Enzymes that rapidly break down plastic bags have been discovered in the saliva of waxworms, the larvae of moths that infest hives.
The enzymes were first reported to degrade polyethylene within hours at room temperature and could lead to cost-effective ways to recycle plastics.
The discovery was made after a scientist, an amateur beekeeper, cleaned out an infected hive and discovered that the larvae had started eating holes in a plastic garbage bag. The researchers said the study showed that insect saliva could be a “repository of degrading enzymes that could revolutionize [the cleanup of polluting waste]”.
Polyethylene makes up 30% of all plastic production and is used in bags and other packaging that accounts for a significant portion of the world’s plastic pollution. The only recycling on a large scale today uses mechanical processes and creates lower value products.
Chemical breakdown could create valuable chemicals or, with some further processing, new plastics, avoiding the need for new virgin plastics made from petroleum. The enzymes can be easily synthesized and overcome the bottleneck in plastic degradation, the researchers said, which is the initial breaking of the polymer chains. This usually requires a lot of heating, but the enzymes work at normal temperatures, in water and neutral pH.
“My hives were inundated with wax worms, so I started cleaning them, putting the worms in a plastic bag,” said Dr. Federica Bertocini from the Center for Biological Research in Madrid. “After a while, I noticed a lot of holes and we found out that it wasn’t just chewing, but [chemical breakdown]so that was the beginning of the story.”
As for commercial application, it’s early days, the researchers say. “We have 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 from the Spanish research centre. In addition to large-scale recycling facilities, scientists said it may 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 potential to eat plastic.
Previous discoveries of beneficial enzymes have been in microbes, and a 2021 study shows that bacteria in oceans and soils around the world are evolving to eat plastic. 30,000 different enzymes have been found that can break down 10 different types of plastic.
A super-enzyme that quickly breaks down plastic drink bottles, usually made of PET plastic, was discovered in 2020, inspired by a bug found in a waste dump in Japan and accidentally tweaked to increase its power. An enzyme that breaks down PET is also produced by bacteria in leaf compost, while another landfill bug can eat polyurethane, a widely used but rarely recycled plastic.
Millions of tons of plastic are thrown away 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 the proper collection and treatment of waste, and full recycling could reduce the production of new plastic.
The research, published in the journal Nature Communications, identified 200 proteins in waxworm saliva and narrowed down two that had the effect of eating plastic. “This study suggests that insect saliva might.” [be] a repository of degrading enzymes that could revolutionize the field of bioremediation,” the researchers said.
Waxworm larvae live and grow in the honeycomb and feed on beeswax, which is why they may have developed enzymes. Another possibility is that enzymes break down toxic chemicals produced by plants as a defense, similar to some additives in plastics.
Professor Andy Pickford, director of the Enzyme Innovation Center at the UK’s University of Portsmouth, said the discovery of the enzyme in waxworm saliva was exciting. “The reaction occurs within a few hours at room temperature, suggesting that enzymatic degradation may be a route for utilizing polyethylene waste.”
A separate study published Tuesday in the journal Chem shows that creating a mirror version of the enzyme that breaks down plastic means it is much more resistant to self-degradation, prolonging its effectiveness. But Pickford said: “The high cost of chemically synthesizing a mirror image enzyme is likely to far outweigh any modest benefit from an extended half-life of the enzyme.”