Enzymes that quickly break down plastic bags have been discovered in the saliva of waxworms, moth larvae that infest beehives.
The enzymes are the first reported to break down polyethylene within hours at room temperature and could lead to inexpensive ways to recycle the plastic.
The discovery came after a scientist, an amateur beekeeper, was cleaning an infested beehive and found the larvae were starting to eat holes in a plastic garbage bag. The researchers said the study showed that insect saliva “could be a repository for degradative enzymes that could revolutionize it.” [the cleanup of polluting waste]“.
Polyethylene accounts for 30% of all plastic production and is used in bags and other packaging, which accounts for a significant portion of the world’s plastic pollution. The only large scale recycling today uses mechanical processes and creates lower value products.
Chemical degradation could produce valuable chemicals or new plastic with further processing, avoiding the need for virgin plastic made from petroleum. The enzymes are easy to synthesize and overcome a bottleneck in plastic degradation, the researchers said, which is the initial breaking of polymer chains. This usually requires a lot of heating, but the enzymes work at normal temperatures, in water, and at neutral pH.
“My hives were being plagued by waxworms, so I started cleaning them by putting the worms in a plastic bag,” said Dr. Federica Bertocchini from the Biological Research Center in Madrid. “After a while, I noticed a lot of holes and we realized that it wasn’t just from chewing, it was also [chemical breakdown]so that was the beginning of the story.”
In terms of commercial application, it’s still in its infancy, the researchers say. “We have to do a lot of research and thinking about how to develop this new strategy for dealing with plastic waste,” said Dr. Clemente Arias, also at the Spanish research center. Alongside large-scale recycling plants, the scientists say, it may one day be possible to have kits in homes to recycle plastic bags into useful products. Other scientists are currently studying beetles and butterfly larvae for their potential to eat plastic.
Previous discoveries of beneficial enzymes took place in microbes, with a 2021 study suggesting that bacteria in oceans and soils around the world are evolving to eat plastic. It found 30,000 different enzymes that could break down 10 different types of plastic.
A super enzyme that quickly breaks down plastic drink bottles, which are typically made from PET plastic, was unveiled in 2020, inspired by a bug found in a landfill in Japan that was accidentally tweaked to increase its potency. An enzyme that breaks down PET has also been made from bacteria in leaf compost, while another beetle from a landfill can eat polyurethane, a plastic that is widely but rarely recycled.
Millions of tons of plastic are discarded every year, and pollution permeates the planet, from the top of Mount Everest to the deepest oceans. Reducing the amount of plastic used is vital, as is proper collection and treatment of waste, and full recycling could reduce new plastic production.
The research, published in the journal Nature Communications, identified 200 proteins in the waxworm’s saliva and narrowed down the two that had the plastic-eating effect. “This study suggests that insect saliva might [be] a repository of degrading enzymes that could revolutionize the field of bioremediation,” the researchers said.
The most important stories of the planet. Get all the environmental news of the week – the good, the bad and the big ones
Data protection: Newsletters may contain information about charities, online advertisements and content sponsored by third parties. You can find more information in our data protection declaration. We use Google reCaptcha to protect our website and the Google Privacy Policy and Terms of Service apply.
Waxworm larvae live and grow in the combs of beehives and feed on beeswax, which may be why they evolved the enzymes. Another possibility is that the enzymes break down the toxic chemicals produced by plants as a defense, which are similar to some additives in plastics.
Prof Andy Pickford, director of the Center for Enzyme Innovation at the University of Portsmouth, UK, said the discovery of the enzymes in waxworm saliva is exciting. “The reaction takes place within a few hours at room temperature, suggesting that enzymatic degradation could be a way to utilize polyethylene waste.”
A separate study published Tuesday in the journal Chem shows that creating a mirror-image version of a plastic-degrading enzyme means it’s much more resistant to degradation itself, prolonging its effectiveness. But Pickford said, “The high cost of chemically synthesizing mirror-image enzymes is likely to far outweigh any modest benefit from an extended enzyme half-life.”