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The Very Hungry Caterpillar

05 May 2017 | Updated 01 January 1970
 

A caterpillar (that is often used in fishing bait) has been found that will degrade shopping bags - suggesting there is a biodegradable solution to plastic pollution.

A common insect larva (Galleria Mellonella or the wax worm) that eats beeswax has been found to break down chemical bonds in the plastic used for packaging and shopping bags at uniquely high speeds. Scientists say the discovery could lead to a biotechnological approach to the polyethylene waste that chokes oceans and landfills.

The caterpillar produces something that breaks the chemical bond, perhaps in its salivary glands or a symbiotic bacteria in its gut Cambridge University researchers are surmising as they conduct further tests and trials. They have already released one educational paper. The hope is that rather than introduce hungry caterpillars to waste sites, scientists can re-create the suspected enzyme and reproduce it in  much larger quantities.

The discovery came when a bee keeper found the parasite in one of her hives and removed them to a plastic bag which the caterpillars promptly munched through. Fortunately, the bee keeper in question was from the Spanish National Research Council with colleagues at the University of Cambridge’s Department of Biochemistry.

 

Experiment

Around a hundred wax worms were exposed to a plastic bag from a UK supermarket. Holes started to appear after just 40 minutes, and after 12 hours there was a reduction in plastic mass of 92mg from the bag.

Scientists say that the degradation rate is extremely fast compared to other recent discoveries, such as bacteria reported last year to biodegrade some plastics at a rate of just 0.13mg a day. Polyethylene takes between 100 and 400 years to degrade in landfill sites.

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

Polyethylene is largely used in packaging and accounts for 40% of total demand for plastic products across Europe – where up to 38% of plastic is discarded in landfills. People around the world use around a trillion plastic bags every single year.

Generally speaking, plastic is highly resistant to breaking down and even when it does the smaller pieces choke up ecosystems without degrading. The environmental toll is a heavy one.

The beeswax on which wax worms grow is composed of a highly diverse mixture of lipid compounds: building block molecules of living cells, including fats, oils and some hormones.

The researchers say it is likely that digesting beeswax and polyethylene involves breaking similar types of chemical bonds, although they add that the molecular detail of wax biodegradation requires further investigation.

“Wax is a polymer, a sort of ‘natural plastic’ and has a chemical structure not dissimilar to polyethylene,” said Spanish National Research Council's bee keeping Bertocchini, the study’s lead author.

The researchers conducted spectroscopic analysis to show the chemical bonds in the plastic were breaking. The analysis showed the worms transformed the polyethylene into ethylene glycol, representing un-bonded ‘monomer’ molecules.

To confirm it wasn’t just the chewing mechanism of the caterpillars degrading the plastic, the team mashed up some of the worms and smeared them on polyethylene bags - which continued to degrade.

“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,” said Bombelli.

“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.”

As the molecular details of the process become known, the researchers say it could be used to devise a biotechnological solution on an industrial scale for managing polyethylene waste.

Added Bertocchini: “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.”

Picture: OK - it turns out the caterpillar may well be very hungry but it is not the munching that degrades plastic it's the enzymes (or something else still to be discovered)

Article written by Cathryn Ellis | Published 05 May 2017

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