Sometimes, new products get invented by accident. Potato chips, for example. The microwave, the ink jet printer, and the implantable pacemaker are on the list. My personal favorite involves scientists searching for a powerful new adhesive that could be used to glue airplanes together. They failed miserably and created one of the weakest adhesives ever known — which was perfect for making Post It notes. Now scientists from the US Department of Energy’s National Renewable Energy Laboratory, the University of Portsmouth in the UK, and the University of South Florida have accidentally discovered an enzyme that feasts on polyethylene terephthalate (PET), returning it to its original components. PET makes up about 20% of all the plastic waste in the world.
Plastic Eating Bugs In Japan
The researchers began by examining a bacterium first discovered at a waste dump in Japan in 2016. The bacterium was able to break down some plastic waste, but how? The scientists discovered the tiny bug produced an enzyme that could break down PET. They used the Diamond Light Source located near Oxford to study the enzyme. The Diamond Light Source produces an X-ray beam that is 10 billion times brighter than the sun. It is so bright, it can reveal individual atoms.
According to The Guardian, “The structure of the enzyme looked very similar to one evolved by many bacteria to break down cutin, a natural polymer used as a protective coating by plants. But when the team manipulated the enzyme to explore this connection, they accidentally improved its ability to eat PET.” Professor John McGeehan of the University of Portsmouth says, “What actually turned out was we improved the enzyme, which was a bit of a shock. It’s great and a real finding.”
“We originally set out to determine how this enzyme evolved from breaking down cutin — the waxy substance on the surface of plants– with cutinase, to degrading synthetic PET with PETase,” says Greg Beckham of NREL. “We hoped to determine its structure to aid in protein engineering, but we ended up going a step further and accidentally engineered an enzyme with improved performance at breaking down these plastics. What we’ve learned is that PETase is not yet fully optimized to degrade PET—and now that we’ve shown this, it’s time to apply the tools of protein engineering and evolution to continue to improve it.”
Unlocking A Door
In practice, the modified enzyme is only 20% better at breaking down PET than the original, but that’s 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.” Other industrial enzymes have been made to work up to 1,000 times faster within a few years of their discovery.
“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.” Now that the door has been opened, enzymes that dissolve other forms of plastic may be found in the lab. The dream is that someday, the huge mounds of plastic waste found in the world’s oceans could be treated chemically from the air, rendering them harmless to the environment and aquatic animals.
The driver behind plastic pollution is that petroleum products are so inexpensive. “You are always up against the fact that oil is cheap, so virgin PET is cheap,” says 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.” Of course, oil is cheap only because the companies that produce it do not pay for the damage their products are responsible for.
“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,” says Oliver Jones, a chemist at RMIT University in Melbourne, Australia, and not part of the research team. “Enzymes are non-toxic, biodegradable, and can be produced in large amounts by microorganisms. 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.”
And then, there is the Law Of Unintended Consequences to consider. Professor Adisa Azapagic of the University of Manchester agrees that the new enzyme could be useful but adds, “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.”
Azapagic is right to be cautious. People who live in Australia know about unintended consequences, thanks to early settlers who introduced rabbits into the environment so they could hunt them for their amusement. Ask people in the American south how they feel about kudzu or folks in the midwest about zebra mussels in the Great Lakes. Still, anything that could help the world address the problem of plastic waste deserves more attention.