Polyester amide (PEA) is a promising class of polymers containing ester and amide bonds, combining the excellent properties of both polyesters and polyamides: the superior thermal and mechanical properties of polyamides, and the biocompatibility and biodegradability of polyesters. PEA can be used in various industrial applications, such as biodegradable plastics, as well as biomedical applications, including drug delivery systems and tissue engineering. Currently, the synthesis of PEA is limited to chemical methods.

Recently, a team led by Academician Sang Yup Lee from the Korea Advanced Institute of Science and Technology produced a nylon-like tough plastic for the first time through genetic engineering of microorganisms. The related results were published in Nature Chemical Biology on March 17.

Globally, about 400 million tons of non-degradable petroleum-based plastic waste and microplastics are produced annually, threatening the survival of wildlife, as well as human health and the Earth's environment. "This work highlights the role of biology in addressing this crisis," said Colin Scott, the enzyme engineering director at Australia's Uluu company.

The corresponding author of the paper, biomolecular engineer Sang Yup Lee from the Korea Advanced Institute of Science and Technology, said: "Bacteria naturally produce polymers to store nutrients when resources are scarce, but it is challenging to use bacteria to make nylon-like plastics because there are no enzymes in nature that can produce such polymers."

To solve this problem, researchers modified enzyme-encoding genes in a series of bacterial species and inserted them as plasmids (a type of circular DNA) into E. coli, which is commonly used for proof-of-concept work. Then, these genes encoded several new natural enzymes capable of linking molecular chains to produce polymers. The final product is a bioplastic called poly(ester amide) (PEA), which is primarily composed of polyester with a small amount of nylon-like amide bonds.

"Nylon is a 100% polymer containing amide bonds, so there is still a long way to go for bacteria to correctly mimic this plastic," said Li Xiangye.

The tests show that the physical, thermal, and mechanical properties of this PEA are comparable to those of polyethylene, one of the most widely used commercial plastics.

However, Shinichi Taguchi, a bioproduction engineer at Kobe University in Japan, said that due to the low frequency of amino acids binding to polymers, this plastic is unlikely to be as strong as polyethylene. "Adding an amino acid to a polymer typically leads to chain termination, resulting in low molecular weight, underdeveloped polymers."

The research team used large bioreactors to achieve a PEA yield of about 54 grams per liter, indicating that production can be scaled up. However, there are still many obstacles to overcome before this laboratory research can be translated into an industrial process.

Due to their large volume, these PEA aggregates cannot pass through the cell wall, so it is necessary to crush E. coli to release them. In addition, before processing the product into films or particles, a purification process is required.

"Currently, our microbial route is more expensive than oil-based plastics." Li Xiangye said, with further optimization, "it is expected that the production cost will gradually decrease."

Related paper information: https://doi.org/10.1038/s41589-025-01842-2