This project investigated a biocatalytic approach to the environmentally friendly recycling of polyethylene terephthalate (PET). The aim was to use biotechnological processes to close material cycles and promote a sustainable plastics economy. PET is a widely used plastic whose durability contributes to significant disposal and environmental problems. Enzymatic depolymerization offers a sustainable alternative to conventional chemical recycling processes, as it enables the selective cleavage of PET into its starting monomers terephthalic acid and ethylene glycol under mild conditions, thus supporting its reintroduction into high-value product cycles.This project investigated a biocatalytic approach to the environmentally friendly recycling of polyethylene terephthalate (PET). The aim was to use biotechnological processes to close material cycles and promote a sustainable plastics economy. PET is a widely used plastic whose durability contributes to significant disposal and environmental problems. Enzymatic depolymerization offers a sustainable alternative to conventional chemical recycling processes, as it enables the selective cleavage of PET into its starting monomers terephthalic acid and ethylene glycol under mild conditions, thus supporting its reintroduction into high-value product cycles.Environmentally friendly and resource-efficient recycling processes for plastic materials are urgently needed in order to improve the ecological fingerprint of frequently used plastics and to counteract the increasing threat to the environment from accumulating macro and microplastics.

⛶

Key aspects of the work included analyzing the influence of substrate properties and reaction conditions on PET hydrolysis and optimizing biocatalytically active cutinases through protein engineering. An improved cutinase variant was developed that was characterized by increased depolymerization of various PET substrates. Another focus was on the efficient production of the enzyme in microbial host organisms and the development of immobilization strategies that enable repeated enzyme use. To this end, stimuli-responsive polymers were used to ensure high activity, substrate accessibility, and stability of the immobilized biocatalyst and to optimally integrate enzyme recovery into the depolymerization process.

This project was supported by the Alfred Kärcher-Förderstiftung.

Publications:

Fritzsche S (2025): Enzymatic Recovery of Polyester Monomers: Protein Engineering, Recombinant Production and Immobilisation of Cutinases. Dissertation.

Walla B, Dietrich AM, Brames E, Bischoff D, Fritzsche S, Castiglione K, Janowski R, Niessing D, Weuster-Botz D (2025): Application of a Rational Crystal Contact Engineering Strategy on a Poly(ethylene terephthalate)-Degrading Cutinase. Bioengineering 2025, 12, 561.

Fritzsche S, Popp M, Spälter L, Bonakdar N, Vogel N, Castiglione K (2025): Recycling the recyclers: strategies for the immobilisation of a PET-degrading cutinase. Bioprocess Biosyst Eng 48, 605–619 .

Fritzsche S, Hübner H, Oldiges M, Castiglione K (2024): Comparative evaluation of the extracellular production of a polyethylene terephthalate degrading cutinase by Corynebacterium glutamicum and leaky Escherichia coli in batch and fed-batch processes. Microb Cell Fact 23, 274 (2024).

Fritzsche S, Tischer F, Peukert W, Castiglione K (2023): You get what you screen for: a benchmark analysis of leaf branch compost cutinase variants for polyethylene terephthalate (PET) degradation. React Chem Eng, 8, 2156-2169.

Contact