# Cellular Upcycling of Polyethylene Terephthalate (PET) With an Engineered Human Saliva Metagenomic PET Hydrolase

## TL;DR

Scientists engineered bacteria to break down PET plastic and convert it into useful chemicals at body temperature.

## Contribution

A two-strain Escherichia coli system (PETCAT) is developed for PET degradation and upcycling at moderate temperatures.

## Key findings

- MG8G127Y/F250A and MG8N125S/G127Y/F250A mutants show enhanced PET hydrolysis at 37°C.
- PETCAT system enables whole-cell PET valorization into catechol under physiological conditions.

## Abstract

Recent advances in biocatalytic recycling of polyethylene terephthalate (PET) using PET hydrolase enzymes have sparked interest in integrating PET degradation capabilities into living systems. Although cell‐based strategies are limited by the mesophilic temperature constraints of microbial hosts, they offer a unique opportunity to couple PET depolymerization with biological upcycling into value‐added chemicals. Here, a comprehensive approach for the cellular degradation and valorization of PET is reported. The crystal structure of MG8, a PET hydrolase identified from the human saliva metagenome is solved, and molecular dynamics simulations are used to pinpoint loop regions for targeted mutagenesis aimed at enhancing activity under moderate temperatures. Over 1000 MG8 loop variants are evaluated with a high‐throughput mass spectrometric screening platform. Two catalytically improved mutants—MG8G127Y/F250A and MG8N125S/G127Y/F250A—exhibit significantly enhanced PET hydrolysis at 37°C. To enable whole‐cell PET valorization, a two‐strain Escherichia coli system called PETCAT is constructed: one strain is engineered to secrete MG8G127Y/F250A for PET degradation, and the other harbors a synthetic pathway comprising seven heterologous genes for the conversion of terephthalic acid (TPA) into catechol, a versatile intermediate used in pharmaceuticals and fragrances. This study establishes a modular, one‐pot microbial platform for PET recycling and upcycling under physiologically relevant conditions.

To enable whole‐cell PET valorization, PETCAT is constructed as a two‐strain Escherichia coli system: one engineered to secrete the human saliva metagenomic PET hydrolase optimized for PET degradation at moderate temperatures; and another harboring a synthetic pathway for the conversion of terephthalic acid, a major PET monomer, into catechol—a versatile intermediate for pharmaceuticals and fragrances.© 2026 WILEY‐VCH GmbH