Living mini factories
e live in a dilemma. The resources of our planet Earth are limited. Yet people's hunger for raw materials remains unchecked and insatiable. What can we do? In order to replace unsustainable methods of extracting materials with more environmentally friendly alternatives, microorganisms could be used to produce a range of unique materials, including cellulose, silk or minerals, among other things. The research group led by André Studart, Professor of Complex Materials at ETH Zurich, has now presented a new approach in this direction. By specifically accelerating evolutionary processes using UV light, the researchers have found a way to transform bacteria into living mini-factories. The study was published in the scientific journal PNAS.
With accelerating climate change, the sustainable production of materials is more important than ever. In contrast to the energy-intensive processes employed to fabricate most synthetic materials, some materials such as cellulose, silk, or minerals are naturally produced by microorganisms in water and ambient temperature. However, this takes a long time, and it is too little for industrial quantities. Therefore, most of the raw materials we use are mined in a not very environmentally friendly way. A prominent example is cellulose film, also known as cellophane. This is mainly made from cellulose, which is extracted from cellulose pulp.
The new technique developed by André Studart's team now offers a way to boost organic production in the cellulose-producing bacterium Komagataeibacter sucrofermentans. “We tried to accelerate the evolution of this bacteria in the lab, as a result we can use them as mini factories and then have many, many of them to produce a material that then we can use. And that is also a very sustainable material” said Julie Laurent first author of the study and doctoral student in Studart's group.
Bacterial cellulose in the wet state. Photo: Peter Rüegg / ETH Zurich
To create these mini factories, Julie Laurent radiated the native microorganism with UV-C light to damage part of the cell’s DNA. She then placed them in a dark room to force mutations. “Since a lot of the DNA repair mechanisms of the cells are light dependent, if you put them in the dark, they don't have those repair mechanisms anymore and the cells become really stressed and ultimately mutate” explains Julie. In other words, the bacteria cells are put under stress, forcing them to adapt and mutate under extreme circumstances emulating natural evolution. “We chose UV-C light because is an easy, universal very general method” says Julie. “If you target the whole genome, then there are millions and millions of mutagenesis possibilities. And it enables you do it on any microorganism, without the need to know the genome.”
After the bacterial cells mutate, a library of different mutants is created, similar to a mixed bag of jellybeans. To examine the individual cells, each one is encapsulated in a tiny droplet of nutrient solution and a special dye that “attaches” itself to the cellulose. After an incubation period, where the cell is allowed to grow and produce cellulose, they are passed through a screening process. Through an electric field the cells that produce more than others are separated. The overproducing cells can be recognized because they “glow” strongly than the others. “We screened 40,000 single bacteria, and we selected 500. So, in the sorting process, we selected the 1.24%, then I just chose five of them” told us Julie.
The five variants were used to analyze which genes had been altered by the UV-C light and how these changes lead to the overproduction of cellulose. Of the five selected bacteria, four showed an overproduction of cellulose. These producers had the same mutation in the same gene, leading the researchers to hypothesize that this gene may be involved in regulating cellulose production. This is a significant advance in understanding how bacteria produce organic materials.
Julie Laurent is now looking at the properties of the cellulose, to determine whether the cellulose produced by the native strain and the mutation have the same properties. The researchers believe that the promising results of the study could also be used for other microorganisms in the future.
The mini factories present an important step towards the sustainable production of materials, and could represent a milestone in this field, the researchers write. They envision a future where various interdisciplinary approaches will come together to develop materials in a sustainable and environmentally friendly manner, of course with the living mini factories as one of them.
Original Publication:
Laurent JM, Jain A, Kan A, Steinacher M, Enrriquez Casimiro N, Stavrakis S, deMello AJ, Studart AR.
Directed evolution of material-producing microorganisms
Proc Natl Acad Sci, 23 Jul 2024
doi.org/10.1073/pnas.2403585121
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