Engineered Microbial Catalyst for Simultaneous Depolymerization and Upcycling of Polycaprolactone

Abstract

Plastic waste is a pressing global challenge. Although end-of-life plastics have long been regarded as an environmental burden, they also represent a vast yet underutilized carbon resource that could be redirected toward chemical production rather than discarded. Here we report an engineered microbial catalyst, PCL-DU, which enables one-pot biocatalytic depolymerization and upcycling of the plastic poly(ε-caprolactone) (PCL) into the high-value chemical adipic acid. PCL-DU integrates a cell surface catalytic depolymerization module based on curli nanofiber surface display of cutinase for extracellular PCL hydrolysis, and an intracellular biocatalytic cascade that converts the released monomer 6-hydroxyhexanoic acid (6-HHA) to adipic acid. This dual-functional microbial catalyst achieved complete one-pot conversion of PCL film to adipic acid under optimal conditions. In fed-batch operation, PCL-DU demonstrated catalytic robustness, maintaining activity over 9 days without the requirement for inducers or antibiotics, producing 12.07 ± 0.07 g adipic acid/L with a yield of 0.83 ± 0.00 g adipic acid/g PCL. Furthermore, we demonstrated the applicability of PCL-DU biocatalyst on real-world PCL products, achieving a conversion rate of 0.96 g adipic acid/L/day and a yield of 0.81 g adipic acid/g PCL. The recovered adipic acid was successfully polymerized into nylon-6,6, establishing a complete upcycling pathway from plastic waste to industrial polymer. In all, the dual-functional microbial catalyst achieved simultaneous biocatalytic depolymerization and conversion of PCL into high-value chemical adipic acid by spatially integrating extracellular enzymatic plastic depolymerization with intracellular biotransformation. This work provides a novel biocatalytic platform for advancing sustainable recovery and upcycling of plastic carbon.