This enzyme is capable of devouring plastic!

More than 70% of the waste found on beaches today is plastic (food packaging, bottles, caps, bags, etc.). In France, as in other countries, a number of measures have been implemented (and others will come) to reduce the amount of plastic produced and consumed. The goal? Remove disposable plastic. But what about the billions of tons of waste accumulated so far?

Recycling procedures are limited to certain families of plastics, while incineration is an expensive and energy-intensive process that releases harmful gases. Enzymatic degradation seems to be a cheaper and more environmentally friendly solution, but it has also shown certain limitations. Using a machine learning algorithm, the researchers were able to circumvent these limitations and develop a more efficient enzyme.

A mutant enzyme created by machine learning

Poly (ethylene terephthalate) or PET accounts for 12% of the world’s solid waste. In fact, it is used in the composition of most food packaging (packets of cookies, bottles of water and soda, bags of salads, etc.) and certain fibers and textiles. For this particular plastic, a circular carbon economy can theoretically be achieved by rapid enzymatic depolymerization, followed by repolymerization or improvement in other products.

But PET hydrolases have so far shown limited efficacy: reaction rates are relatively slow and enzymes generally cannot directly attack plastic waste without prior treatment. In addition, they have been shown to be resistant to certain conditions of pH and temperature.

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Researchers at the Cockrell School of Engineering and the College of Natural Sciences at the University of Texas at Austin used a machine learning model to generate new mutations in a natural enzyme, PETase, which is able to degrade plastics made with this polymer. The model determined which mutations would allow enzymes to depolymerize post-consumer plastic waste more rapidly at low temperatures.

The resulting mutant enzyme, called FAST-PETase, has five mutations compared to wild-type PETase, which make it functional, active, stable, and resistant (hence the acronym FAST). The team was able to test its effectiveness in post-consumer untreated PET from 51 different thermoformed products, five different polyester fibers and fabrics and several bottles, all made of PET. The results, described in the review Naturethey are awesome.

Degradation tests of various PET containers for FAST-PETase enzymes. The 51 tested post-consumer products were eliminated in less than a week (it only took 24 hours in some cases). Credit: YouTube / UT Austin

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Efficient degradation even at low temperatures

The new enzyme has been shown to be able to carry out a complete circular process, consisting of breaking down the plastic into smaller fragments (depolymerization) and then reconstituting it chemically (repolymerization), all at temperatures between 30 and 50 °. C and over a wide pH range. In some cases, plastics have broken down into monomers in just 24 hours. ” Beyond the interiorobvious interest in thewaste management industry, also offers companies from all sectors the opportunity to take the initiative to recycle their products “Al Hal Alper, a professor of chemical engineering at UT Austin and co-author of the study presenting this new enzyme.

If not all plastics are recycled today, it is mainly because they have not been classified. In addition, some plastics are actually composed of complex mixtures or associated with other materials, which would require more sophisticated and expensive recycling procedures. Other alternative processes involve energy-intensive glycolysis, pyrolysis and / or methanolysis processes.

>> Read also: A new reaction to transform plastic bags into fuel

Currently, biological approaches are the solutions that consume the least energy possible to eliminate plastic waste. Thus, for more than a decade, scientists have been exploring the capabilities of enzymes to destroy plastic. But so far, its effectiveness at low temperatures has not been conclusive, making it difficult to take this approach on an industrial scale. ” With these more sustainable enzymatic approaches, we can begin to imagine a true circular economy of plastics. “says the scientist.

The team is now working to find a way to produce these enzymes on a large scale, for both industrial and environmental application. FAST-PETase could be used, for example, to clean up landfills, but researchers are also investigating various ways to bring enzymes directly into the field to clean up contaminated natural sites, which means they are just as effective at room temperature. . ” This is where our technology comes in handy for the future. said the Alper.

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