A gross fact of life is that we’re all ingesting plastic. Turtles eat plastic. Birds eat plastic. And one study found that humans eat a credit card worth of plastic each week. Now, scientists have engineered enzymes to eat plastic, too — but that may actually be a good thing.
In a study published in the Proceedings of the National Academy of Sciences on Monday, scientists found further evidence that the bacterium Ideonella sakaiensis produces two enzymes that break plastic down. Specifically, they work on polyethylene terephthalate, or PET, a type of plastic that’s used to make soda bottles and synthetic fabric for clothing.
A team of Japanese scientists first discovered the bizarre bacteria in 2016 while examining plastic items found in wastewater samples. Since then, scientists have been working diligently to re-engineer that bacteria’s enzymes. The new study presents a major breakthrough.
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The first enzyme the bacteria produces, PETase, can eat through solid plastic surfaces. PET is a polymer, meaning it’s a chemical compound made up of a bunch of molecules all strung together to form a complex, strong, durable structure. But when PETase gets onto the material, it breaks it down into simpler structures, including terephthalate (or TPA), bis(2-hydroxyethyl) TPA (or BHET), and mono-(2-hydroxyethyl) terephthalate acid (or MHET). Essentially, this speeds up the natural disintegration so that it takes days instead of centuries to breakdown plastic.
In 2018, the authors of the research engineered a version of the PETase enzyme, but it was only 20% more effective at degrading plastic than natural processes. But now, the researchers have tackled the second piece of the puzzle.
The scientists have created the second enzyme that the bacteria produces, which is called MHETase. Essentially, the researchers explain, MHETase breaks down MHET, created in the first step of the breakdown process, into even simpler forms: TPA and ethylene glycol. At this point, the substances left can easily be broken down further by other micro-organisms.
The researchers examined how these two enzymes reacted with pieces of plastic film in a lab setting, and found that without PETase around, MHETase doesn’t have any effect on the material. But the way the two work in concert could have big implications for the future of plastic waste if it’s able to scale.
The study found this two-enzyme “cocktail” can break down plastic at a rate six times faster than naturally-occurring processes. This could revolutionise the way the world disposes of plastic waste. PET is the most common form of plastic in the world, and the world generates millions of tons of plastic waste each year.
But tackling waste is just one aspect of the plastic crisis that needs solving. The process of creating the material, which is made from petrochemicals, is extremely polluting and climate-warming. So these new, exciting enzymes could play a role in reducing global pollution, but they’re not a panacea. Studies show we need a more holistic approach, including not making so much plastic in the first place.