Plastic is an inescapable element of everyday life. It is virtually impossible to find an area on earth where there is no plastic lying around: whether it’s the pristine mountain areas in the Pyrenees or deep troughs in the ocean or uninhabited islands, plastic is everywhere.
And once dumped plastic also lingers in nature for a long time, because plastic – very often made for only single use – is poorly degradable. Often it takes decades or more for a plastic product to decay.
However, scientists at the University of Portsmouth are not going to let it go that easily. They have recently unveiled a cocktail of enzymes that can break down plastic at an accelerated rate and thus make an important contribution to the fight against plastic pollution.
The researchers focused in their study on polyethylene termphthalate (PET for short), a commonly used plastic that you probably have come in contact with from the so-called pet bottles. In nature, it can take centuries for PET to be completely degraded. But a few years ago, researchers announced that they had managed to lay their hands on an enzyme that can break down PET in a matter of days. During research into the structure of the enzyme – called PETase – the researchers accidentally adapted the `nzyme to the point where the plastic could break down another 20 percent faster. And now the scientists have gone one step further. They have combined PETase with another enzyme. The result is a ‘super enzyme’ that can break down plastic six times faster than PETase alone.
The super-enzyme consists of the enzyme MHETase in addition to PETase. The latter enzyme – like PETase – comes from bacteria found by the researchers on plastic waste. Where PETase ‘attacks’ the surface of plastics, MHETase focuses on breaking the plastic further into pieces. “It actually seemed very natural for us to use them together and, as it were, to mimic whatever happens in nature,” says researcher John McGeehan, from the University of Portsmouth.
The researchers combined the two enzymes and found that mixing them led to PET being broken down up to twice as fast. “We decided to try to physically attach them to each other,” says McGeehan, who worked with a researcher at the U.S. National Renewable Energy Laboratory (NREL). And once riveted together, the enzymes are able to break down PET three times faster.
It’s good news. Because although the discovery of PETase made researchers dream of a world free of plastic waste a few years ago, the rate at which the enzyme digested plastic was too low to make it a commercially attractive process within which the many pet bottles dumped worldwide could be broken down. Now that researchers have found a way to speed up the process, the approach seems to be becoming a lot more attractive.
An additional advantage of the combination of PETase and MHETase is that they break down PET in such a way that the original building blocks are ultimately left over. And it is quite easy – and without the need for fossil fuels, such as oil – to be made into new plastics.
