Posted in | Pollution | Biomaterials

Caterpillars Could Provide Biodegradable Solution to Plastic Pollution

Close-up of wax worm next to biodegraded holes in a polyethylene plastic shopping bag from a UK supermarket as used in the experiment. Credit: The research team.

Recently, it was discovered that a common insect larva eating beeswax breaks down chemical bonds in the plastic, used for making packaging and shopping bags, at uniquely high speeds. According to scientists, this discovery could result in a biotechnological approach to the polyethylene waste that chokes landfills and oceans.

Scientists have discovered that a caterpillar commercially bred for fishing bait is capable of biodegrading polyethylene, which is considered to be one of the most used and toughest plastics, commonly found clogging up landfill sites in the form of plastic shopping bags.

The wax worm, the larvae of the common insect Galleria mellonella, or greater wax moth, is a scourge of beehives all over Europe. In the wild, the worms survive as parasites in bee colonies. Wax moths lay their eggs inside hives where the worms actually hatch and grow on beeswax, hence the name.

Federica Bertocchini, an amateur beekeeper and a member of the scientific team, came up with a discovery while she was removing the parasitic pests from the honeycombs in her hives. The worms were temporarily place in a typical plastic shopping bag that became riddled with holes.

Bertocchini, from the Institute of Biomedicine and Biotechnology of Cantabria (CSIC), Spain, teamed up with colleagues Paolo Bombelli and Christopher Howe at the University of Cambridge’s Department of Biochemistry to perform a timed experiment.

Almost a hundred wax worms were exposed to a plastic bag from a UK supermarket. After just 40 minutes, holes started to appear, and after 12 hours the researchers observed a reduction in plastic mass of 92 mg from the bag.

Scientists explain that the degradation rate is very fast when compared to other latest discoveries, such as bacteria reported in 2016 to biodegrade some plastics at a rate of just 0.13mg a day.

If a single enzyme is responsible for this chemical process, its reproduction on a large scale using biotechnological methods should be achievable. This discovery could be an important tool for helping to get rid of the polyethylene plastic waste accumulated in landfill sites and oceans.

Paolo Bombelli, Department of Biochemistry, University of Cambridge

Polyethylene is increasingly used in packaging, and accounts for 40% of total demand for plastic products all over Europe, where up to 38% of plastic is discarded in landfills.  Every single year, a trillion plastic bags are used by people all over the world.

Plastic is generally considered to be highly resistant to breaking down, and even when it does the tiny pieces choke up ecosystems without degrading. The environmental toll is thus a heavy one.

An answer can still be provided by nature. The beeswax on which wax worms grow comprises of a highly diverse mixture of lipid compounds: constructing block molecules of living cells, including oils, fats and some hormones.

Further investigation is needed for the molecular detail of wax biodegradation, however, according to the researchers it is likely that digesting beeswax and polyethylene involves breaking similar varieties of chemical bonds.

“Wax is a polymer, a sort of ‘natural plastic,’ and has a chemical structure not dissimilar to polyethylene,” said CSIC’s Bertocchini, the study’s lead author.

The researchers performed spectroscopic analysis in order to prove that chemical bonds in the plastic were breaking. The analysis explained how the worms transformed the polyethylene into ethylene glycol, representing un-bonded ‘monomer’ molecules.

The team mashed up some of the worms and smeared them on polyethylene bags, with similar results, to confirm that it was not just the chewing mechanism of the caterpillars degrading the plastic.

The caterpillars are not just eating the plastic without modifying its chemical make-up. We showed that the polymer chains in polyethylene plastic are actually broken by the wax worms. The caterpillar produces something that breaks the chemical bond, perhaps in its salivary glands or a symbiotic bacteria in its gut. The next steps for us will be to try and identify the molecular processes in this reaction and see if we can isolate the enzyme responsible.

Paolo Bombelli, Department of Biochemistry, University of Cambridge

As the molecular details of the process become recognized, the researchers highlight that it could be used to develop a biotechnological solution on an industrial scale for managing polyethylene waste.

“We are planning to implement this finding into a viable way to get rid of plastic waste, working towards a solution to save our oceans, rivers, and all the environment from the unavoidable consequences of plastic accumulation,” Bertocchini added.  

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