A New Enzyme Found in Compost Just Set a Speed Record For Breaking Down Plastic


A plastic container put into a landfill can take hundreds of years to decompose naturally, but a newly discovered enzyme might consume the rubbish in under a day.

PHL7, a high-efficiency polyester hydrolase, was recently discovered nibbling on compost in a German graveyard.

Researchers discovered that it could degrade PET by 90% in 16 hours in the lab.

Although PHL7 is not the first natural 'plastic eater' discovered by scientists, it is the fastest.

A PET-eating enzyme known as LLC was discovered in a Japanese recycling factory in 2016. It's been hailed as a gold-standard plastic chomper in the years since. However, the recently discovered PHL7 is two times faster.

Scientists have been tweaking the LLC enzyme since 2016 to make an even more voracious mutant than the native one, but even this synthetic version can learn from PHL7.

"The enzyme discovered in Leipzig can make an important contribution to establishing alternative energy-saving plastic recycling processes," says microbiologist Wolfgang Zimmermann of Leipzig University in Germany.

"The biocatalyst now developed in Leipzig has been shown to be highly effective in the rapid decomposition of used PET food packaging and is suitable for use in an environmentally friendly recycling process in which new plastic can be produced from the decomposition products."

Unfortunately, neither PHL7 nor LCC are capable of thoroughly degrading PET plastics with higher crystallinity (a more structured molecular structure), such as those found in some bottles.

PHL7, on the other hand, can break down garbage in less than 24 hours if given a PET plastic fruit punnet.

Even better, the waste from this recycling process can be used to make new plastic containers.

Recycling has limitless possibilities. PET is manufactured in excess of 82 million metric tons each year, with just a small percentage being recycled into new plastic.

Even if a plastic product is taken to a recycling facility, the process of melting it down and creating something new is energy-intensive and costly.

Biological recycling, on the other hand, may be able to assist in the development of a low-cost, high-efficiency circular plastic economy. Scientists have been racing to produce plastic-eating microbes for this very purpose for the last few years.

PHL7 stands out among the possibilities that have been discovered thus far. It appears that a single building block in its DNA controls how quickly it degrades PET.

PHL7 has a leucine residue where other enzymes have phenylalanine residue at a specific point in its amino acid sequence. Leucine at this position has previously been associated with polymer-enzyme interaction.

The organism became significantly faster at breaking down plastic when researchers in Germany substituted phenylalanine with leucine in another enzyme. It was even more effective than PHL7.

In the lab, the PHL7 enzyme was also able to bind to more polymers than LLC enzymes.

"These results suggest that the phenylalanine/leucine replacement could be partially responsible for the changes in per-residue binding energy contributions in PHL7," the scientists write.

PHL7 is not only quick, but it also doesn't need any pre-treatment before it gets to work. Plastic will be eaten without being ground or melted.

The procedure of reassembling the byproducts does not require the use of petrochemicals.

"Thus," the authors conclude, "by employing powerful enzymes such as PHL7 it is possible to directly recycle post-consumer thermoform PET packaging in a closed-loop process with a low carbon footprint and without the use of petrochemicals, realizing a sustainable recycling process of an important PET plastic waste stream."

Given the global crisis of plastic pollution, that seems like a pipe dream. A prototype is now being developed by academics at Leipzig University.
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