Eating into landfills: Researchers make breakthrough discovery with plastic-degrading enzymes

22 Mar 2022 --- Scientists that helped pioneer plastic-degrading enzymes have made an “important next step” in developing nature-based solutions to the global plastics crisis.

Researchers from the University of Montana, US, and the University of Portsmouth, UK, together discovered an enzyme that has a “remarkable capacity” to break down terephthalate (TPA) – one of the chemical building blocks of PET plastic, which is used primarily to make single-use drinks bottles, clothing and carpets.

The research, published in The Proceedings of the National Academy of Sciences (PNAS), was co-led by Professor Jen DuBois and Professor John McGeehan, who in 2018 led the international team that engineered a natural enzyme that could break down PET plastic.

The enzymes they discovered (PETase and MHETase) break the PET polymer into the chemical building blocks ethylene glycol (EG) and TPA. This new research describes the next steps, specifically for managing TPA.

The enzymes discovered could help breakdown and recycle used PET bottles.“While EG is a chemical with many uses – it’s part of the antifreeze you put into your car, for example – TPA does not have many uses outside of PET, nor is it something that most bacteria can even digest,” says DuBois.

“However, the Portsmouth team revealed that an enzyme from PET-consuming bacteria recognizes TPA like a hand in a glove. Our group at MSU then demonstrated that this enzyme, called TPADO, breaks down TPA and pretty much only TPA, with amazing efficiency.”

Enzymatic advances
With more than 400 million metric tons of plastic waste produced each year, the overwhelming majority of which end up in landfills, the researchers say they hope this discovery will open the door to improve bacterial enzymes, such as TPADO. “This will help tackle the challenge of plastic pollution and develop biological systems that can convert waste plastic into valuable products,” they remark.

“The last few years have seen incredible advances in the engineering of enzymes to break down PET into its building blocks,” says professor McGeehan, the director of the University’s Centre for Enzyme Innovation.

“This work goes a stage further and looks at the first enzyme in a cascade that can deconstruct those building blocks into simpler molecules. These can then be utilized by bacteria to generate [environmentally] sustainable chemicals and materials, essentially making valuable products out of plastic waste.”

“Using powerful X-ray at the Diamond Light Source, we were able to generate a detailed 3D structure of the TPADO enzyme, revealing how it performs this crucial reaction. This provides researchers with a blueprint for engineering faster and more efficient versions of this complex enzyme.”

BOTTLE Consortium
The study was undertaken as part of the BOTTLE (Bio-Optimized Technologies to keep Thermoplastics out of Landfills and the Environment) Consortium, an international collaboration between the US and UK, bringing together researchers from across a wide range of scientific areas to tackle plastic recycling and upcycling.

Recently, the consortium began working with Amazon to develop new chemical recycling methods, which the company’s scientists believe could drastically eradicate plastic waste in the near future.

Swedish researchers also recently discovered that plastic-degrading enzymes naturally increase as marine pollution rises throughout the world, indicating the environment is adapting to its degradation.

By Louis Gore-Langton

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