New study shows wax worm saliva could be the key to breaking down plastics

Wax worms, which are moth larvae that infest beehives, have an impressive feature, a recent study suggests.

Published in Nature Communications on October 4, Dr. Federica Bertocchini's group at Centro de Investigaciones Biológicas Margarita Salas (CIB-CSIC) demonstrates that wax worm saliva contains enzymes capable of degrading plastics.

The discovery of these enzymes, which belong to the phenol oxidase family and can quickly ignite polyethylene, opens up a slew of new possibilities for treating or recycling plastic waste.

"For plastic to degrade, oxygen must penetrate the polymer (the plastic molecule). This is the first step in oxidation, which is usually a result of exposure to sunlight or high temperatures, and represents a bottleneck that slows down the degradation of plastics like polyethylene, one of the most resistant polymers," explains Bertocchini in the statement.

"That is why, under normal environmental conditions, plastic takes months or even years to degrade," she adds. These enzymes that have been now discovered are the first and only known enzymes capable of degrading polyethylene plastic by oxidizing and breaking down the polymer very rapidly (after just a few hours of exposure) without requiring pre-treatment and work at room temperature.

Two enzymes: Demetra and Ceres

The team examined the saliva with an electron microscope and found a high protein concentration from which they extracted and identified two enzymes — Demetra and Ceres, two proteins that are members of the phenol oxidase enzyme family.

Researchers discovered that the Demetra enzyme significantly affected polyethylene, producing observable markings (small craters) on the plastic's surface.

After the polyethylene is exposed to this enzyme, breakdown products are produced. The Ceres enzyme also oxidizes the polymer but does not leave any traces, indicating that the two enzymes affect polyethylene in distinct ways.

The mechanisms by which these enzymes degrade plastic are unknown, and more research combining insect biology and biotechnology is needed.

The Röchling Foundation (Germany) contributed to the study, which was conducted in collaboration with the CIB's Federica Bertocchini, Ernesto Arias, and Mara Montoya groups, as well as the Institut de Biologia Molecular de Barcelona, the University of Burgos, Sequentia Biotech SL, the University of Basilicata, and the University of Cantabria.

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Abstract:

Plastic degradation by biological systems with re-utilization of the by-products could be a future solution to the global threat of plastic waste accumulation. Here, we report that the saliva of Galleria mellonella larvae (wax worms) is capable of oxidizing and depolymerizing polyethylene (PE), one of the most produced and sturdy polyolefin-derived plastics. This effect is achieved after a few hours of exposure at room temperature under physiological conditions (neutral pH). The wax worm saliva can overcome the bottleneck step in PE biodegradation, namely the initial oxidation step. Within the saliva, we identify two enzymes belonging to the phenol oxidase family that can reproduce the same effect. To the best of our knowledge, these enzymes are the first animal enzymes with this capability, opening the way to potential solutions for plastic waste management through bio-recycling/up-cycling.