Designer Microbes Make Painkillers from Plastic Waste

Almost every aspect of a human’s daily life today is entangled with fossil fuels. A plastic toothbrush, a synthetic garment, or even a simple painkiller—each of these items started out as crude oil. Manufacturing these products releases tons of carbon emissions into the Earth’s atmosphere, making the planet hotter and less sustainable with each passing year. But there might be a way to reduce reliance on fossils fuels without having to shut down entire industries.

For the past decade, Stephen Wallace, a synthetic biologist at the University of Edinburgh, has been working on engineering microbes to produce diverse chemicals from sustainable sources. He has created bacterial factories that pump out nylon precursors using paper waste and vanilla flavor compounds from discarded plastic.^1,2 Now, Wallace and his team have designed bacteria that convert plastic waste into the widely used analgesic paracetamol.³ Published in Nature Chemistry, the technique has a negligible carbon footprint and introduces a new potential use for recycled plastic.

56 million tons of plastic bottles are produced every year, out of which roughly 45 percent end up in landfills, polluting the surrounding ecosystems.⁴ To put this waste to better use, Wallace and his team relied on a synthetic chemical reaction called Lossen rearrangement. This process can convert molecules produced via recycling of polyethylene terephthalate (PET), a widely used form of plastic, into new usable compounds.

Lossen rearrangement typically requires harsh conditions like high temperatures and alkalinity. However, Wallace and his team observed that the process could also occur in the bacterium Escherichia coli under biologically relevant parameters. To test its efficiency in bacteria, the researchers designed the chemical reaction to produce para-aminobenzoic acid (PABA), a molecule essential for the cells’ growth. After coaxing E. coli deficient in PABA to perform Lossen rearrangement of recycled plastic, the researchers observed that addition of phosphates to the growth medium drove the reaction within biocompatible limits.

Next, Wallace and his team investigated if these designer bacteria could be used to manufacture compounds that are traditionally fossil fuel sinks—medicines. Industries use petroleum products to make drugs such as aspirin, paracetamol, antibiotics, and antipsychotics.⁵ But paracetamol can also be synthesized in cells from PABA by two microbial enzymes.⁶ So, Wallace and his team introduced the genes for these enzymes into PABA-deficient E. coli, fed them recycled plastic waste, and watched the magic happen. The cells converted 92 percent of recycled plastic molecules into paracetamol.

Though the team needs to further standardize the process before production can be scaled up, the conversion of plastic waste into an essential pain reliever demonstrates the untapped potential of combining synthetic and biological chemistry.