The Polymer-Plastisphere-Function Nexus Links to Divergent Biodegradation of Microplastics During Composting

Microplastic (MP) biodegradation is critical for mitigating plastic pollution, yet the ecological mechanisms linking polymer properties to plastisphere microbiome assembly and catalytic function remain unclear. Using thermophilic composting as an accelerated model, we reveal a fundamental dichotomy in which biodegradable MPs (BMPs: polylactic acid [PLA] > polybutylene succinate [PBS] > poly (butylene adipate-co-terephthalate) [PBAT]) undergo rapid thermophilic degradation shaped by stronger environmental filtering of diverse degraders, whereas conventional MPs (CMPs: low-density polyethylene [LDPE]) exhibit delayed degradation with greater stochastic influence. Metagenomics uncovered 489 degradative genes predominantly distributed across uncultured taxa, enabling reconstruction of polymer-specific multi-enzyme pathways, supported by isolating 32 potential degraders (31 candidate novel). PLA/PBS degradation primarily relied on thermophilic-phase PLA depolymerase and cutinase, PBAT on late-stage polyesterase and PETase, and LDPE on alkane monooxygenase and laccase. Statistical modelling showed BMP degradation strongly associated with plastisphere-physicochemical interactions (> 90% variance), whereas CMP appeared primarily constrained by material properties (e.g., degrader succession in PLA, enrichment in PBS/PBAT, and high molecular weight in LDPE). Functionally dominant degraders (1.9% of total microbes) were estimated to contribute 52.4%–80.6% of biodegradation efficiency. This work elucidates the core polymer-plastisphere-functional nexus underlying MP biodegradation during composting, providing a predictive framework and microbial resource for targeted remediation.