Clothes are often made of nylon
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A genetically modified bacterium can break down chemicals in nylon and turn them into useful products, which could one day help us recycle clothes and fishing nets.
Nylons, or aliphatic polyamides, are plastics that are widely used due to their high durability and tensile strength, but their recycling rate is below 5 per cent.
“Production is around 10 million tonnes per year, but at the moment there’s basically no recycling,” says Nick Wierckx at the Jülich Research Centre in Germany. “Even incineration is difficult because you get cyanides when you burn them. The vast majority ends up in landfill.”
Nylon can be dissolved in a strong acid solution, but the mix of chemicals generated isn’t valuable enough to make this commercially useful.
Now, Wierckx and his colleagues have used a combination of genetic engineering and laboratory evolution to create a strain of the bacterium Pseudomonas putida that can break down the various compounds that are produced once nylon has been dissolved and turn them into something useful.
The bacterium is already known for degrading oil-based materials and breaking down oil in spills. It is also showing promise at breaking down plastics.
Wierckz and his colleagues took a strain known as P. putida KT2440 and gave it genes to help it metabolise various chemicals in dissolved nylon. They then cultured bacteria in the lab on these chemicals again and again until they found a strain that thrived. The researchers continued to modify and culture it until they had bacteria that could use the compounds in nylon to create useful products, such as polyhydroxybutyrate – a biodegradable plastic that isn’t harmful to living tissues.
“The Pseudomonas consumes almost all the pre-treated plastic,” says Wierckx. “What we can measure is that about 80 to 90 per cent is being consumed, but I think that is an analytical limitation, and it’s actually consuming almost everything because we don’t see anything left there.”
But improvements are needed before this technique could be used commercially, says Wierckx. For example, the amount of useful product is still only about 7 per cent of the dry bacterial biomass at the end.
Improving that will require further modification of bacteria and adjusting the chemicals used to tweak what is fed to the microorganisms, he says. “It’s probably going to be 10, 20, 30 years until we see this happening.”
We don’t need to worry that the bacteria will one day dissolve our underwear, though, says Wierckx. “It’s not going to eat all the plastics in our clothing and cars. We need to pre-treat the plastic so it becomes digestible.”
This also means we can’t yet use the bacteria to clean up old fishing nets in oceans. But Wierckx hopes that having this recycling process will encourage the future collection of old nets, clothing and car engines, which contain heat-resistant plastics, so they can be recycled.
