- Scientists have created an enzyme which can digest some of the most commonly polluting plastics, providing a potential solution to one of the world’s biggest environmental problems.
- In 2016, it was discovered that a bacterium had naturally evolved to eat plastic at a waste dump in Japan.
- Researchers at University of Portsmouth and the Department of Energy’s National Renewable Energy Laboratory (NREL) in the US decoded the detailed crystal structure of the enzyme produced by the bug.
- The structure of the enzyme looked very similar to one evolved by many bacteria to break down cutin, a natural polymer used as a protective coating by plants.
- Researchers then tweaked the enzyme to see how it had evolved.
- Eventually they engineered a molecule in the laboratory that is even better at breaking down the PET (polyethylene terephthalate).
- The enzyme can also degrade polyethylene furandicarboxylate (PEF) a bio-based substitute for PET plastics that is being hailed as a replacement for glass beer bottles.
- The researchers are now working on improving the enzyme further to allow it to be used industrially to break down plastics in a fraction of the time.
- One possible improvement being explored is to transplant the mutant enzyme into an “extremophile bacteria” that can survive temperatures above 70C, at which point PET changes from a glassy to a viscous state, making it likely to degrade 10-100 times faster.
Bacteria that digests PET
- Japanese researchers had found that a bacterial species called Ideonella sakaiensis was responsible for PET degradation.
- The bacteria on adhering to PET surface secrete one enzyme onto the PET to generate chemical.
- That chemical is then taken up by the cell, where another enzyme breaks it down even further, providing the bacteria with carbon and energy to grow.
- Eventually the bacterium breaks down the entire PET chain.
What are PET plastics?
- PET – or polyethylene terephthalate – is the most common plastic used for soft drinks bottles and polyester fibers.
- PET plastics can persist for hundreds of years in the environment and currently pollute large areas of land and sea worldwide.
- Properties of PET include lightweight, shatterproof, easy to mould and colour and cheap to produce.
- The key raw material of PET is oil.
Recycling of PET
- PET bottles that are recycled have to be cleaned, sorted by colour, then shredded and dried to produce PET flakes.
- These can then be used to make new plastic but, due to impurities, it is not usually possible to make new, clear PET bottles.
- Instead, recycled bottles are mostly used to make polyester fibres.
- The recycling rates for PET bottles vary significantly around the world, from 31% in the US, to 48% in Europe, 72% in Japan and 90% in India.