Polyvinyl chloride depolymerization and dechlorination by Tenebrio molitor larva-derived bacteria

Polyvinyl chloride (PVC), a persistent and ecotoxic plastic, poses severe environmental risks. In this study, two bacterial strains, Acinetobacter sp. PVC-6A and Bacillus sp. PVC-6B, were isolated from Tenebrio molitor gut. These two isolates were able to utilize PVC (M_n 28 kDa, M_w 64 kDa, M_z 110 kDa) as the sole carbon source, causing respective 2.55 % and 2.51 % weight loss of additive-free PVC films (1 cm × 1 cm) after 35 days of incubation at 30°C and pH 7.2. PVC degradation by both isolates was confirmed by multimodal characterization, including SEM, AFM, ATR-FTIR, and WCA. GC-MS analysis detected a novel chlorinated intermediate, 1-chlorohexadecane, along with multiple medium- and long-chain fatty acids, suggesting a partial dechlorination process during PVC depolymerization. This chlorinated intermediate supported the growth of strain PVC-6A and released nearly stoichiometric chloride ions, demonstrating further metabolic dechlorination. This pathway, which proceeds via multi-step dechlorination, is distinct from previously proposed PVC degradation mechanisms. Genomic and transcriptomic analyses identified a catalase-peroxidase (CAT) and two laccases (LAC1, LAC2) as key enzymes involved in PVC degradation. Recombinant enzyme treatments caused PVC depolymerization and dechlorination, with LAC1 exhibiting the highest activity, yielding a 13.1 % reduction in molecular weight and 77 % surface dichlorination (³⁵Cl^-). Molecular docking with AlphaFold3-predicted structures elucidated enzyme-plastic interactions. By revealing a novel PVC biodegradation pathway, identifying depolymerizing enzymes, and providing preliminary insights into enzyme-substrate binding, this study advances our comprehension of PVC biodegradation. It thereby establishes a theoretical foundation for developing bio-enzymatic remediation strategies against this persistent chlorine-releasing pollutant.