Researchers at the University of Leipzig have discovered an enzyme that breaks down PET in record time. It has been known for some time that some enzymes, so-called polyester-cleaving hydrolases, can also degrade PET. But until now, the degradation process took too long to be of interest for commercial use. The research team has now discovered a "candidate" with which, for example, PET packaging from the supermarket should be completely degradable in less than a day.
 

 

The Leipzig research team led by biochemist Christian Sonnendecker isolated the microbial enzyme PHL7 from plant compost. The scientists had sampled the compost in a Leipzig cemetery in search of suitable enzyme candidates. Enzymes occur in nature that are synthesised by bacteria, for example, to decompose plant parts. The researchers had therefore taken targeted samples of leaf compost. In this way, they found the blueprint of an enzyme that decomposed amorphous (transparent and colourless) PET material at record speed in laboratory experiments at low temperatures in an aqueous reaction system. Within 16 hours, PHL7 decomposed the PET by 90 percent, twice as fast as the enzyme LCC, which is considered particularly effective and was discovered in Japan in 2012. "Our enzyme is thus twice as active as the gold standard among polyester-cleaving hydrolases," explains study leader Sonnendecker. The scientists attribute this ability to the amino acid leucine, which - unlike the other polyester-splitting hydrolases – is contained in PHL7. Sonnendecker says the Leipzig team then used the PHL7 enzyme to develop other enzymes that are even more effective. PHL7 also completely degrades PET films, releasing 91 mg of terephthalic acid per hour and 22 mg of the enzyme. The researchers themselves were surprised by the speed of degradation. It is not only the speed of decomposition that makes the enzyme interesting for commercial use. The polyester hydrolase not only decomposes the PET plastic, but also breaks it down into its basic building blocks, terephthalic acid and ethylene glycol, from which new PET can be produced. The result is a material, the quality of which is comparable to that of virgin material produced by petrochemicals. The research team is now working on a new pre-treatment method that will expand the enzyme's range of applications. This is because, until now, PET degradation by enzymes only works for amorphous PET, which is used for fruit packaging, for example, but not for plastic bottles, which are made of stretch blow-moulded PET.
 
Sources:

• swr.de (Feb. 22, 2023)
• pressenza.com (April 2, 2023)
• uni-leipzig.de (May 22, 2022)
• Low Carbon Footprint Recycling of Post-Consumer PET Plastic with a Metagenomic Polyester Hydrolase, Dr. Christian Sonnendecker, Dr. Juliane Oeser, P. Konstantin Richter, Patrick Hille, Ziyue Zhao, Dr. Cornelius Fischer, Dr. Holger Lippold, Paula Blázquez-Sánchez, Felipe Engelberger, Prof. Dr. César A. Ramírez-Sarmiento, Thorsten Oeser, Yuliia Lihanova, Dr. Ronny Frank, Dr. Heinz-Georg Jahnke, Dr. Susan Billig, Prof. Dr. Bernd Abel, Prof. Dr. Norbert Sträter, Prof. Dr. Jörg Matysik, Prof. Dr. Wolfgang Zimmermann, June 15, 2021
• Photo: Swen Reihold