Complete digestion/biodegradation of polystyrene microplastics by greater wax moth (Galleria mellonella) larvae: Direct in vivo evidence, gut microbiota independence, and potential metabolic pathways

Biodegradation of plastic polymers by plastic-eating insects such as the greater wax moth (Galleria mellonella) might be promising for reducing plastic pollution, but direct in vivo evidence along with the related metabolic pathways and role of gut microbiota require further investigation. In this study, we investigated the in vivo degradation process, underlying potential metabolic pathways, and involvement of the gut microbiota in poly-styrene (PS) biodegradation via enforcing injection of G. mellonella larvae (Tianjin, China) with PS microbeads (0.5 mg/larva; M-n: 540 and M-w: 550) and general-purpose PS powders (2.5 mg/larva; M-n: 95,600 and M-w: 217,000). The results indicated that the PS microplastics were depolymerized and completely digested independent of gut microbiota in G. mellonella although the metabolism could be enhanced by gut microbiota. Based on comparative metabolomic and liquid chromatography analyses, we proposed two potential metabolic path-ways of PS in the intestine of G. mellonella larvae: the styrene oxide-phenylacetaldehyde and 4-methylphenol-4-hydroxybenzaldehyde-4-hydroxybenzoate pathways. These results suggest that the enzymes of G. mellonella are responsible for the efficient biodegradation of PS. Further study is needed to identify these enzymes and investigate the underlying catalytic mechanisms.

Automated summary

Plastic-eating insects like the greater wax moth show promise in reducing plastic pollution through biodegradation, with the potential for enhanced metabolism with the involvement of gut microbiota. This study found that polystyrene microplastics can be depolymerized and digested in greater wax moths independently of gut microbiota, indicating efficient biodegradation by the insects' enzymes. Proposed potential metabolic pathways for polystyrene degradation in the insects' intestines provide insight for further research on enzyme identification and catalytic mechanisms.