Korean researchers tap into microbes for eco-friendly substitute to PET packaging 

A research team at the Korea Advanced Institute of Science and Technology (KAIST) has recently developed a microbial strain capable of producing a pseudoaromatic polyester monomer to replace PET in packaging using systems metabolic engineering.

The study, published in the Proceedings of the National Academy of Sciences, highlights the production of pseudoaromatic dicarboxylic acids that possess better physical properties and enhanced biodegradability compared to PET. These monomers, when synthesized as polymers, have the potential to address long-standing concerns over plastic pollution as eco-friendly substitutes.

Professor Sang Yup Lee from the Department of Chemical and Biomolecular Engineering at KAIST tells Packaging Insights: “We have previously developed microbial cell factories for the efficient production of succinic acid, glutaric acid, putrescine, cadaverine, butyrolactam, valerolactam, caprolactam and many others. These monomers produced from renewable resources rather than from fossil fuel will contribute to environmentally sustainable packaging.”

Eco-friendly chemicals

Previously, the chemical synthesis of pseudoaromatic dicarboxylic acids had been marred by issues such as low yield, poor selectivity, complex reaction conditions and the generation of harmful wastes.

The PET recycling process involves removing labels, shredding the plastic, washing, and using the recyclate as raw material for manufacturing.The KAIST team overcame these challenges by using metabolic engineering techniques to introduce Corynebacterium glutamicum, a bacterium well-regarded for amino acid production. The study builds a platform microbial strain that enhances the metabolic flow of protocatechuic acid, which is used as a precursor for several pseudoaromatic dicarboxylic acids and prevents the loss of precursors.

The team succeeded in producing five different types of pseudoaromatic dicarboxylic acids, including 2-pyrone-4,6-dicarboxylic acid (PDC) and four pyridinedicarboxylic acids (PDCA). The study reported the world’s highest production concentrations for 2,4-, 2,5-, and 2,6-PDCA, with 2,4- and 2,5-PDCA achieving titers on a gram-per-liter scale — a leap from previous milligram-scale outputs.

“PDC and PDCA are produced by metabolically engineered bacteria from renewable resources rather than from fossil fuel and can substitute terephthalic acid, a monomer in PET,” explains Lee.

“The significance lies in the fact that we have developed an eco-friendly technology that efficiently produces similar aromatic polyester monomers based on microorganisms.”

Potential industry shift

Global PET imports have drastically increased in recent years, with major exporters from Asia, including India, China and Turkey, contributing significantly in volume and value.

The research development is expected to be applied to various industrial processes for producing polyester.

“This study will help the microorganism-based bio-monomer industry replace the petrochemical-based chemical industry in the future,” says Lee.

However, he notes that the economic feasibility is still limited except for some of the monomers, including succinic acid and 1,4-butanediol, which are quite competitively produced by microbial cell factories.

“Further metabolic engineering together with bioprocess development are needed to make large-scale production competitive and support economic feasibility,” concludes Lee.