PETase Kubu enables near-complete enzymatic depolymerization of commercial PLA/PBAT blend mulch film

Abstract

Agricultural mulch films improve crop productivity, but post-use recovery and recycling remain difficult because the films are thin, fragmented, dispersed across fields, and contaminated. Commercial PLA/PBAT blends are increasingly used as biodegradable mulch film materials, yet these films exhibit slow or incomplete degradation under environmental conditions. Here, we show that Kubu, a thermostable PETase from Kutzneria buriramensis, rapidly depolymerizes commercial PLA/PBAT mulch film without pretreatment at 60 {degrees}C, achieving 95% mass loss within 96 h and releasing terephthalate, adipate, and lactate, detected by LC-MS/MS and HPLC, as the major monomeric products of both PBAT and PLA components. GPC and SEM revealed extensive degradation at the polymer-water interface. DiffDock docking against Kubu, IsPETase, and TfCut indicates that the canonical W/F(Y) cleft of the PETase/Cutinase fold accommodates aliphatic and aromatic ester bonds with comparable geometry, suggesting that substrate promiscuity is an inherent property of the cleft architecture. Kubus distinctive contribution combines this permissive cleft with catalytic activity sufficient for near-complete blend depolymerization within 24 h. Integration with a socioeconomic analysis shows that complete enzymatic depolymerization could avoid social costs up to $4,087 per ton of mulch film. These findings establish a single-enzyme approach to end-of-life management of heterogeneous polyester blends.