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

Abstract

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.

Plastic biodegradation: do Galleria mellonella larvae - bio-assimilate polyethylene? A spectral histology approach using isotopic labelling and infrared microspectroscopy

“…24 Lemoine reported a 50% weight low on a PE diet. 25 Our results suggested that a pollen-only diet is sufficient for the survival of the larvae and that an additional source of carbon such as beeswax allows larvae to gain weight, in agreement with the literature 17,14 . L2-L3 larvae fed with pollen and PE survived 16 days and gained some weight but far less than the larvae fed with the optimal diet.…”

Enterococcus innesii sp. nov., isolated from the wax moth Galleria mellonella

“…It has the advantages of being inexpensive, easy to use, and able to grow at 37 °C, while not being subject to the same regulations and ethical concerns as mammalian models such as mice [15–17]. It has also been of interest due to the ability of the larvae to metabolize polyethylene [18]. Previous research on endogenous Galleria and Enterococcus species indicates these bacteria may have a colonization-resistance function, either passively or actively, through the production of antimicrobial bacteriocins [11, 19].…”

Worming the Circular Economy for Biowaste and Plastics: Hermetia illucens, Tenebrio Molitor and Zophobas morio

“…While plastics do not occur naturally, nature has a solution to man's artificial problem in the insects. These biological expertise include: Tenebrio molitor [36][37][38], Zophobas morio [35,36,39] and waxworms (Galleria mellonella L.) [40,41] to utilize PS and PE for mineralization [35,36,[39][40][41] as a carbon source. Fully digested, their frass can be utilized as natural fertilizers.…”