Mutant enzyme that ‘eats’ plastic bottles could be a game-changer, scientists say

Scientists have created a mutant enzyme that digests plastic bottles. And this “inadvertent” discovery could result in a recycling solution for millions of tons of plastic polluting the world, according to researchers.

PET (polyethylene terephthalate), the plastic used in bottles, can take hundreds of years to break down in the environment, so it usually ends up as waste in landfills, littered on land or floating in oceans. The modified enzyme can break it down in just a few days, the study shows.

The discovery goes back to 2016 when a team of scientists from Britain’s University of Portsmouth and the U.S. Department of Energy’s National Renewable Energy Laboratory were studying the structure of a natural enzyme, called PETase, which is thought to have evolved in a waste recycling centre in Japan.

PETase has not existed in nature for very long, so the team wanted to see how the enzyme evolved and if it would be possible to improve it.

The goal was to only determine the enzyme’s structure, but the team went a step further and added some amino acids. They then inadvertently made PETase even better at breaking down plastic.

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“Serendipity often plays a significant role in fundamental scientific research and our discovery here is no exception,” John McGeehan, director of the Institute of Biological and Biomedical Sciences at the University of Portsmouth, said in a media release.

“Although the improvement is modest, this unanticipated discovery suggests that there is room to further improve these enzymes, moving us closer to a recycling solution for the ever-growing mountain of discarded plastics,” he said.

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The team, whose finding was published Monday in the Proceedings of the National Academy of Sciences journal, is now working on improving the enzyme further to see if they can make it capable of breaking down PET plastics on an industrial scale.

“It’s well within the 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 sustainably recycled,” McGeehan said.

How it works

The bacterial enzyme can break down plastic into its founding chemicals, the researchers said.

The team wanted to understand how it worked and used a super-powerful X-ray (10 billion times brighter than the sun) and made an ultra-high-resolution three-dimensional model of the enzyme.

Scientists then did a computer modelling, which showed PETase looked similar to another enzyme, cutinase, found in fungus and bacteria. The researchers hypothesized that PETase was a bit different than cutinase and has a part that allowed it to degrade plastic.

The scientists mutated the enzyme to make it more like cutinase and unexpectedly found that this enzyme was even better than the natural PETase at breaking down plastic.

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“We can all play a significant part in dealing with the plastic problem, but the scientific community who ultimately created these ‘wonder-materials,’ must now use all the technology at their disposal to develop real solutions,” McGeehan said.

— With files from Reuters and AFP