Potential role of Galleria mellonella larval microbiota in polyethylene biodegradation

Rapid biodegradation of low-density polyethylene (LDPE) by the insect larvae Galleria mellonella motivates the understanding of the role of the larval microbiota in this process. In this study, the effect of the LDPE ingestion by these animals under normal or reduced microbiota conditions was evaluated and a rigorous protocol was designed to assess the gut and salivary glands microbial communities from G. mellonella larvae submitted to different diets. Microbiota depleted larvae showed decreased of LDPE consumption and their frass and cocoon presented changes in chemical features when compared to control larvae. High-throughput sequencing of 16S rRNA gene and ITS region reveled that beeswax-fed and LDPE-fed larvae exhibit similar bacterial community compositions, with an increased abundance of LDPE-biodegrading genera (Rhizobium and Sphingobium) in gut and salivary glands. Additionally, we report for the first time the presence of archaeal communities in both organs, and fungal communities in the salivary glands of G. mellonella. In beeswax-fed larvae, the phylum Ascomycota, known to include genera associated with PE biodegradation, was predominant. Another novel finding is the identification of the ciliate Aspidisca in salivary glands of beeswax-fed larvae, previously reported as a hydrocarbon-biodegrader. Functional prediction analysis demonstrated several enzymes potentially involved in LDPE digestion and allowed us to propose a hypothetical PE biodegradation pathway in G. mellonella larvae, involving a synergistic interaction between larval and microbial enzymes. Our results suggest that feeding on LDPE or beeswax selectively enriches microorganisms associated with hydrocarbons and LDPE biodegradation, indicating the innate capability of G. mellonella to biodegrade plastics.