Biodegradation of polypropylene by yellow mealworm ( <i>Tenebrio molitor</i> ) larvae: response of gut microbiome and metabolome to plastic polymers

The widespread use and improper disposal of polypropylene (PP) facemasks have resulted in persistent environmental pollution, posing urgent challenges for waste management. This study added bran-PP mixture, which increased the survival rate, consumption rate and removal rate of Tenebrio molitor feeding solely on PP. The average consumption of the larvae fed with the edible bran-PP mixture was 61.54% higher than those fed only PP. The removal rates were 39.26% and 36.14%, respectively. Fourier-transform infrared spectroscopy, thermal gravimetric analysis, gel permeation chromatography, and nuclear magnetic resonance confirmed the production of oxygenated compounds in the larval gut, indicating partial oxidation and degradation of PP masks within the intestinal tract. HT-GPC analysis revealed significant reductions in molecular weight parameters, with the number-average (Mn), weight-average (Mw), and Z-average (Mz) molecular weights decreasing by 51.07%, 33.60%, and 32.99%, respectively. High-throughput 16S rRNA sequencing revealed that feeding on PP enhanced gut microbiota richness and diversity. The bran-PP mixture group exhibited significantly higher relative abundances of Enterobacter and Spiroplasma, whereas the bran group was dominated by Lactobacillus. PICRUSt functional predictions indicated upregulation of plastic degradation-associated oxidases (alkane 1-monooxygenase, cyclohexanone monooxygenase) and hydrolases (chitinase, carboxylesterase) in larvae fed PP or bran-PP diets. Metabolomic profiling revealed significant enrichment in pathways related to histidine, glycerophospholipid, choline and steroid hormone metabolism in PP-fed larvae. These findings demonstrate that PP can be biodegraded in T. molitor larvae through gut microbe-mediated depolymerization involving a diverse microbial community.