural mechanism offers a real opportunity to harness climate-friendly biology. And with protocols now available to control and optimise microbial behaviour, the door is open to large-scale industrial application.