Scientists have developed a new enzyme variant that can completely break down waste plastic in under 24 hours, raising hopes that biological processes could provide a route to addressing perhaps part of the world's mounting plastic crisis. Researchers at the University of Texas at Austin announced Thursday that they had used artificial intelligence to successfully engineer a type of enzyme, called a hydrolase, that can break down PET plastic into its component molecules. These materials can then be reformed into new products. "The possibilities are endless across industries to leverage this leading-edge recycling process," said Hal Alper, one of the lead researchers and a professor in the McKetta Department of Chemical Engineering at UT Austin. "Beyond the obvious waste management industry, this also provides corporations from every sector the opportunity to take a lead in recycling their products. Through these more sustainable enzyme approaches, we can begin to envision a true circular plastics economy."

Plastic waste build-up in the environment is an enormous ecological challenge. Indeed, 40% of plastic waste goes around collection systems and ends up residing in natural environments. Enzymes that break down PET, PET hydrolases, have been previously developed but suffer from practical limitations with slow reaction rates and specific pH and temperature ranges. Now, researchers have used a structure-based, machine learning algorithm to engineer a robust and active PET hydrolase. The enzyme, FAST-PETase (functional, active, stable, and tolerant PETase), can break down environment-throttling plastics that typically take centuries to degrade in just a matter of hours and days.

Plastic waste poses an ecological challenge1–3 and enzymatic degradation offers one, potentially green and scalable, route for polyesters waste recycling4. Poly(ethylene terephthalate) (PET) accounts for 12% of global solid waste5, and a circular carbon economy for PET is theoretically attainable through rapid enzymatic depolymerization followed by repolymerization or conversion/valorization into other products6–10. Application of PET hydrolases, however, has been hampered by their lack of robustness to pH and temperature ranges, slow reaction rates and inability to directly use untreated postconsumer plastics11. Here, we use a structure-based, machine learning algorithm to engineer a robust and active PET hydrolase. Our mutant and scaffold combination (FAST-PETase: functional, active, stable and tolerant PETase) contains five mutations compared to wild-type PETase (N233K/R224Q/S121E from prediction and D186H/R280A from scaffold) and shows superior PET-hydrolytic activity relative to both wild-type and engineered alternatives12 between 30 and 50 °C and a range of pH levels. We demonstrate that untreated, postconsumer-PET from 51 different thermoformed products can all be almost completely degraded by FAST-PETase in 1 week. FAST-PETase can also depolymerize untreated, amorphous portions of a commercial water bottle and an entire thermally pretreated water bottle at 50 ºC. Finally, we demonstrate a closed-loop PET recycling process by using FAST-PETase and resynthesizing PET from the recovered monomers. Collectively, our results demonstrate a viable route for enzymatic plastic recycling at the industrial scale. Untreated, postconsumer-PET from 51 different thermoformed products can all be almost completely degraded by FAST-PETase in 1 week and PET can be resynthesized from the recovered monomers, demonstrating recycling at the industrial scale.