Thermophilic bacterium achieves high conversion rate for plastic recycling

A research team has introduced an innovative solution for the depolymerization of polyethylene terephthalate (PET). This solution utilizes an engineered whole-cell biocatalyst based on the thermophilic bacterium Clostridium thermocellum.

Published in the Journal of Hazardous Materials, this study showcases an impressive 96.7% PET conversion rate, presenting a promising method for addressing plastic pollution and supporting a circular economy.

PET, a common fossil-based plastic, poses significant environmental challenges due to its persistence in landfills. Achieving circular utilization of PET is essential for reducing dependence on petroleum resources, lowering carbon emissions, and diminishing plastic waste.

While previous research has concentrated on developing PET-degrading enzymes, whole-cell biocatalysis has garnered attention for its advantages, including in situ enzyme production, simplified workflows, and high efficiency in large-scale plastic recycling.

This study builds on prior work published in Microbial Biotechnology, where the research team first demonstrated the concept of whole-cell catalytic PET depolymerization. In that study, the genetically engineered C. thermocellum expressed leaf compost cutinase (LCC) via a plasmid for high-temperature PET depolymerization.

In this study, the researchers integrated LCC directly into the chromosome of C. thermocellum, ensuring stable enzyme expression. They further enhanced the system by introducing LCC variants and co-expressing hydrophobic modules.

By optimizing reaction conditions and controlling pH, the researchers achieved a significant improvement in PET depolymerization efficiency with minimal accumulation of the intermediate product mono(2-hydroxyethyl) terephthalate (MHET).

When tested with pretreated PET bottle particles, about 97% of the added PET was converted into terephthalic acid (TPA), a key monomer used in producing new plastics or high-value chemicals. This high level of performance positions the system as a promising green solution for PET recycling.

Additionally, C. thermocellum is naturally capable of degrading cellulose, making it a potential candidate for directly processing mixed textile waste that contains cotton fibers and PET.

The research was a collaboration between Qingdao Institute of Bioenergy and Bioprocess Technology of the Chinese Academy of Sciences, Nanjing Tech University and Greifswald University.