Complete Enzymatic Depolymerization of Polyethylene Terephthalate (PET) Plastic Using a <i>Saccharomyces cerevisiae-</i>Based Whole-Cell Biocatalyst

Management of polyethylene terephthalate (PET) plastic waste remains a challenge. PET-hydrolyzing enzymes (PHEs) such as <i>Is</i>PETase and variants like FAST-PETase demonstrate promising PET depolymerization capabilities at ambient temperatures and can be utilized to recycle and upcycle plastic waste. Whole-cell biocatalysts displaying PHEs on their surface offer high efficiency, reusability, and stability for PET depolymerization. However, their efficacy in fully breaking down PET is hindered by the necessity of two enzymes: PETase and MHETase. Current whole-cell systems either display only one enzyme or struggle with performance when displaying larger enzymes such as the MHETase-PETase chimera. We developed a <i>Saccharomyces cerevisiae</i>-based whole-cell biocatalyst for complete depolymerization of PET into its constituent monomers with no accumulation of intermediate products. Leveraging a cellulosome-inspired trifunctional protein scaffoldin displayed on the yeast surface, we co-immobilized FAST-PETase and MHETase, forming a multi-enzyme cluster. This whole-cell biocatalyst achieved complete PET depolymerization at 30 °C, yielding 4.95 mM terephthalic acid (TPA) when tested on a PET film. Furthermore, we showed improved PET depolymerization ability by binding FAST-PETase at multiple sites on the scaffoldin. The whole cells had the added advantage of retained activity over multiple reusability cycles. This breakthrough in complete PET depolymerization marks a step toward a circular plastic economy.