Nature fights back with plastic-eating bacteria
Scientists have discovered a microbe that has evolved to break down PET. Bill Condie reports.
Plastic waste is everywhere, littering the countryside and clogging our waterways. Riding the ocean currents, it reaches every corner of the planet, never really going away, but simply breaking down into smaller and smaller pieces with a devastating effect on wildlife and the environment.
But now there are signs that nature is fighting back, with a microbe evolving that can eat the stuff.
One of the most common varieties of plastic is polyethylene terephthalate – or PET – a favourite for bottles of all kinds including virtually all soft drinks and water. Around 60 million tonnes of it is produced every year.
Until now, because of PET’s resistance to degradation, there have been no real strategies available to scientists to develop a viable remediation or recycling strategy.
But scientists have identified a bacterium that can use PET as its major source of energy.
“Until recently, no organisms were known to be able to decompose it,” writes Uwe Bornscheuer of Germany's University of Greifswald, noting that the bonds of PET molecules are notoriously strong.
The microbe, Ideonella sakaiensis 201-F6, when grown on PET, produces two enzymes that convert PET into its two environmentally harmless monomers – terephthalic acid and ethylene glycol.
The team of researchers who discovered the bacterium are still baffled as to where it came from.
“Remarkably, these enzymes seem to be highly unique in their function, compared to the closest related known enzymes of other bacteria, raising questions of how these plastic-eating bacteria evolved,” they write in the journal, Science.
The process used the bacteria gives hope that we may one day come up with an industrial application that could recycle PET safely. But that won’t be easy.
Bottles are made with highly crystallised PET, a tough substance that took a long time for the bacteria to eat away.
“It’s difficult to break down highly crystallised PET,” said Kenji Miyamoto from Keio University, one of the authors of the study.
“Our research results are just the initiation for the application. We have to work on so many issues needed for various applications. It takes a long time.”
Industry also poured cold water on the idea, saying current industrial processes are unlikely to be usurped by the bacteria’s approach.
"PET is 100% recyclable," Mike Neal, the chairman of the Committee of PET Manufacturers in Europe, told the Guardian.
"I expect that a biodegradation system would require a similar engineering process to chemical depolymerisation and as such is unlikely to be economically viable."