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Living in a house made of fungi and bacteria may sound like the stuff of science fiction, but researchers are now one step closer to eventually making it a reality, according to a new study.Related video above: Cats go viral after Minnesota family built them a cat condoA research team in Montana grew dense, spongy tangles of mycelium — the rootlike structure that connects fungal networks underground — as a framework to create a living, self-repairing building material.The ability to create durable, load-bearing structures with living material is still many years away. However, this discovery is an important step toward creating a sustainable alternative to cement, the binding agent in concrete, said Chelsea Heveran, senior author of the study published April 16 in the journal Cell Reports Physical Science.More than 4 billion metric tons (4.4 billion tons) of cement is manufactured annually, contributing about 8% of global carbon dioxide emissions, according to London-based think tank Chatham House. This means if cement production were a country, it would rank third after China and the United States based on 2023 emissions. “We asked, ‘What if we could do it a different way using biology?’ That’s the vision,” said Heveran, who is an assistant professor of mechanical and industrial engineering at Montana State University, Bozeman.The study authors introduced bacteria capable of producing calcium carbonate — the same chemical compound found in coral, eggshells and limestone — to the fungal mycelium, which served as scaffolds. Through a process called biomineralization, the calcium carbonate hardened the gooey, flexible mycelium into a stiff, bonelike structure.“We’re not the first ones to biomineralize something and call it a building material. … But if you want to keep (the bacteria) alive for longer so that you can do more with them, there’s been some challenges involved to extend that viability,” Heveran said. “So that’s why we gave them fungal mycelium scaffolds, because the mycelium is really robust, and in nature, sometimes it biomineralizes (itself).”The team experimented with letting the fungus, called Neurospora crassa, biomineralize on its own but found that killing it and then adding the microbes helped achieve a stiffer material in less time. The bacteria, called Sporosarcina pasteurii, created crystalline nets of calcium carbonate around the fungal threads after metabolizing urea, which is like food for the bacteria.While other biomineralized building materials are only considered “living” for a few days, Heveran said her team was able to keep the microbes active for at least four weeks, and eventually, that period could extend to months or even years.“We’re really excited in our next work to ask the questions ‘could we seal a crack in the material?’ Or ‘could we sense something using these bacteria?’ Like, imagine you had poor air quality in your building, and these bricks were your walls. Could they light up to (indicate) that?” Heveran said. “Before, we couldn’t do any of that because the microbes weren’t alive enough, but they’re very alive now.”There’s still mush-room for improvementBefore being used for homes, fences or other construction, a lot more testing is needed to find a living building material to replace cement, said Avinash Manjula-Basavanna, a bioengineer who was not involved in the study.“These kinds of experiments are done on a small scale. … They are not necessarily a reflection of the bulk material properties,” said Manjula-Basavanna, who is a senior research scientist at Northeastern University in Boston. “It’s not stiffness that people are interested in when it comes to construction materials. It is the strength, (the) load-bearing ability.”While the strength and durability of living building materials is not on par with concrete yet, Heveran said mycelium is still a promising base. Thanks to its flexibility, the sticky substance could be shaped to include vascular-like channels within beams, bricks or walls.Much like blood vessels in the human body, cells within living building materials need structures capable of delivering nutrients to stay alive. However, adding these structures into the design of building materials could make them weaker, presenting a challenge for future studies, Manjula-Basavanna said.“I think in the future, they could be useful for single-story buildings, these smaller structures — it’s very much feasible,” Manjula-Basavanna said. “It might be five to 10 years down the line.”Fungus is also a potential respiratory hazard, and though killing the mycelium reduces its allergen-producing ability, more research should be done before it’s considered safe to inhabit, Heveran said.“It’s very clear to conceptualize a test framework by which the materials need to be strong enough, because those kinds of standards exist already,” Heveran said. “But we don’t have regulatory standards for my bricks that have cells in them.”Looking aheadIt’s safe to say you won’t see fungus bricks sold at your local home improvement store any time soon.Heveran’s team is just one of many in the country exploring the possibilities of mycelium, which has been used for other, softer items such as packaging and insulation.Several government agencies are already interested in the possible use cases of living building materials, Heveran said.“There’s a lot of ‘ifs’ that would have to come into play for the average household to have a cost benefit from this,” Heveran said.“But for society, it might be a lot cheaper when you’re trying to build infrastructure for a community that really needs it, or if you’re trying to build infrastructure in space, this might be a lot easier than carting cement and concrete up there,” she explained. “The possibilities are really exciting to me.”