Engineering bacteria to grow a leather that dyes itself black

In a collaboration with Jen Keane at Modern Synthesis work led by Marcus Walker and our group has developed genetically engineered bacteria that can grow a microbial leather that dyes itself black. This important new Engineered Living Materials work has recently been published in Nature Biotechnology.​​

In our work on engineered living materials, a question we often ask ourselves is ‘How can we use synthetic biology to make materials more sustainable?’ Our favourite bugs for making ELMs are kombucha bacteria, which can very efficiently make an off-white bacterial cellulose material at scale that has great promise as a biodegradable textile for the fashion and accessories industry, especially as a vegan alternative leather. We’ve shown before that these bugs can be reprogrammed with DNA parts and synthetic biology tools. Our default has always been to add fancy new functionalities to the cells, like spatial sensing and enzymatic action, to get them to grow advanced materials.

But if bacterial cellulose is a candidate to replace leather, Marcus wondered whether we can do something simple with our genetic engineering that could have a big impact. He rose to this challenge in his PhD by tackling perhaps the most polluting step of the textiles industry; fabric dyeing. Textiles are dyed with harsh chemicals with often uncontrolled release of polluted water into the environment. A black wool coat will typically be made with pure white wool that is put through several stages of colouring with organic chemicals like the azo dye, Acid Black I.

From a biology point of view, this is madness. A black sheep has black wool not due to dyeing, but because it expresses genes in the cells that are making fibres and these genes encode enzymes that produce and deposit pigments into the wool as it gets made. Far more efficient! Marcus was inspired this observation, and so sought to make his own ‘Bacterial Black Sheep’ to demonstrate that the powers of biotechnology can be used to remove this polluting step that is such a barrier for sustainability in the textiles industry.

His chosen colour was black; the most important colour in the textiles industry and one of the hardest to achieve with natural dyes. His pigment for this was melanin, the near-ubiquitous pigment used by nature to make all things black like crows and hair. (Eu)melanin can be made in bacteria via the expression of just one enzyme - tyrosinase. This converts tyrosine into dopachrome which eventually polymerises and aggregates to make black pigment that can bind tightly among cellulose fibres, like in sheep wool. Engineered expression of tyrosinase in our K. rhaeticus cells literally turns them black when pH is above 7. Below this, the cells still produce copious amounts of material, while loading up with lots of enzyme ready for the pH change that triggers our colour-production stage. This gives us a way to grow stunning black textile materials, and even tune the shade of pigment too. It doesn’t interfere at all with material growth and the scale-up methods for bacterial cellulose textiles, and retains the full colour when sterilised and taken from the lab.

​To demonstrate this working at a scale suitable for textiles and fashion we worked closely with Jen Keane, who went on to found Modern Synthesis a start-up known for their innovative ‘microbial weaving’ approach for growing sustainable materials that make a biodegradable shoe. With Jen’s help we used our black sheep bacteria to grow the upper for a black shoe, which she exhibited with the title ‘This is GMO’ to make people think about what could be possible if we can use biotechnology to replace unsustainable practices in the fashion industry. We believe this was the first case of a textile being made by an organism genetically engineered to self-pigment the material to a specific chosen colour. 

Both the material and the self-dyeing are very robust: black material samples we’ve made years ago are still black as ever after wear-and-tear and still have that crazy strength that bacterial cellulose has due to its long pure interwoven fibres.

But as cool as jet-black is, it seems a lot of people want patterns and lots of logos on their fashion items. 🤷 So can we also do something for this?

This is where we went a bit more ‘fancy synbio’ with the research. Marcus took a synthetic system for optogenetic control of gene expression built from E. coli and fine-tuned this to work in our cells. By developing smart projection methods, he could precisely control which cells in a growing textile sheet are turning on target gene expression.

This was all done with red fluorescent protein (RFP) production used as the reporter for gene expression and gives us amazing images of petri-dish scale materials which glow with red fluorescent logos and sub-mm scale features. Super cool. Swapping RFP for the melanin-making tyrosinase should allow us to project light onto a growing culture and this then develop as black logos on a white material background. It sort-of-works, but definitely needs optimisation. As a proof-of-principle it shows us what is possible.

Patterning is for the future, but we believe self-dyeing is scalable now. Bacterial cellulose is already far more sustainable to make than leather and is biodegradable too. By using synthetic biology to self-dye the material we can solve another key step in its sustainability.👍

This research was mostly funded by UKRI EPSRC, and done with the help of Ivy Li and advice of Viv Goosens and several other great colleagues. But largely it was the brains and skills of the talented Marcus Walker and his cross-disciplinary collaboration with the brilliant Jen Keane that made this all possible. 

Self-pigmenting textiles grown from cellulose-producing bacteria with engineered tyrosinase expression” by Walker et al., is published in Nature Biotechnology

https://doi.org/10.1038/s41587-024-02194-3