A Very Hungry Caterpillar: Polyethylene Metabolism and Lipid Homeostasis in Larvae of the Greater Wax Moth (Galleria mellonella)

Larvae of the greater wax moth (Galleria mellonella) possess the remarkable ability to consume and rapidly degrade low-density polyethylene. Previous studies have investigated the involvement of the animal's microbiome, but little is known about the host's actual role and if it benefits from biodegradation of this synthetic polymer. We used a combination of RNA sequencing and biochemical approaches to assess caterpillars fed honeycomb, fed polyethylene (PE), or starved for up to 72 h. Sequencing of gut transcripts revealed PE-fed larvae retain an expression profile consistent with normal intestinal function but also show distinct molecular signatures indicative of enhanced fatty acid metabolism (FAM). Further, quantification of total lipid content validated the impact of a PE diet on FAM; in contrast to lipid-depleted starved animals, PE-fed caterpillars maintain lipid reserves similar to honeycomb-fed larvae. Additionally, we found the activity of putative enzymes involved in lipid oxidation (e.g., alcohol dehydrogenase) are considerably higher in PE-fed larvae, indicating that on a functional level, these caterpillars are inducing pathways to effectively metabolize PE. Overall, we put forward a hypothesized model where the similarity in chemical structure between PE and its natural honeycomb diet has endowed larvae of G. mellonella with the extraordinary capability to derive energy from PE as an exclusive food source through pre-existing metabolic pathways.