Molecular-Weight-Dependent Degradation of Plastics: Deciphering Host-Microbiome Synergy Biodegradation of High-Purity Polypropylene Microplastics by Mealworms.

The biodegradation of polypropylene (PP), a highly persistent nonhydrolyzable polymer, by has been confirmed using commercial PP microplastics (MPs) ( 26.59 and 187.12 kDa). This confirmation was based on the reduction of the PP mass, change in molecular weight (MW), and a positive ΔδC in the residual PP. A MW-dependent biodegradation mechanism was investigated using five high-purity PP MPs, classified into low (0.83 and 6.20 kDa), medium (50.40 and 108.0 kDa), and high (575.0 kDa) MW categories to access the impact of MW on the depolymerization pattern and associated gene expression of gut bacteria and the larval host. The larvae can depolymerize/biodegrade PP polymers with high MW although the consumption rate and weight losses increased, and survival rates declined with increasing PP MW. This pattern is similar to observations with polystyrene (PS) and polyethylene (PE), ., both and decreased after being fed low MW PP, while and/or increased after high MW PP was fed. The gut microbiota exhibited specific bacteria associations, such as sp. and sp. for high MW PP degradation, sp. for medium MW PP, and sp. alongside three other bacteria for low MW PP metabolism. In the host transcriptome, digestive enzymes and plastic degradation-related bacterial enzymes were up-regulated after feeding on PP depending on different MWs. The host exhibited both defensive function and degradation capability during the biodegradation of plastics, with high MW PP showing a relatively negative impact on the larvae.