Enzymes as recycling heroes: Researches sustainable plastic recycling

The enzyme PHL7, first described in 2021 by Sonnendecker after being isolated from a compost sample from Leipzig’s Südfriedhof cemetery, is considered one of the few naturally occurring hyperactive PET-degrading enzymes. Until now, however, it had been too unstable and insufficiently active for technical applications – particularly under real industrial conditions. The new study overcomes these obstacles: “Using bioinformatics predictions, we introduced targeted mutations into the amino acid sequence, resulting in significantly improved variants. These variants exhibit greater stability, higher activity and reduced dependence on salt concentrations – a decisive advantage, as the enzyme can now also function in ordinary tap water,” explains Künze. 

For the experimental work carried out between summer 2022 and mid-2025, the research group led by Künze and Sonnendecker employed a wide range of modern methods: X-ray crystallography revealed the three-dimensional structure, impedance spectroscopy provided real-time data on the progress of the reaction, and molecular dynamics simulations helped decipher the enzymatic degradation process at molecular level. The enzyme variants were tested in bioreactors under conditions closely resembling those used in industry – with promising results. The findings have already formed the basis of a patent application.

“The PHL7 variants we have developed are now genuine candidates for industrial application,” says Sonnendecker. ESTER-Biotech, a start-up founded in Leipzig in 2025 as a spin-off from Leipzig University, is already planning to transfer the technology to a pilot plant. In the long term, enzymatic recycling could help make the plastics economy more circular and sustainable. The project is not yet complete: further optimisation using artificial intelligence is planned, along with the development of enzymes for other biodegradable plastics such as PLA and PBS. Whether the technology proves commercially viable will become clear over the coming years and will depend not only on technical advances, but also on economic factors.

More than 20 years ago, Professor Wolfgang Zimmermann at Leipzig University was already conducting pioneering research into plastic-degrading enzymes, with the aim of recycling plastics such as PET under environmentally friendly conditions. The current study brings the field one step closer to achieving that goal.