Scientists create enzyme 'cocktail' which digests plastic six times faster

A trans-Atlantic team of scientists has created a new enzyme 'cocktail' which is able to digest plastic up to six times faster than PETase, the enzyme the same team previously engineered in 2018.

The 'cocktail' consists of PETase, as well as a second enzyme, found in the same rubbish dwelling bacterium that lives on a diet of polyethylene terephthalate (PET), and can speed up the breakdown of plastic.

PET is the most common thermoplastic and is used in a range of products from single-use bottles to carpet to clothing. In the environment, PET takes hundreds of years to break down but PETase can shorten this time to a matter of a few days.

It works by breaking down PET into its building blocks, which allow for the infinite recycling of plastic and a drastic reduction in plastic waste and pollution, as well as the greenhouse gases that drive climate change.

The discovery of PETase brought with it the potential for a low-energy solution to tackling the problem of plastic waste and the prospect of a revolution in plastic recycling.

Now, the same team behind PETase has combined it with a 'partner' - a second enzyme called MHETase. Simply mixing the two together doubled the speed at which PET is broken down. By engineering a connection between the two to create a 'super-enzyme', the activity was sped up a further three times.

The team was co-led by the same two scientists who were at the helm of the PETase discovery - Professor John McGeehan, Director of the Centre for Enzyme Innovation (CEI) at the University of Portsmouth, and Dr Gregg Beckham, Senior Research Fellow at the National Renewable Energy Laboratory (NREL) in the US.

Professor McGeehan said: “Gregg and I were chatting about how 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.

“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.

“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.”

Professor McGeehan used the Diamond Light Source, a device that uses intense beams of X-rays 10 billion times brighter than the Sun to act as a microscope powerful enough to see individual atoms. This allowed the team to map out the 3D structure of the MHETase enzyme, giving them the molecular blueprints to begin engineering a faster enzyme system.

The researchers were then able to engineer the super-enzyme by "stitching" the DNA together into one long chain.

The technique is relatively common in the biofuels industry which uses it to break down cellulase, though McGeehan said that this is the first time to his knowledge that it is being used to break down plastic.

The problem of plastic pollution is one of the most pressing environmental issues facing the world. 

The full study is published in the journal Proceedings of the National Academy of Sciences of the United States of America. 

In 2016, a study by the World Economic Forum and the Ellen MacArthur Foundation found that if the projected growth in plastic consumption continues, by 2050 there will be more plastic in the oceans than fish.

In April, French company Carbios published a study into its own plastic-eating enzyme, which will be tested a demonstration plant near Lyon next year.

Other possible solutions include the tiny waxworm, which can eat through plastic, even polyethylene, a common and non-biodegradable plastic currently clogging up landfills and seas, thanks to its gut bacteria.

Mealworms, the larval stage of the mealworm beetle, could also play a part. Around 3,000-4,000 mealworms can break down one Styrofoam coffee cup in about a week thanks to the bacteria living in their gut.

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