Recently, a few insects, including the caterpillar larva of the greater wax moth
Galleria mellonella
, have been identified as avid ‘plastivores’. These caterpillars are able to ingest and metabolize polyethylene at unprecedented rates. While it appears that
G. mellonella
plays an important role in the biodegradation process, the contribution of its intestinal microbiome remains poorly understood and contested. In a series of experiments, we present strong evidence of an intricate relationship between an intact microbiome, low-density polyethylene (LDPE) biodegradation and the production of glycol as a metabolic by-product. First, we biochemically confirmed that
G. mellonella
larvae consume and metabolize LDPE, as individual caterpillars fed on polyethylene excreted glycol, but those excretions were reduced by antibiotic treatment. Further, while the gut bacterial communities remained relatively stable regardless of diet, we showed that during the early phases of feeding on LDPE (24–72 h), caterpillars exhibited increased microbial abundance relative to those starved or fed on their natural honeycomb diet. Finally, by isolating and growing gut bacteria with polyethylene as their exclusive carbon source for over 1 year, we identified microorganisms in the genus
Acinetobacter
that appeared to be involved in this biodegradation process. Taken collectively, our study indicates that during short-term exposure, the intestinal microbiome of
G. mellonella
is intricately associated with polyethylene biodegradation
in vivo
.
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.
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