Chemical characterization and gut microbial response unveil modification of polystyrene polymer in the lesser mealworm.

The massive production of plastics, together with inadequate waste management, has intensified the problem of plastic pollution. Recently, the scientific community has increasingly investigated the interactions between plastic polymers and biological systems, with particular interest in plastivorous insects and their gut-associated microbial communities. The lesser mealworm Alphitobius diaperinus has emerged as a promising model for studying biological interactions associated with polystyrene (PS) modification during gut transit. In this study, two complementary approaches were applied to characterize gut mediated responses to PS. First, chemical analyses were employed to provide evidence of polymer modification following gut transit; micro-FTIR analysis confirmed the presence of PS residues in larval frass and showed detectable structural changes in the recovered material, while GC-MS analysis identified α-methylstyrene and cumyl alcohol as compounds associated with PS chemical modifications and not detected in controls. Second, gut microbiota composition was assessed through metabarcoding analysis using full-length PacBio HiFi sequencing of the 16S rDNA gene. Differences were observed between the microbiota of PS fed larvae and that of the control group under different experimental conditions. Together, these results indicate that PS ingestion leads to measurable chemical modifications of the polymer and shifts in gut microbial composition, providing insight into insect–microbe interactions associated with PS transformation.