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Bacterium converts individual building blocks of nylon into value-added products

A team of scientists from the Institute of Bio- and Geosciences–Biotechnology at Forschungszentrum Jülich worked together with the company Novonesis to develop a bacterium that "eats" individual building blocks of different types of nylon and converts them into value-added products. The results of this research will help improve nylon recycling. The study has just been in the journal Nature Microbiology.

Synthetic polyamides, better known as nylon, have a long durability and high tensile strength. They are used in diverse industries and a variety of products—including tights, underwear and sportswear, as well as parachutes, nets, fishing lines, and components in the automotive industry.

Despite the wide range of possible applications and uses, the recycling rate for polyamides is currently less than 5%. Most nylon wastes are landfilled due to a lack of suitable recycling processes, discarded in the environment as fishing nets or ropes, or incinerated, which can release toxic substances.

Conventional recycling methods are often inadequate. Traditional mechanical recycling, where nylon is melted and reshaped into fibers or plastic products, is currently only done on a very small scale because it requires very pure nylon waste.

Alternatively, chemical recycling can break nylon material down into its building blocks, to reassemble into a new plastic, but the material is often not broken down fully. What remains instead is a mixture of individual molecules and short molecular chains—known as oligomers.

Compared to pure polymer building blocks, this mixture is difficult to process. And this is where the Jülich research team's innovation comes in.

Novel solution: Bacteria use nylon waste as a food source

The research team led by Prof. Dr. Nick Wierckx from the Institute of Bio- and Geosciences–Biotechnology at Forschungszentrum Jülich has genetically enhanced the versatile but harmless soil bacterium Pseudomonas putida, enabling it to metabolize this mixture of nylon building blocks and convert it into value-added products like biopolyesters.

The key to this breakthrough was a combination of genetic engineering and laboratory evolution, which makes it possible to efficiently teach bacteria new skills.

"Some bacteria develop the ability to recycle nylon building blocks more efficiently following random mutations in their genome. These cells have a growth advantage over others and can multiply faster. After a few generations in the laboratory, where nylon building blocks were the only source of nutrition, the bacterial culture eventually consists only of these specialized cells," says Wierckx.

By analyzing the genomes in detail, the researchers identified the responsible mutations and introduced them into Pseudomonas putida cells. In addition, genes for special enzymes, known as nylonases, were introduced to allow the bacteria to use short nylon chains from chemically decomposed nylon as an additional food source. The potential of such enzymes was already explored in an earlier study in collaboration with Novonesis.

The results are part of the recently completed European project Glaukos. Glaukos aimed to make the life cycle of clothing and fishing gear as well as their coatings more sustainable by creating new processes and bio-based textile fibers, while significantly reducing both the carbon footprint and plastic pollution.