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Can an enzyme solve our plastics problem?

3 minutes and 25 seconds, Matt Barrie, 17th April 2018.

Researchers in the U.S.A. and U.K. have modified a plastic-eating enzyme to speed up its abilities to digest plastic which could revolutionise plastics recycling.

Could an enzyme like this solve our plastics problem?

The scientists from the U.K.’s University of Portsmouth and the US Department of Energy’s National Renewable Energy Laboratory “tweaked” the structure of the naturally occurring enzyme PETase. PETase, was discovered in the city of Sakai, Japan in 2016 when scientists found that it was produced by a bacterium, Ideonella sakaiensis to break down PET (polyethylene terephthalate), a material widely used in bottles, in just a few days.

The bacterium uses PET as its major energy source. “[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,” commented Professor John McGeehan, who co-led the recent research.

“We’ve made an improved version of the enzyme better than the natural one already,” said McGeehan “That’s really exciting because that means that there’s potential to optimize the enzyme even further.”

There’s hope that the engineered enzyme could help in the fight against pollution caused by plastics, which take hundreds of years to break down in the environment and currently pollute large areas of land and sea worldwide.

The team of scientists is now working on improving the enzyme further to understand if Ideonella sakaiensis is capable of breaking down plastics on an industrial scale. Their initial goal had been simply to understand the enzyme’s structure.

Could this soon be an image of the past?
“It’s well within the realms of possibility that in the coming years we will see an industrially viable process to turn PET, and potentially other [plastics], back into their original building blocks so that they can be much more efficiently recycled,” McGeehan said.

Polyesters, the group of plastics that PET belongs to, do occur in nature. “They protect plant leaves,” explained McGeehan, “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 that they could improve the performance of PETase by adjusting a few residues on its surface. This suggests that 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,” Professor McGeehan told BBC News.

Yet big challenges lie ahead in turning an ingenious discovery into a real-world application. The enzyme is a number of years away from being deployed on a widespread scale. It will need to degrade PET faster than its current time of a few days, scientists will need to develop a technique to produce the enzyme at a financially viable price and question marks remain over its power on an industrial scale. But this is an example of accelerated science. A type of bacteria evolved to live off plastic in the last few decades.

Polyesters, industrially produced from petroleum, are widely used in plastic bottles and clothing. Current recycling processes mean that polyester materials follow a downward quality spiral, losing some of their properties each time they’re recycled. Bottles become fleeces, then carpets, after which they often end up in landfill.

PETase reverses the manufacturing process, reducing polyesters to their building blocks, ready to be used again, good as new.

“They could be used to make more plastic and that would avoid using any more oil…Then basically we’d close the loop. We’d actually have proper recycling,” explained Professor McGeehan.
Professor McGeehan is hopeful that this marks the beginning of a shift in the management of plastics. “There is an urgent need to reduce the amount of plastic that ends up in landfill and the environment, and I think if we can adopt these technologies we actually have a potential solution in the future to doing that.”

The author thanks Mary Halton and David Shukman for their help in creating this piece.

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