Ewing Worms' saliva helps break down plastic

WASHINGTON: Two substances in the saliva of wax worms - moth larvae that eat wax made by bees to build honeycombs -- easily break down a common type of plastic, researchers said on Tuesday October 4 in a potential advance in the fight against plastic pollution.

The researchers said the two enzymes identified in the caterpillar saliva were found to rapidly and at room temperature degrade polyethylene, the world's most widely used plastic, a major contributor to an environmental crisis that extends from ocean trenches to mountaintops.

The researchers concluded in 2017 that wax worms were capable of degrading polyethylene, though at the time it was not clear how these small insects did it. The answer was enzymes - substances produced by living organisms that trigger biochemical reactions.

For plastic to degrade, oxygen must penetrate the polymer or plastic molecule in an important initial step called oxidation. The enzymes performed this step in a matter of hours without the need for pre-treatment, such as applying heat or radiation.

The study, published in Nature Communications, is changing the paradigm of plastic biodegradation, said molecular biologist Federica Bertocchini of the Spanish National Research Council CSIC.

Plastic is made of polymers designed to be hard to break down and contains additives that increase durability, meaning it can remain intact for years, decades or centuries.

Bertocchini said that the very same features that make plastic the unique and useful material it is are creating one of the most critical problems of this century.

Plastics stay in the environment for a long time. It eventually breaks down into small particles, making it the source of micro and nanoplastic particles. These plastic particles have been found everywhere, from Antarctica to rain and tap water, which do not only cause obvious environmental issues but are a growing problem for human health, Bertocchini said.

Polyethylene, which was first created in 1933, is inexpensive, durable and does not interact with food, making it useful for food packaging and grocery store bags, among other applications.

Wax worms are the larvae of wax moths, a species called Galleria mellonella. The caterpillars, considered pests by beekeepers, feed on beeswax, pollen and honey, occasionally eating bee larvae.

The idea would be to make the worms' saliva enzymes synthetically, which the researchers succeeded in doing to break down plastic waste. Bertocchini said the use of billions of wax worms to do the job has drawbacks, including carbon dioxide as they metabolise the polyethylene.

In our case, the enzymes oxidise plastics, breaking it into small molecules. The study co-author Clemente Fernandez Arias, an ecologist and mathematician at CSIC, said this suggests alternative scenarios to deal with plastic waste in which plastics can be degraded in controlled conditions, limiting or eventually eliminating the release of microplastics.

A foundation related to the German plastics engineering company R chling helped fund the research. Bertocchini is one of two leaders of a Madrid-based company called Plasticentropy that is working to commercialize the use of enzymes to break down plastic waste.

Biodegradation by biological means or biodegradation is a goal that was previously focused on microorganisms. A handful of microorganisms were found to break down plastic but only slowing down and requiring pre-treatment, complicating the practicality of harnessing it.

Over the past three decades, plastic consumption has soared worldwide, with hundreds of millions of tons of waste annually ending up as waste and less than 10 percent of that being recycled.

The United Nations approved a landmark agreement to create the world's first global plastic pollution treaty in March after talks in Nairobi, with the goal of having a legally binding deal by 2024.