Unveiling gut microbiota and metabolic functions contributed to polyvinyl chloride degradation in Spodoptera frugiperda larvae

The accumulation of synthetic plastic waste, particularly polyvinyl chloride (PVC), threatens ecosystems globally. While microbial biodegradation represents a sustainable solution, limited effective PVC-degrading microbial bioresources have been identified. Here, we investigated the gut microbiota of Spodoptera frugiperda larvae, revealing a consistent microbial profile dominated by Enterococcus in both gut contents and tissues. PVC film feeding induced significant microbiota shifts, with functional parallels to PVC powder-fed Tenebrio molitor larvae despite taxonomic divergence. Through enzyme-centric analysis, we found an Enterococcus casseliflavus strain from the gut of S. frugiperda larvae could encode a NAD-dependent oxidoreductase that directly dechlorinates additive-free PVC, representing the first case of enzymatic polymer dechlorination. This enzyme reduced PVC molecular weight (Mn: 12.02 %; Mw: 14.07 %) and notably liberated chloride ions (6.48 mg/L with NADH as a co-factor). Our findings demonstrate the PVC-degrading capacity of S. frugiperda gut microbiota and reveal its dechlorination mechanism, offering an enzymatic candidate for developing novel biocatalysts and engineered microbial strains for enhanced biodegradation. By unravelling insect-associated microbes and enzymes, this work lays a theoretical foundation for their application potentials in sustainable PVC wastes upcycling and microplastic remediation.