The level of plastic pollution today is worrying. Among other lines of research, scientists are trying to find ways to use plastic without causing as much long-term damage to the environment around us. In this sense, a group of researchers from the University of Texas at Austin (United States) has created an enzyme capable of breaking down polyethylene terephthalate (PET) even in 24 hours .
The enzyme, baptized with the name of FAST-PETase (functional, active, stable and tolerant PETase) greatly reduces the time it takes for PET to decompose, since this material, frequently used in the manufacture of textiles, water bottles and other beverage containers, it would even take centuries to degrade. The enzyme could even be used to clean places contaminated with plastics.
In the tests carried out, the products made with the polymer polyethylene terephthalate (PET) decompose in a week and, in some cases, in 24 hours. “The possibilities are endless across industries to take advantage of this state-of-the-art recycling process,” says Hal Alper, a chemical engineer and one of the people who carried out the research.
“Beyond the obvious waste management industry, this also offers companies in all sectors the opportunity to take the lead in recycling their products,” says Alper.
The team has developed the enzyme FAST-PETase from a natural PETase, which allows bacteria to degrade PET plastic, and modified it using machine learning to locate five mutations that would allow it to degrade plastic more quickly under different environmental conditions.
Once the enzyme variant did its job of cutting the plastic into its basic molecular units (depolymerization), the researchers showed that they could rejoin the plastic (repolymerization) using chemical processes to create new plastic products .
The FAST-PETase finding involved the study of 51 different post-consumer plastic containers, five different polyester fibers, and fabrics and water bottles made from PET. In tests carried out on all these products, the enzyme variant proved effective, even at temperatures below 50 degrees Celsius.
“When environmental cleaning applications are considered, an enzyme that can function in the environment at room temperature is needed,” says Alper. “This requirement is where our technology has a huge advantage going forward.”
PET is present in many consumer packages, from textiles to water and soft drink bottles. On its own, it is thought to make up around 12% of all global waste. Another discouraging fact is this: globally, less than 10% of plastics are recycled . The introduction of FAST-PETase could contribute to the latter. The researchers say it is relatively cheap, portable, and not too difficult to scale up to the industrial levels that would be needed.
Currently, the most common methods of disposing of plastic are to put it in a landfill, where it rots at a very slow rate, or to burn it, which costs a lot, consumes a lot of energy and fills the atmosphere with harmful gases. It is clear that different strategies are needed and this could be one of them.
“This work really shows the power of bringing different disciplines together, from synthetic biology to chemical engineering to artificial intelligence,” says biochemist Andrew Ellington, who has also been involved in the research.
How to know if a bottle is made with PET
If a bottle or other plastic container is made with PET, a triangle formed by three arrows will appear at its base, which is nothing more than a simplification of the international recycling symbol (Möbius triangle). Inside the triangle there is a number between 1 and 7, which follows the classification of the American identification system SPI (acronym for Society of Plastics Industry) and, under it, some letters that allow us to recognize at a glance which plastic each bottle is made.
Number 1 corresponds to PET (polyethylene terephthalate), number 3 to the well-known PVC (polyvinyl chloride) and number 5 to PP (polypropylene). 6 is the number assigned to PS or polystyrene. The lower the number, the easier it is to recycle. These codes facilitate the separation of the different plastics according to their chemical composition for recycling processes.
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Reference:
Lu, H., Diaz, D.J., Czarnecki, N.J. et al. Machine learning-aided engineering of hydrolases for PET depolymerization. Nature 604, 662–667 (2022). https://doi.org/10.1038/s41586-022-04599-z
