Engineers from MIT and Imperial College London have developed a new way to produce tough, functional materials using a mixture of bacteria and yeast, similar to the “kombucha mother” used to ferment tea.
Also called SCOBY (symbiotic culture of bacteria and yeast), the researchers were able to produce cellulose embedded with enzymes that can perform a variety of functions, such as detecting environmental pollutants. They also showed that they could incorporate yeast directly into the material, creating ‘living materials’ that could be used to purify water or create ‘smart’ packaging materials that can detect damage.
“We envision a future where diverse materials can be grown at home or in local manufacturing facilities, using biology rather than resource-intensive centralized manufacturing,” said Timothy Lu, an MIT associate professor of electrical and computer science and biological engineering.
Lu and Tom Ellis, a professor of bio-engineering at Imperial College London, are the senior authors of the paper, which appears today in Natural materials. The paper’s lead authors are Tzu-Chieh Tang, a graduate of MIT and postdoctoral fellow Charlie Gilbert at Cambridge University.
Division of labor
Several years ago, Lu’s lab developed a way to use E coli to generate biofilms embedded with materials such as gold nanowires. However, these films are very small and thin, making them difficult to use in most large-scale applications. In the new study, the researchers set out to find a way to use microbes to generate larger amounts of more substantial materials.
They thought of creating a microbe population similar to a kombucha mother, which is a mixture of certain types of bacteria and yeast. These fermentation plants, which usually contain one strain of bacteria and one or more yeasts, produce ethanol, cellulose and acetic acid, giving kombucha tea its distinctive flavor.
Most wild yeast strains used for fermentation are difficult to genetically modify, so the researchers replaced them with a strain of lab yeast called Saccharomyces cerevisiae. They combined the yeast with a type of bacteria called Komagataeibacter rhaeticus, who had previously isolated their staff at Imperial College London from a kombucha mother. This species can produce large amounts of cellulose.
Because the researchers used a lab yeast, they were able to design the cells to do all the things that lab yeast can do – for example, produce enzymes that glow in the dark or detect environmental pollutants. The yeast can also be programmed to break down pollutants after they are detected.
Meanwhile, the bacteria in the culture produce tough cellulose on a large scale to serve as scaffolding. The researchers designed their system so that they can check whether the yeast itself, or only the enzymes they produce, are included in the cellulose structure. It only takes a few days for the material to grow, and if left long enough it can thicken to take up a space the size of a bathtub.
“We think this is a good system that is very cheap and very easy to make in very large quantities,” says Tang. “It’s at least a thousand times more material than the E coli system.”
Just add tea
To demonstrate the potential of their microbe culture, which they call “Syn-SCOBY,” the researchers created a material with yeast that detects estradiol, which is sometimes found as an environmental pollutant. In another version, they used a yeast strain that produces a glowing protein called luciferase when exposed to blue light. These yeasts can be replaced with other strains that detect other pollutants, metals or pathogens.
The culture can be grown in normal yeast culture medium, which the researchers used for most of their studies, but they have also shown that it can grow in tea with sugar. The researchers envision that the cultures could be adapted so that people could use them at home for growing water filters or other useful materials.
“Pretty much anyone can do this in the kitchen or at home,” says Tang. “You don’t have to be an expert. You just need sugar, you need tea to get the nutrients, and you need a piece of Syn-SCOBY mother. “
The research was funded in part by the US Army Research Office, the MIT Institute for Soldier Nanotechnologies, and the MIT-MISTI MIT-Imperial College London Seed Fund. Tang was supported by the MIT J-WAFS Fellowship.