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Monday
May012017

A Plastic Eating Caterpillar: An Accidental Discovery with Potential?

Humans produced 311 million tons of plastic in 2014, and that number is expected to double in the next two decades. About 40 percent of this is plastic bags, containers, and other products made of polyethylene [2]. Much of this plastic is discarded in landfills, and new solutions for plastic degradation are urgently needed.
Federica Bertocchini, a beekeeper and researcher in Spain, found her hives infested with waxworms, a type of caterpillar that feeds on beeswax. She placed the worms in a plastic bag while she cleaned out the hives, and when she returned to the bag, it was full of holes! Surprised, Bertocchini created a waxworm homogenate and applied that to a polyethylene plastic bag. After half a day, the bag had about 13% less mass, demonstrating that the breakdown was not purely mechanical. She worked with biochemists at the University of Cambridge to analyze the chemistry more closely. They determined using FTIR that polyethylene treated with worm homogenate had ethylene glycol present, suggesting that the polyethylene was being broken down into ethylene glycol.   
 
Other organisms with plastic degrading abilities have been discovered in recent years. In 2016, a Japanese team identified a bacterium that can degrade polyethylene terephthalate [5]. In 2014, Chinese scientists found that two species of bacteria from the gut of Indian mealmoths can degrade polyethylene. However, these microbes worked over the course of weeks or months [3]. Federica’s waxworms shredded polyethylene shopping bags within hours.
 
Bertocchini believes the waxworms may have evolved an ability to degrade polyethylene because of its carbon bond similarity to wax. Others are not convinced of the waxworm’s promise. Ramani Narayan says that the degradation, even if it is producing ethylene glycol, is “not a magical solution to plastics waste management”. The worms could pass microplastics into the environment and transport these toxins up the food chain.
 
Bertocchini says that the application of these worms could stem from identifying the enzymes that are actually degrading the polyethylene. Researchers do not know what exactly allows these worms to degrade polyethylene. The responsible enzyme could then be produced at high volumes, rather than using millions of actual worms. This wax worm discovery is still far from a solution to our planet’s growing piles of plastic, but I hope it can lead to an advancement with a real environmental impact.
 
--CJW
                                                                                                                       
References
1. Bombelli P, Howe CJ, Bertocchini F. Polyethylene bio-degradation by caterpillars of the wax moth Galleria mellonella. Current Biology. April 2017.
2. Neufeld L, Stassen F, Sheppard R, Gilman T. The New Plastics Economy: Rethinking the future of plastics. World Economic Forum. January 2016.
3. Yang J, Yang Y, Wu WM, Zhao J, Jiang L. Evidence of polyethylene biodegradation by bacterial strains from the guts of plastic-eating waxworms. Environ. Sci. Technol. November 2014.
4. Yong E. The Very Hungry Plastic-Eating Caterpillar. The Atlantic. April 24, 2017.
5. Yoshida S, Hiraga K, Takehana T, Taniguchi I, Yamaji H, Maeda Y, Toyohara K, Miyamoto K, Kumura Y, Oda K. A bacterium that degrades and assimilates poly (ethylene terephthalate). Science. March 2016.
 
Images: Wayne Boo/ USGS Bee Inventory and Monitoring Lab (waxworm)
Federica Bertocchini (waxworm chewing plastic)