How do wax worms decompose plastic?

Animals that degrade plastic

It all started by chance when Bertocchini, a beekeeping enthusiast, noticed that her hives were affected by ‘Galleria mellonella’. In fact, this species that feeds on beeswax and honey is a real pest for beekeeping farms all over Europe (the moths lay their eggs inside the hives and the caterpillars grow in a beeswax environment). “I decided to remove the maggots and leave them in a plastic bag while I cleaned the hives. After getting everything ready, I went back to the room where they were and saw that they were everywhere, that they had escaped from the bag even though it was still closed. I found that the bag was full of holes. There was only one explanation: the caterpillars had made them and had escaped through there. That’s when the project began&rdquor, says the CSIC scientist.

Then, in collaboration with her colleagues Paolo Bombelli and Christopher Howe, from the University of Cambridge, in the United Kingdom, they decided to carry out a timed experiment. About a hundred ‘Galleria mellonella’ caterpillars were placed in a plastic bag, typical of supermarkets. “The holes started to appear just 40 minutes later and after 12 hours there was a clear reduction in the mass of plastic in the bag&rdquor, the authors write. The research will be published in the journal Current Biology.

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Wax worms eat the bees’ production.

To rule out the chewing process as a source of such degradation, the team applied a thick mixture of worms that had recently died to the plastic and waited. Indeed, they discovered that the liquid larvae could also bore holes in the plastic. This led Bertocchini and his colleagues to think that an enzyme in the worms or in the bacteria living in and on their bodies was responsible for dissolving the plastic.

That enzyme converted polyethylene into ethylene glycol, a chemical compound normally used in antifreeze.  Bertocchini hopes to identify the exact enzymes that break down polyethylene in future research.

In 2014, Wu and colleagues at Stanford University discovered that a gut bacterium from another species of wax worm could break down polyethylene, although it generated different byproducts. A 2016 study identified enzymes in one species of bacteria capable of breaking down a type of plastic called polyethylene terephthalate.

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Galleria mellonella

Recently, research results were published in the journal “Biology Letters” (http://rsbl.royalsocietypublishing.org/content/14/9/20180479) confirming that common mosquitoes (Culex pipiens), actually their larvae, eat plastic due to their feeding habits, considered as a vector or transmitting agent of plastic waste (microplastics) in the food chain of many other animals (e.g. insectivorous birds), which can lead to negative consequences to the environment.

However, there are studies that indicate that there are various organisms such as bacteria, fungi and worms that, in addition to eating plastic, degrade it. The mealworm (Tenebrio molitor) can feed on polystyrene foam (a non-biodegradable plastic) transforming 50% of it into carbon dioxide and the other 50% into biodegraded excrement. These worms degrade plastic due to bacteria in their digestive tract (https://pubs.acs.org/doi/10.1021/acs.est.8b02301). Currently, this kind of polyethylene plastics are burned or degraded with environmentally aggressive chemical processes.

Tenebrio molitor as biodegradation of polystyrene

Federica Bertocchini, a researcher at the Institute of Biomedicine and Biotechnology of Cantabria, discovered this particularity by chance and thanks to her hobby of beekeeping. So, seeing one day that her honeycombs were full of worms, she decided to remove them and put them in a plastic bag from which, shortly after, the insects had escaped. “I noticed that the bag was full of holes. There was only one explanation: the worms had made them and escaped through there. That’s when this project began.

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