The project

The global fashion industry is continually adopting new materials but has only recently begun to consider developing materials with sustainability in mind. In parallel, researchers in synthetic biology have started to turn their expertise in genetic reprogramming to engineer microorganisms to produce materials with new properties and functions. It would be ideal for these two new trends to meet. For over a decade, we have worked on engineering the Gram-negative bacterium Komagataeibacter rhaeticus, which produces copious amounts of bacterial cellulose — a linear, unbranched polysaccharide consisting of β-1,4-glucopyranose units. This vegan, biodegradable leather substitute can be grown under simple oxidative fermentation conditions1,2. After meeting with a designer from the fashion industry, we began a collaboration to engineer a K. rhaeticus strain that can make a sustainable material for fashion with features only possible through synthetic biology.

The solution

It was already established that bacterial cellulose makes an excellent vegan, biodegradable alternative to leather, so we looked downstream of material production for inspiration on aspects that could be enhanced using genetic engineering. We focused on two aspects: coloring the material and patterning it. Leather handbags that are black and have a pattern on them are sold in the millions, but the process of dyeing leather black and patterning it is heavily polluting and energy intensive. However, animals and plants naturally produce black and patterned materials, suggesting that synthetic biology could also accomplish these steps.

To meet this challenge, we first engineered a K. rhaeticus strain to express the coding sequence of Tyr1, a tyrosinase enzyme from Bacillus megaterium, so that this strain can convert tyrosine into eumelanin, the same pigment that gives feathers, hair, skin and eyes their black color. However, because K. rhaeticus acidifies the medium during growth whereas melanin production is inefficient in these conditions, we optimized pellicle and pigment production by implementing a two-step protocol. In the growth step, cells efficiently produced tyrosinase as they grew cellulose layers, and then during the subsequent enzymatic reaction, the cells produced a colorfast black pigment that stained the cellulose naturally (Fig. 1). We next optimized an engineered system for optogenetics3 for the Tyr1-expressing K. rhaeticus, allowing us to project light patterns onto growing cultures that trigger cells to produce melanin in patterns as they make the material. This system worked well for inducing bacteria in the material to produce fluorescent proteins in millimeter-scale patterns but has proved difficult to interface with the tyrosinase–eumelanin production system. Consequently, precise black and white patterns have eluded us but should be achievable with further optimization.

Fig. 1: Production of black melanated cellulose by engineered bacteria.
figure 1

a,b, K. rhaeticus engineered to express tyrosinase does not produce the pigment melanin in normal growth conditions (mel–) but accumulates melanin when grown in melanin-promoting conditions (mel+), resulting in cellulose pellicles that are then black. c, The black cellulose pellicles are colorfast and can be dried and pressed into microbial leather products, such as the wallet depicted here. ptyr1, plasmid-encoded tyrosinase 1. © 2024, Walker, K. T. et al., CCBY 4.0.

Full size image

Future directions

Being able to genetically program the color of a textile or fabric could remove the need for the entire dyeing step in the fashion industry, with huge sustainability benefits. In nature, pigment production occurs in situ during material growth, so it makes sense to emulate this approach.

However, self-dyeing and easy programmable patterning are not attainable yet. The light-induced patterning of pigment needs to be optimized, and achieving growth and pigmentation in a single step would be more efficient and scalable than our current two-step process. Thus, identifying a melanin-producing tyrosinase enzyme that is active at the low pH needed for cellulose growth is a priority.

To solve these problems and make self-dyed, patterned black and white bacterial cellulose a reality in the near future, we have set up collaborations. A team at Northumbria University, UK, is testing acid-tolerant tyrosinases to help us attain a one-step process, and another group at Imperial College London is exploring engineered genetic networks for Turing pattern formation4. Our group is looking at the possibility of expressing other pigments to expand the available color palette, and we are also investigating ways to improve the optogenetics system. Finally, a London-based startup company has been part of this project from the start and is working to bring bacterial cellulose-based materials to customers in the fashion industry, which will hopefully result in some useful, sustainable, microbe-engineered products soon being available to consumers.

Tom Ellis & Kenneth Walker

Department of Bioengineering, Imperial College London, London, UK.

Expert opinion

“This work is an important advance in engineered materials because it represents the first example of a genetically engineered organism that can produce pigmented textile materials. Self-dyeing fabrics will forgo the need for fabric dyes, dramatically improving the efficiency and environmental impact of the textile industry. This new technology could also permit new types of fabrics that display different colors based on the environmental conditions when they were produced or display color patterns specified simply by shining patterned light.” Anne S. Meyer, University of Rochester, Rochester, NY, USA.

Behind the paper

The catalyst for this project was our involvement in a biodesign class for the MA Material Futures course at Central St Martins (University of the Arts, London), where we showed students some synthetic biology and advised them on project ideas. This endeavor made us look beyond traditional biotech application areas. A student in this course, Jen Keane, began collaborating with us informally on using bacterial cellulose as a high-performance textile. Her innovative work pushed us to look at ways to enhance microbial leather by engineering the bacteria that grow the material. The collaboration led to many fun, tricky experiments at much greater scales than our usual work, and to producing items to be used in the real world. As we worked on the science, Jen and an ex-member of our group founded a startup company to bring bacterial cellulose products to market. K.W. & T.E.

From the editor

“Here the authors use genetic tools to engineer the bacterium K. rhaeticus to produce a black pigment, which becomes incorporated into the bacterial cellulose materials. This could be useful when scaled up for various textile applications.” Editorial Team, Nature Biotechnology.