Role of the intestinal microbiome in polyethylene degradation by caterpillar larva of the greater wax moth (Galleria mellonella)

Recently, a few insects, including the caterpillar larva of the greater wax moth Galleria mellonella, have been identified as avid "plastivores". Interestingly, 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 are reduced by antibiotic treatment. Further, while the gut bacterial communities remain relatively stable regardless of diet, we show that during the early phases of feeding on LDPE (24-72 hrs), caterpillars exhibit 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 one year, we identified microorganisms in the genus Acinetobacter that appear 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.