Mushrooms and bacteria constructing buildings may sound like something out of science fiction. However, this time, American scientists have utilized these microorganisms to create self-mineralizing and self-repairing building materials, which not only have the potential to replace some concrete but also make the idea of microbes helping us build houses a reality.
In the past, scientists have induced some microorganisms to achieve Microbially Induced Calcium Carbonate Precipitation (MICP), transforming them into promising Engineered Living Materials (ELM) for constructing or repairing simple load-bearing structures. Although some ELM materials have successfully entered the commercial market, their acceptance is not high.
The reason is that ELM materials have a short lifespan and require specific storage conditions to extend their longevity, among other issues. Additionally, at this stage, these materials are still challenging to repair complex internal building structures, which limits their potential applications and benefits.
This time, an experimental team from Montana State University in the United States has cultivated dense sponge-like fungal mycelium made from Bacillus pasteurii and Neurospora crassa, creating a living, self-repairing building material. Their research results were published on April 16 in the journal “Cell Press”.
The Bacillus pasteurii selected by the researchers is a common alkaliphilic bacterium in the soil, with minimal environmental impact and non-pathogenic characteristics, capable of mineralizing with the uptake of nutrients and calcium ions. Similarly, Neurospora crassa, also known as the pink bread mold, is non-pathogenic, rapidly grows mycelium, and has the ability for MICP induced by urea decomposition.
The researchers introduced the Bacillus pasteurii, capable of producing calcium carbonate (found in corals, eggshells, and limestone) into the fungal mycelium framework grown by Neurospora crassa. The Bacillus pasteurii then continues its biomineralization process inside, gradually hardening the originally flexible mycelium into a solid structure with significantly increased hardness. (The mycelium framework can self-mineralize, and the mycelium framework is effectively biomineralized by urine-degrading bacteria)
Moreover, they found that the engineered living materials developed could maintain over four weeks of biological activity even in a dry environment at temperatures ranging from 23°C to 30°C, longer than other types of engineered living materials. This contributes to creating excellent engineered living materials.
The researchers used a scanning electron microscope with energy-dispersive spectroscopy (SEM-EDS) to observe the appearance of the mineralized mycelium framework. The results showed that Bacillus pasteurii, after metabolizing urea (the bacteria’s food), produces calcium carbonate, and these mineral crystals gradually integrate into the mycelium, further reinforcing the density and stability of the entire mycelium framework.
To validate the practicality of this biomineralization ELM material, the team placed it in a mold with complex cavities. The results showed that these biomineralization frameworks grew in concentric rings, eventually filling the internal voids of the mold, showcasing the excellent repair capability of the material.
They also stated that although the potential of fungal mycelium as biomineralization ELM has been confirmed, challenges such as the inability to co-cultivate two microorganisms and the need to optimize the material’s mechanical properties remain. They will continue researching to address these issues and promote large-scale production of the material to replace some high-energy-consuming building materials and reduce environmental pollution.
One of the main authors of the experiment, Chelsea Heveran, an assistant professor at Montana State University and corresponding author, stated, “Previously, the strength of biomineralization materials was insufficient to completely replace concrete. However, we and others are working to improve their performance to expand their future applications.”
Heveran also mentioned, “We have found that fungal frameworks are very useful for controlling the internal structure of materials. Now that we have successfully created inner geometric structures similar to cortical bone (concentric circles), we hope to develop more geometric structures in the future for optimizing the internal structures of other materials.”