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Could this plastic-eating enzyme save our planet?

Imagine if we didn’t have to make new plastic anymore? Discovering the enzyme PETase could make it easier to recycle plastic multiple times over, helping to solve the problem of plastic waste in the environment.

At a bottle recycling plant in Japan, scientists discovered a bacteria whose main food source is plastic. This bacteria produces an enzyme that breaks PET plastic down into its basic building blocks. The enzyme can then be extracted from the bacteria to help improve our recycling process.

What are plastic bottles made of?

A microscopic image of the tiny fibres that make up PET plastic. Image (c) futurepics.com

Most plastic bottles are made of polyethylene terephthalate (PET for short). If you looked through a powerful enough microscope, you would see it is made up of millions of tiny plastic fibres. Inside these fibres are even smaller molecules which are the building blocks of PET.

The chemical structure for PET. Image (c) Wiki Commons

This is the chemical structure for one building block of PET. By joining lots of these together, you end up with a long chain. Hundreds of millions of chains joined together becomes one plastic fibre. And enough of these plastic fibres combined can be made into pellets, which are then melted and injected into plastic moulds.

What happens when a plastic bottle is recycled?

A close up image of crushed PET plastic flakes, to be used in the recycling process. Image (c) royalinterpack.com

When a used plastic bottle is taken to a recycling centre, it is crushed and shredded into small fragments. This releases little ‘flakes’ of PET. They are melted into pellets, melted again and finally injected into moulds to create ‘new’ bottles.

But because PET is so sensitive to heat, this recycling process can only be done a fixed number of times. The material eventually becomes too weak to be melted and recycled again.

How does this discovery change things?

Photograph of water bottles on the production line at a water bottle factory. Image (c) alexta/Shutterstock

Until now, researchers struggled to find a way to recycle PET plastic indefinitely. But after researching this plastic-munching bacteria, they discovered an enzyme called PETase that breaks down PET into basic building blocks – without any need for heat. This means that PET plastic can be made, broken down and remade without ever wearing out.

Questions to ask your class

  1. What small changes could you make to your life to reduce your use of plastic?
  2. The un-recyclable plastic waste we create now will be around for hundreds to thousands of years. This means future generations will have to deal with what we leave behind. Do you think this is fair? Who should pay the cost of dealing with this?
  3. In the past, many items were made to be reusable like nappies, pens, and milk bottles. What do you think was the drive behind shifting to single use products? Do you think there was more than one reason behind it?
  4. What properties does plastic have that have made it so widespread?