Nature bites back: Scientists modify plastic-digesting enzyme

17 Apr 2018 --- The battle against plastic pollution has taken an unexpected turn as an international scientist team develops an enzyme which naturally digests PET as its main energy source. Originally discovered in 2016 in sediments at a bottle recycling site in the port city of Sakai, Japan, the team has successfully modified the enzyme – known as Ideonella Sakaiensis – to break-down PET bottles at an accelerated rate of just three days. The research team believes that the enzyme has great potential in the global fight against plastic pollution.

The international team, led by Professor John McGeehan of the University of Portsmouth, UK, tested the evolutionary process of the enzyme, inadvertently discovering that they had improved the capabilities of the enzyme in breaking down PET bottles. “What actually happened was that we improved the enzyme, which was a bit of a shock,” says John McGeehan. “It’s great and a real finding.”

“What we are hoping to do is use this enzyme to turn this plastic back into its original components, so we can literally recycle it back to plastic,” says McGeehan. “It means we won’t need to dig up any more oil and, fundamentally, it should reduce the amount of plastic in the environment.”

Plastic takes centuries to biodegrade without human intervention, but the new enzyme is capable of accelerating the process to just a few days. The research team believes there is potential to accelerate this process even more with further modification. They believe it could offer a viable long-term and large-scale solution to global plastic pollution by supporting a circular recycling model in which plastics are broken-down and reused at end-of-life.

“You are always up against the fact that oil is cheap, so virgin PET is cheap,” adds McGeehan. “It is so easy for manufacturers to generate more of that stuff, rather than even try to recycle. But I believe there is a public driver here: perception is changing so much that companies are starting to look at how they can properly recycle these.”

The research team used the Diamond Light Source, near Oxford, UK – a highly-sophisticated X-ray machine which creates light 10 times brighter than the sun – to view the precise structure of the enzyme. The structure was found to be very similar to that of the bacteria capable of breaking-down cutin, a natural polymer used as a protective coating by plants. During testing, the team unexpectedly improved the enzymes plastic-digesting abilities.

“It is a modest improvement – 20 percent better – but that is not the point,” says McGeehan. “It’s incredible because it tells us that the enzyme is not yet optimized. It gives us scope to use all the technology used in other enzyme development for years and years and make a super-fast enzyme.”

Encouragingly, industrial enzymes in washing powders and biofuel production have been made to work up to 1,000 times faster. McGeehan believes this could also be achieved with Ideonella Sakaiensis. The Portsmouth University team, and their collaborators, the US National Renewable Energy Laboratory in Colorado, have since filed for a patent.

“Other types of plastic could be broken down by bacteria currently evolving in the environment, McGeehan says: “People are now searching vigorously for those.”

The scientific community response has generally been positive. Oliver Jones, a chemist at RMIT University in Melbourne, Australia, says: “I think [the new research] is very exciting work, showing there is strong potential to use enzyme technology to help with society’s growing waste problem.”

“Enzymes are non-toxic, biodegradable and can be produced in large amounts by microorganisms,” he says. “There is still a way to go before you could recycle large amounts of plastic with enzymes, and reducing the amount of plastic produced in the first place might, perhaps, be preferable. [But] this is certainly a step in a positive direction.”

Professor Adisa Azapagic of the University of Manchester, UK, likewise agreed that the enzyme could prove useful, but stated concern that it could lead to other forms of pollution: “A full life-cycle assessment would be needed to ensure the technology does not solve one environmental problem – waste – at the expense of others, including additional greenhouse gas emissions.”

The landmark discovery comes at a time when plastic pollution is a wide-scale, international public debate. There have been clear and regular indications in recent months that government bodies are working towards the development of a circular plastics economy – a model which the modified enzyme could potentially help to establish. The model was popularized by the Ellen MacArthur Foundation and has since been officially integrated into the EU Plastics Strategy.

Meanwhile, The UK recently joined a growing list of European nations to introduce a deposit-return scheme on plastic and other material containers. UK Chancellor, Philip Hammond, also recently confirmed plans to launch a public tax consultation on single-use plastics.

According to Innova Market Insights data, 58 percent of globally launched food and beverage products are packaged in plastic, a 5 percent increase from 2013, while 96 percent of all newly launched water products in 2017 are packaged in PET bottles. And according to the Earth Institute at Columbia University, only 9.5 percent of plastic is recycled and there are already 165 million tons of plastic debris in our oceans.

By Joshua Poole