A naturally occurring enzyme can now digest plastics.
PET, the strong plastic commonly used in bottles, takes hundreds of years to break down in the environment, but scientists have improved a way for the enzyme to digest these materials.
The modified enzyme, known as PETase, can start breaking down the material in just a few days.
This development could boost the recycling process, allowing plastics to be re-used more effectively.
Originally discovered in Japan, the enzyme is produced by a bacterium which “eats” PET.
Ideonella sakaiensis uses the plastic as its major energy source.
Researchers discovered n 2016 they had found the strain living in sediments at a bottle recycling site in the port city of Sakai.
“[PET] has only been around in vast quantities over the last 50 years, so it’s actually not a very long timescale for a bacteria to have evolved to eat something so man-made,” said Prof. John McGeehan, who was involved in the study.
Polyesters, the group of plastics that PET (also called polyethylene terephthalate) belongs to, do occur in nature.
“They protect plant leaves,” said McGeehan of the University of Portsmouth. “Bacteria have been evolving for millions of years to eat that.”
The switch to PET was nevertheless “quite unexpected” and an international team of scientists set out to determine how the PETase enzyme had evolved.
A high definition 3D model of the enzyme was created, using the powerful x-ray beamline at Diamond Light Source in Oxfordshire.
Once they understood its structure, the team noted they could improve the performance of PETase by adjusting a few residues on its surface.
To them it suggests the natural enzyme isn’t fully optimized yet and there is the potential to engineer it.
PETase was also tested on PEF plastic, a proposed plant-based alternative to PET that is similarly slow to degrade in nature.
“We were absolutely stunned when we did that experiment because it actually works better on PEF than PET,” McGeehan said.