Discovery of a polyesterase from Deinococcus maricopensis and comparison to the benchmark LCCICCG suggests high potential for semi-crystalline post-consumer PET degradation.

Plastic pollution remains a significant environmental challenge, with conventional waste management strategies proving insufficient in addressing the problem. Enzymatic degradation has emerged as a promising alternative, with LCCICCG, an engineered metagenome-derived cutinase, being the most effective in degrading polyethylene terephthalate (PET), the most commonly produced and discarded polyester. However, more efficient PET-hydrolases are needed for the upscaling of a PET-waste biorefinery. In this regard, the study reports the characterization of a novel, phylogenetically distinct, thermophilic polyesterase from Deinococcus maricopensis (DmPETase) and its comparison to LCCICCG. DmPETase is capable of degrading various synthetic polymers, including PET, polyurethane, as well as four semi-crystalline aliphatic polyesters. DmPETase was found to be comparable to LCCICCG at 50 °C in degrading semi-crystalline sections of post-consumer PET bottles, but it appeared to be less sensitive to crystallinity degree increase. This property makes DmPETase a new template for protein engineering endeavors to create an efficient biocatalyst to be integrated into the bio-recycling process of PET waste, without the need for amorphization of the materials.

Rate Response of Poly(Ethylene Terephthalate)-Hydrolases to Substrate Crystallinity: Basis for Understanding the Lag Phase.

The rate response of poly(ethylene terephthalate) (PET)-hydrolases to increased substrate crystallinity (XC ) of PET manifests as a rate-lowering effect that varies significantly for different enzymes. Herein, we report the influence of XC on the product release rate of six thermostable PET-hydrolases. All enzyme reactions displayed a distinctive lag phase until measurable product formation occurred. The duration of the lag phase increased with XC . The recently discovered PET-hydrolase PHL7 worked efficiently on "amorphous" PET disks (XC ≈10 %), but this enzyme was extremely sensitive to increased XC , whereas the enzymes LCCICCG , LCC, and DuraPETase had higher tolerance to increases in XC and had activity on PET disks having XC of 24.4 %. Microscopy revealed that the XC -tolerant hydrolases generated smooth and more uniform substrate surface erosion than PHL7 during reaction. Structural and molecular dynamics analysis of the PET-hydrolyzing enzymes disclosed that surface electrostatics and enzyme flexibility may account for the observed differences.

Standardized method for controlled modification of poly (ethylene terephthalate) (PET) crystallinity for assaying PET degrading enzymes.

Poly(ethylene terephthalate) (PET) is a polyester plastic, which is widely used, notably as a material for single-use plastic bottles. Its accumulation in the environment now poses a global pollution threat. A number of enzymes are active on PET providing new options for industrial biorecycling of PET materials. The enzyme activity is strongly affected by the degree of PET crystallinity (XC), and the XC is therefore a relevant factor to consider in enzyme catalyzed PET recycling. Here, we present a new experimental methodology, based on systematic thermal annealing for controlled preparation of PET disks having different XC, to allow systematic quantitative evaluation of the efficiency of PET degrading enzymes at different degrees of PET substrate crystallinity. We discuss the theory of PET crystallinity and compare PET crystallinity data measured by differential scanning calorimetry and attenuated Fourier transform infrared spectroscopy.•This study introduces a simple method for controlling the crystallinity of PET samples via annealing in a heat block.•The present methodology is not limited to the analytical methods included in the methods details.