Plastic-eating ‘Pac-men’: Researchers say enzyme cocktail could revolutionize recycling

September 29, 2020, 10:35 AM UTC
Heavy equipment operators displace rubbish piles at the Kawatuna Landfill, Palu, Central Sulawesi Province, Indonesia on August 24, 2020.
Heavy equipment operators displace rubbish piles at the Kawatuna Landfill, Palu, Central Sulawesi Province, Indonesia on August 24, 2020. The Ministry of Environment and Forestry of the Republic of Indonesia reminds that the threat of garbage accumulation in Indonesia has continued to increase from time to time and has now reached 67 , 8 million tons. The amount of waste is estimated to double and plastic waste to increase by 35 percent by 2050 if not treated immediately. (Photo by Basri Marzuki/NurPhoto via Getty Images)
Basri Marzuki—NurPhoto/Getty Images

A new “enzyme cocktail” could be happily munching plastic at recycling sites within a couple of years, according to British and American researchers.

The technique wouldn’t just help to deal with the problem of ever-increasing plastic waste—because it returns the plastic to its original building blocks, it could also improve the recycling process in ways that are currently impossible, reducing the need to make new plastic out of fossil fuels. But until now, the process seemed too slow for commercial viability.

Back in 2016, scientists discovered plastic-eating bacteria at a recycling plant in Japan. Two years later, researchers from the University of Portsmouth in England and the U.S. Department of Energy’s National Renewable Energy Laboratory were trying to model the “PETase” enzyme contained in the bacteria to understand it better—and they accidentally engineered a mutant version that was even more efficient at breaking down the polyethylene terephthalate (PET) plastic that is commonly used to make bottles.

Fast-forward another two years, and the researchers have made yet another discovery.

As detailed in a research paper published Monday, the mutant PETase can be combined with another enzyme called MHETase, found in the same trash-dwelling bacterium. It turns out that the simple mixing of the two enzymes doubles the speed of their plastic digestion. And if a connection is engineered between the two enzymes, the digestion is another three times faster.

In other words, this enzyme cocktail can digest plastic up to six times faster than the original mutant PETase (which was itself 20% faster than the natural PETase) can.

“Our first experiments showed that they did indeed work better together, so we decided to try to physically link them, like two Pac-men joined by a piece of string,” said University of Portsmouth professor John McGeehan in a statement. “It took a great deal of work on both sides of the Atlantic, but it was worth the effort. We were delighted to see that our new chimeric enzyme is up to three times faster than the naturally evolved separate enzymes, opening new avenues for further improvements.”

McGeehan told the Guardian that commercial use could start happening “within the next year or two” if the academics work in partnership with biorecycling firms such as France’s Carbios, which recently found an enzyme that quickly digests plastic bottles, but at high temperatures that the new super-enzyme does not require.

The professor also told the newspaper that it might be possible to combine plastic-eating enzymes with those that break down natural fibers, which would allow for the currently impractical recycling of mixed fabrics that include both polyester and cotton.

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