Enzymes that rapidly break down plastic bags have been discovered in the saliva of wax worms, which are moth larvae that infest beehives.
The enzymes are the first reported to break down polyethylene within hours at room temperature and could lead to cost-effective ways of recycling the plastic.
The discovery came after one scientist, an amateur beekeeper, cleaned out an infested hive and found the larvae started eating holes in a plastic refuse bag. The researchers said the study showed insect saliva may be “a depository of degrading enzymes which could revolutionise [the cleanup of polluting waste]”.
Polyethylene makes up 30% of all plastic production and is used in bags and other packaging that make up a significant part of worldwide plastic pollution. The only recycling at scale today uses mechanical processes and creates lower-value products.
Chemical breakdown could create valuable chemicals or, with some further processing, new plastic, thereby avoiding the need for new virgin plastic made from oil. The enzymes can be easily synthesised and overcome a bottleneck in plastic degradation, the researchers said, which is the initial breaking of the polymer chains. That usually requires a lot of heating, but the enzymes work at normal temperatures, in water and at neutral pH.
“My beehives were plagued with wax worms, so I started cleaning them, putting the worms in a plastic bag,” said Dr Federica Bertocchini, at the Biological Research Centre in Madrid. “After a while, I noticed lots of holes and we found it wasn’t only chewing, it was [chemical breakdown], so that was the beginning of the story.”
In terms of commercial application, it is early days, the researchers say. “We need to do a lot of research and think about how to develop this new strategy to deal with plastic waste,” said Dr Clemente Arias, also at the Spanish research centre. As well as large recycling plants, the scientists said it might one day be possible to have kits in homes to recycle plastic bags into useful products. Other scientists are currently investigating beetles and butterfly larvae for their plastic-eating potential.
Previous discoveries of useful enzymes have been in microbes, with a 2021 study indicating that bacteria in oceans and soils across the globe are evolving to eat plastic. It found 30,000 different enzymes that might degrade 10 different types of plastic.
A super-enzyme that quickly breaks down plastic drink bottles, usually made from PET plastic, was revealed in 2020, inspired by a bug found in a waste dump in Japan and accidentally tweaked to increase its potency. An enzyme that breaks down PET has also been produced from bacteria in leaf compost, while another bug from a waste dump can eat polyurethane, a plastic that is widely used but rarely recycled.
Millions of tonnes of plastic are dumped every year, and the pollution pervades the planet, from the summit of Mount Everest to the deepest oceans. Reducing the amount of plastic used is vital, as is the proper collection and treatment of waste, and full recycling could cut new plastic production.
The research, published in the journal Nature Communications, identified 200 proteins in the wax worm saliva and narrowed down the two that had the plastic-eating effect. “This study suggests insect saliva might [be] a depository of degrading enzymes which could revolutionise the bioremediation field,” the researchers said.
Wax worm larvae live and grow in the honeycombs of beehives and feed on beeswax, which may be why they have evolved the enzymes. Another possibility is the enzymes break down the toxic chemicals produced by plants as a defence and which are similar to some additives in plastics.
Prof Andy Pickford, the director of the Centre for Enzyme Innovation at the UK’s University of Portsmouth, said the discovery of the enzymes in wax worm saliva was exciting. “The reaction happens within a few hours at room temperature suggesting that enzymatic breakdown may be a route to making use of polyethylene waste.”
A separate study published on Tuesday in the journal Chem shows that creating a mirror-image version of a plastic-degrading enzyme means it is much more resistant to breaking down itself, prolonging its effectiveness. But Pickford said: “The high expense of chemically synthesising mirror-image enzymes is likely to far outweigh any modest benefit from an enhanced enzyme half-life.”
