Scientists Improve Plastic Recycling Enzyme

Scientists investigating bacteria that can eat plastic have accidentally made the relevant enzyme even more effective. It could significantly improve the options for recycling plastic bottles.

Such bottles are commonly made of polyethylene terephthalate (PET) in which the bond between molecules is particularly strong. That’s a big benefit when the material is being used and a big drawback when it comes to waste.

Several projects have explored cases of nature adapting to be able to break down the material. Some early results involved fungi, though this would be practically challenging to adapt for large-scale use.

The most successful project involved Japanese researchers hunting through samples of plastic bottles found in the wild as pollution. They found bacteria that could almost completely break down some bottles inside six weeks.

An international team has since explored the enzyme produced by the bacteria. They manipulated the enzyme to try to figure out if and how it had evolved from the enzyme some bacteria uses to break down cutin, a plant coating.

While this wasn’t the aim, it turned out the manipulation improved the bottle-eating performance by 20 percent. Professor John McGeehan said it wasn’t so much this figure that was exciting, but rather that it showed the bacteria hadn’t yet perfected the enzyme, meaning there could be even more room for improvement.

In the long run, researchers hope to be able to develop a bug spray (as in a spray containing bugs) to apply to the huge plastic ‘islands’ that have formed in the oceans.

As an early target, the enzyme could be used on bottles sent for recycling. At the moment PET bottles are most commonly recycled into plastic fibers used for carpets and clothing. If the enzyme works as hoped on an industrial scale, it could mean breaking down the bonds between molecules but being left with a material that can be turned into new bottles.

One option being explored is to adapt the enzyme to work at high temperatures so that it could be used on molten PET, which should dramatically speed up the process.