The researchers – based at the University of Portsmouth and the US Department of Energy’s National Renewable Energy Laboratory – began working with an enzyme, PETase, which is capable of digesting polyethylene terephthalate (PET).
PET is one of the world’s most used plastics, and is used extensively in textiles, plastic bottles and food packaging. Although it is recyclable, huge quantities of PET is left in the environment to degrade over centuries.
The researchers used the Diamond Light Source synchrotron – which uses beams of X-rays to observe atomic structures – in order to solve its crystal structure, and better understand how the enzyme works. They found that PETase has certain features which indicate that it may have involved in an environment containing PET; potentially a waste recycling centre in the decades since PET was patented in 1941.
In order to test their hypothesis, the Portsmouth researchers mutated the PETase, and found that they had inadvertently engineered a new enzyme which is even more effective at degrading Pet than the naturally occurring enzyme.
It is also capable of degrading polyethylene furandicarboxylate (PEF), which has been proposed as an environmentally friendly alternative for PET in food packaging and other applications.
“Serendipity often plays a significant role in fundamental scientific research and our discovery here is no exception,” said Professor John McGeehan, director of the institute of biological and biomedical sciences at Portsmouth.
“Although the improvement is modest, this unanticipated discovery suggests that there is room to further improve these enzymes, moving us closer to a recycling solution for the ever-growing mountain of discarded plastics.”
Now, the researchers are focusing their work on improving the mutated PETase further using protein engineering and evolution, such that it could be used on an industrial scale to begin to break down millions of tonnes of waste plastic.
According to the researchers, the discovery means that it is possible that in the future “we will see an industrially viable process to turn PET and potentially other substrates […] back into their original building blocks so that they can be sustainably recycled.”
“Few could have predicted that since plastics became popular in the 1960s huge plastic waste patches would be found floating in oceans, or washed up on once pristine beaches all over the world,” said McGeehan.
“We can all play a significant part in dealing with the plastic problem, but the scientific community who ultimately created these ‘wonder materials’ must now use all the technology at their disposal to develop real solutions.”
Over the past months, increased attention has been focused on the problem of plastic waste. Last year, it was reported that worldwide consumption of plastic bottles had topped one million every minute, and numerous studies have demonstrated that tiny pieces of plastic are making their way inside marine life, including a third of the fish caught and eaten in the UK.
In January, Prime Minister Theresa May announced that the government would work to eliminate all avoidable plastic waste by 2042, such as by spreading the 5p charge on plastic bag to all UK retailers and encouraging supermarket to introduce plastic-free aisles. In January, the government announced a ban on microbeads: pieces of plastic less than one millimetre size which are commonly used in toiletries.