Harnessing fungal-bacterial teamwork for enhanced degradation of commercial polylactic acid/polybutylene adipate-co-terephthalate blend

Due to their poor degradability under natural conditions, extensive use of polylactic acid/polybutylene adipate-co-terephthalate (PLA/PBAT) blends in agriculture raises environmental concerns, calling for eco-friendly solutions. Here, the bacterium Achromobacter sp. FJ1-2L and the fungus Papiliotrema laurentii SNP7-2P were isolated from long-term mulched soils. Their coculture synergistically degraded a commercial PLA/PBAT blend containing CaCO 3 and talc, achieving 66% net weight loss after 30 days, far exceeding the sum of individual net weight loss (34%). Mechanistically, a cross-feeding-mediated synergistic model was proposed. Early in the coculture, SNP7-2P excreted organic acids via overflow metabolism, which sharply lowered the medium pH to 4.12, driving the dissolution and detachment of CaCO 3 from the blend and creating structural defects. Water infiltrated through these defects into the material, initiating non-enzymatic hydrolysis and driving bulk erosion. Concurrently, proteases and lipases acted on the polymer surfaces and shallow accessible regions, catalyzing ester bond hydrolysis. This spatial complementarity between internal non-enzymatic hydrolysis and surface enzymatic catalysis released oligomers and monomers. Notably, SNP7-2P secreted markedly higher levels of protease and lipase (14.8- and 29.1-fold those of FJ1-2L, respectively), indicating its dominant role in depolymerization. Subsequently, FJ1-2L efficiently assimilated the released depolymerization products (e.g., adipic acid, lactic acid, and 1,4-butanediol), alleviating product inhibition and sustaining the depolymerization activity of SNP7‑2P, thus constituting an effective positive feedback loop. This study reveals the cross‑feeding-mediated synergistic degradation mechanism and an acid-triggered filler-dissolution pathway that accelerates PLA/PBAT breakdown, offering a promising bioaugmentation strategy for blended plastic waste treatment.