Divergent anaerobic fates of biodegradable plastics in landfill leachate

Biodegradable plastics (BPs) are increasingly promoted as sustainable alternatives to conventional polymers, yet their fate in landfills remains poorly understood. Here, we evaluated the anaerobic biodegradability of three BPs, polyhydroxybutyrate (PHB), poly(lactic acid) (PLA), and poly(butylene adipate-co-terephthalate) (PBAT), in landfill leachate under mesophilic conditions by quantifying carbon conversion to biogas. The BPs exhibited sharply contrasting degradation trajectories: PHB mineralized completely within 17 d, whereas PLA underwent substantial mineralization over 320 d (83.6%), extending beyond the well-established expectation of limited mesophilic degradation. In contrast, PBAT remained largely recalcitrant. Multi-omics analyses linked PHB and PLA depolymerization to the biofilm–polymer interface, with depolymerase transcription tracking their distinct degradation phases. Putative depolymerase homologs were widespread across recovered bacterial genomes, yet only a subset showed transcriptional support. This active fraction included multiple under-characterized lineages outside the taxonomic range of experimentally validated degrader genomes, revealing a marked disconnect between genomic potential and realized activity. Our findings show that anaerobic biodegradation outcomes in landfill leachate cannot be inferred from biodegradability labels or genomic potential alone, but emerge from polymer-specific depolymerization constraints and depolymerase transcription enriched at the biofilm–polymer interface. How different biodegradable plastics break down within landfills, particularly landfill leachate, remain unclear. Here, they evaluated the anaerobic biodegradability of three BPs, polyhydroxybutyrate (PHB), poly(lactic acid) (PLA), and poly(butylene adipate-co-terephthalate) (PBAT), using a combination of genome-resolved multi-omics.