March 2021 – Issue 3(5)

How waxworms eat plastic By Harald Grove, M.Sc. Student & Sachi Villanueva, M.Sc. Student What you need to know Waxworms are the caterpillars of the greater wax moth, Galleria mellonella. These insects are common pests of apiaries and feed voraciously on honeycomb. Interestingly, they also voluntarily feed on polyethylene, a type of plastic commonly used in shopping bags. Because their natural diet of honeycomb is chemically similar to polyethylene, the waxworm may have evolved the necessary biochemical adaptations to degrade plastic wastes. Waxworm (Photo Credit: Rob Henderson)

Why this research is important How the research was conducted Global plastic production continues to increase due to the We fed waxworms polyethylene instead of their demand for cheap, durable, and versatile materials. honeycomb diet for several days. As the larvae devoured However, these characteristics make plastic resist the plastic sheet, their excretions changed and became degradation leading to accumulation in landfills and more liquid, indicating the presence of a different chemical marine ecosystems, negatively affecting our environment. waste. As one potential biodegradative product is a glycol, As a solution, research has focused on identifying we biochemically tested its presence in the excreta. Next, microorganisms like bacteria and fungi capable of plastic we analyzed the microbiome by treating the caterpillars biodegradation. When isolated, these microorganisms can with antibiotics to reduce their intestinal bacteria and then biodegrade plastics, albeit very slowly. However, when a measured the amount of glycol excreted. Additionally, we waxworm with an intact intestinal microbial community harvested and grew bacteria from the waxworm gut while (microbiome) consumes plastic, the biodegradation selecting for species capable of using polyethylene as a sole process is expedited. Our research solidifies the essential carbon source. We then extracted the bacterial DNA for partnership between the waxworm and its microbiome to sequencing and species identification. allow for polyethylene break-down and provides an To test for the involvement of the host in plastic additional research avenue to develop new methods of degradation, waxworms were either fed on their natural plastic bioremediation. honeycomb diet, polyethylene sheets, or were starved for

up to 72 hours. We then used RNA sequencing Further research should look at identifying and exploiting (transcriptome) analysis to assess global changes in gut the enzymatic machinery involved in this pathway. gene expression on these diets and looked for unique About the researchers categories related to metabolism. Finally, we measured Dr. Bryan Cassone, associate professor of Biology at total larval fat quantities to learn the consequence of Brandon University. [email protected] polyethylene degradation on energy stores. Dr. Christophe LeMoine, associate professor and Chair of What the researchers found the Department of Biology at Brandon University. The change in excreta that accompanied the transition [email protected] from a honeycomb to polyethylene diet indicated excretion Harald Grove (M.Sc. student), Sachi Villanueva (M.Sc. of glycol that decreased when larvae were fed antibiotics. student), Oluwadara Elebute (M.Sc.), and Charlotte Smith Additionally, polyethylene-fed waxworms had the highest (B.N., former research technician). microbial abundance of all three diets, showing that gut Publications based on the research bacteria were important for biodegradation. Further, we Cassone, B. J., Grove, H. C., Elebute, O., Villanueva, S. M. P., identified an Acinetobacter species of gut bacteria that & LeMoine, C. M. R. (2020). Role of the intestinal survived on polyethylene in culture for over a year. Overall, microbiome in low-density polyethylene degradation by our results showed the gut microbiome plays an integral caterpillar larvae of the greater wax moth, Galleria role in polyethylene degradation. mellonella. The Royal Society, 287(1922). Gene expression of the waxworm host revealed that many http://dx.doi.org/10.1098/rspb.2020.0112 digestive processes of honeycomb-fed caterpillars were LeMoine, C. M. R., Grove, H.C., Smith, C.M., & Cassone, B.J. similar in polyethylene-fed larvae suggesting normal (2020). A very hungry caterpillar: Polyethylene intestinal function on a plastic diet. Polyethylene-fed metabolism and lipid homeostasis in larvae of the greater larvae also showed a unique gene expression profile with wax moth (Galleria mellonella). Environmental Science an increased capacity for fat metabolism. Interestingly, a and Technology, 54(22), 14706–14715. direct measurement of fat quantities also showed http://dx.doi.org/https://doi.org/10.1021/acs.est.0c04386 increased fat retention in polyethylene-fed larvae. This demonstrates that the wax moth larva also plays a role in Keywords polyethylene degradation in synergy with their Biodegradation, microbiome, transcriptome, metabolism microbiome. While their normal metabolism is geared Acknowledgements towards deriving energy from bulky wax comb Research Connection is a periodical publication intended hydrocarbons, these pathways can be co-opted for the to provide information about the impact of Brandon degradation of synthetic polymers like polyethylene. University’s academic research and expertise on public How this research can be used policy, social programming, and professional practice. This This research provides evidence that aspects of microbial summary is supported by the Office of Research Services and animal metabolism work together during polyethylene and by the Centre for Aboriginal and Rural Education degradation. Enzymes from the animal and resident gut Studies, Faculty of Education. bacteria may be combined to develop a technology that Editor: Christiane Ramsey [email protected] may be used to degrade our plastic waste in the future. http://www.brandonu.ca/research-connection