Scientists engineered plastic-eating ‘super-enzymes’ that can break down bottles in days

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Used plastic bottles are seen at a waste collection point in Tokyo, Japan, November 21, 2018. Toru Hanai/Reuters
  • More than 300 million tons of plastic are produced annually worldwide, and most plastics take centuries to break down.
  • A new study describes a “super-enzyme” engineered using proteins derived from plastic-eating bacteria. It can recycle a common type of plastic in days.
  • Such enzymes could help address the growing problem of plastic pollution.
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More than 300 million tons of plastic are produced annually worldwide. Most take hundreds of years to break down, and even then, they just splinter into tiny microplastic pieces that will likely never biodegrade. Microplastics make it into the food we eat and show up in our poop.

But new types of engineered enzymes, created from plastic-eating bacteria, appear able to break down plastics in a matter of days.

These “super-enzymes” were made by researchers at the Centre for Enzyme Innovation in the UK and the National Renewable Energy Laboratory in Colorado. They break down a type of common plastic known as polyethylene terephthalate (PET) — used in single-use bottles as well as clothing and carpets — into its chemical building blocks.

Used at scale, they could reduce our reliance on fossil fuels (which are needed to produce new plastic), instead allowing manufacturers to reuse the same plastics over and over.

Engineering a ‘super’ plastic-eater

Plastic pollution scientist
John McGeehan, director of the Centre for Enzyme Innovation, is developing a ‘super-enzyme’ that can break down plastic. University of Portsmouth/Stefan Ventur/PA

Researchers first discovered plastic-eating bacteria in 2016 at a bottle-recycling facility in Japan. The organisms produce two enzymes that help them break down PET within weeks. Scientists dubbed the enzymes PETase and MHETase.

In 2018, a group at the Centre for Enzyme Innovation took PETase and tweaked it to increase the speed with which it deconstructed PET. This week, the team revealed in a new study that they improved on the process even further by stitching together DNA from PETase and MHETase into one “super-enzyme.”

“PETase attacks the surface of the plastics and MHETase chops things up further, so it seemed natural to see if we could use them together, mimicking what happens in nature,” biologist John McGeehan, the lead author of the study, said in a press release.

Whereas pitting PETase and MHETase against the same plastic doubled the breakdown speed they saw in 2018, this new creation breaks plastic down six times faster.

“We decided to try to physically link them, like two Pac-men joined by a piece of string,” McGeehan said.

Millions of tons of plastic enters the ocean each year

A Palestinian worker carries plastic items collected to be recycled in a factory in the northern Gaza Strip July 13, 2020.  REUTERS/Mohammed Salem
A Palestinian worker carries plastic items to be recycled in a factory in the Gaza Strip, July 13, 2020. Mohammed Salem/Reuters

Global production of plastics has increased rapidly over the last 70 years, and it continues to grow at around 8% per year. Up to 14 million tons of plastic enters the ocean annually, an estimated 40% of which is single-use products like plastic bottles, which wind up in the ocean within the same year they’re produced.

Scientists found more than 414 million pieces of plastic trash on scarcely populated islands in the Indian Ocean last year. Researchers have also discovered plastic in the guts of tiny creatures on the bottom of the Pacific Ocean, 36,000 feet down. One study showed more PET microplastics accumulate in the deep ocean than float on the surface.

Microplastic SouthIsland
Microplastics less than half a centimeter in size in the Cocos Islands. Jennifer Lavers

Addressing this plastic pollution problem, of course, requires limiting production. But innovations like the new super-enzymes can help recycle plastic that already exists.

The French company Carbios is also working to develop plastic-eating enzymes, aiming to utilise them in “industrial-scale recycling within five years,” according to The Guardian.

“If we can make better, faster enzymes by linking them together and provide them to companies like Carbios, and work in partnership, we could start doing this within the next year or two,” McGeehan told The Guardian.

Another option, though still in its infancy, is to use magnetic “nano-coils” to break down plastics.

Nanocoil
A nano-coil barely wider than one billionth of a metre. J. Kang et al./Matter July 31, 2019

A study published last year showed that these coils, which are just half the width of a human hair, create chemical reactions that convert plastic into carbon dioxide and water.