24 April 2017
Plastic-munching caterpillars may show us how to dissolve waste
César Hernández/CSIC
Caterpillars could hold the key to our growing problem of plastic waste. While doing some routine beehive maintenance, a team of researchers in Spain has chanced upon one type of caterpillar that seems to have a taste for the stuff.
Federica Bertocchini at the Institute of Biomedicine and Biotechnology of Cantabria was picking honeycomb moth caterpillars out of a beehive and placing the beeswax-eating pests in a plastic bag for disposal. After a while she found that the caterpillars had broken loose and were milling everywhere. She and her team later confirmed the caterpillars can eat through plastic, and they now want to develop a quick way of breaking down polyethylene – used to make plastic bags – with enzymes from the caterpillars.
The team found that 100 caterpillars of the Galleria mellonella moth can riddle a supermarket shopping bag with holes in under an hour, and can consume 92 milligrams of plastic in half a day – that’s just over 3 per cent of a shopping bag. “That’s quite fast,” says Bertocchini, considering that it takes at least 100 years for one to decompose naturally.
To make sure the caterpillars were actually digesting the plastic, the team ground some of them up and spread a thin layer of the paste on a polyethylene film. Within 14 hours and after some reapplications, the paste had broken down 13 per cent of the plastic. The team also found traces of ethylene glycol, a sign of polyethylene breakdown.
“Our study is the first scientific work to show that this species eats plastic with the chemical depolymerisation of polyethylene,” says Bertocchini. Such an ability might be down to the caterpillars harbouring certain gut microbes.
Wei-Min Wu from Stanford University, who has studied various plastic-eating species, says the results are exciting. But he says the paste has produced a much higher biodegradation rate than anything seen in polyethylene-degrading bacteria isolated so far, suggesting that what goes on in the caterpillar’s gut is more complicated.
Bertocchini is hoping that a single enzyme is what is breaking down the plastic. “If this is the case, I can picture a scenario in the future where we can isolate it, produce it on a large scale and use that to biodegrade plastics.” She has founded a biotech company with one of her co-researchers, but they don’t yet have the funds to test the idea.
They’re not the only ones working on this. BioCellection, start-up based in San Jose, California, is hoping to launch a pilot plastic waste-processing plant by 2020. Their plan involves chemically treating plastics to make them easier for bioengineered bacteria to digest.
In the meantime, it’s not unreasonable to think we will keep finding organisms that have evolved to digest plastic. But our plastic problem won’t magically go away. On the plus side, neither will these creatures start devouring our precious plastic goods.
“These animals don’t live on plastic,” says Bertocchini. “They eat it to get out of it, or get to the food behind it. If in the future something evolves to exclusively eat plastic, I don’t know. So far it hasn’t happened.”
Journal reference: Current Biology, DOI: 10.1016/j.cub.2017.02.060
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