Plastic bags are a bane of modern life. As you read this, nearly two million of them are being used around the world right now. By the time the year is over, this number will probably reach a trillion, ending up in landfills, oceans, streams, and the digestive tracts of marine animals. Over the years, scientists have been coming up with various solutions to tackle this problem, from devising ways to give it a second lease of life to making greener and more sustainable plastics. But nature might have a simpler solution: wax worms.
For anyone who keeps bees, wax worms, which are actually the larva of the wax moth, are parasites that feed on beeswax, causing damage to beeswax combs and in some cases, destroying weakened hives entirely. By chance, this led research author and amateur beekeeper Federica Bertocchini of the Institute of Biomedicine and Biotechnology of Cantabria in Spain to stumble upon the caterpillars' unexpected ability to chew through and actually digest plastic.
They had made short work of the plastic bag she had placed them in, which became riddled with holes after just 40 minutes (that's about two holes per worm every hour) and turned it into a gaping mess 12 hours later. Given that plastic bags take a notoriously long time to break down, this discovery could have important implications for helping get rid of the polyethylene plastic waste in landfill sites and oceans, say the researchers.
According to previous studies, it took 100 mealworms 24 hours to make their way through 39 milligrams of Styrofoam and the bacteria six weeks to break down a thin PET film with temperatures maintained at 86 degrees Farenheit (30°C) – a rate scientists estimate to be around 0.13 milligrams per day. A group of 100 wax worms, on the other hand, munched through 92 milligrams of plastic in just half a day.
What's worth noting is that they were able to keep digesting polyethylene even when they were nothing more than mush. The researchers had wanted to be sure that the caterpillars were digesting the plastic and not just chewing their way out of the bag so they mashed some of them up and smeared the resulting paste on the bags, which degraded around 13 percent of the plastic. An analysis of the degraded plastic showed that the caterpillars had transformed the polyethylene into ethylene glycol – proof that they had digested it.
"The caterpillars are not just eating the plastic without modifying its chemical make-up," says co-author Paolo Bombelli, a biochemist at the University of Cambridge. "We showed that the polymer chains in polyethylene plastic are actually broken by the wax worms."
How exactly do the wax worms do it? The researchers believe this probably has something to do with the fact that polyethylene and the beeswax that the caterpillars normally feed on share a similar chemical structure. Hence, it is likely that digesting beeswax, which contains a diverse mixture of lipid compounds, and polyethylene involves breaking down similar types of chemical bonds.
"Wax is a polymer, a sort of 'natural plastic,' and has a chemical structure not dissimilar to polyethylene," explains Bertocchini.
So does this mean that wax worms will be a fixture in landfills in the future? Not really. Landfills are anaerobic environments and the lack of oxygen means that the bugs won't be able to survive in these places. Rather, the scientists are hoping to identify and isolate the wax worms' plastic-degrading enzymes so that they can be scaled up and used in industrial applications.
"The caterpillar produces something that breaks the chemical bond, perhaps in its salivary glands or a symbiotic bacteria in its gut," says 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. If a single enzyme is responsible for this chemical process, its reproduction on a large scale using biotechnological methods should be achievable."
The study was published in Current Biology.
Source: University of Cambridge
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