(265d) Complete Enzymatic Depolymerization of Polyethylene Terephthalate (PET) Plastic Using a Saccharomyces Cerevisiae-based Whole-Cell Biocatalyst

A promising solution to the challenge of polyethylene terephthalate (PET) waste management is enzymatic depolymerization. PET can be completely depolymerized into its constituent monomers- terephthalic acid (TPA) and ethylene glycol (EG) - through enzymatic methods. However, complete PET depolymerization at ambient temperature requires the synergistic action of two enzymes - PETase and MHETase.

Whole-cell biocatalysts have shown promising PET depolymerization performance and have exhibited advantages of reduced enzyme aggregation, improved enzyme stability and reusability. However, existing whole cell systems for PET depolymerization either display only one enzyme efficiently on their surface or show limited capabilities with display of larger passengers like the MHETase-PETase chimera. Thus, complete PET depolymerization remains challenging in such systems.

In this work, we developed a Saccharomyces cerevisiae-based whole-cell biocatalyst system capable of achieving complete PET depolymerization. FAST-PETase and MHETase were attached to a trifunctional protein scaffoldin displayed on the yeast cell surface, to form a multi-enzyme cluster. This trifunctional scaffoldin facilitated the maintenance of excess FAST-PETase on the scaffold relative to MHETase. The whole-cell biocatalyst exhibited complete PET depolymerization at 30°C with high efficiency, with TPA yields of 5000 µM within 96h when tested on a PET film substrate. The whole cell biocatalysts exhibited reusability over multiple cycles. The monomers thus obtained can be subsequently upcycled into useful products. This complete depolymerization of PET to its constituent monomers is an important step to achieve a circular plastic economy.