Recipient Organization
The Regents of University of California
200 University Office Building
Riverside,CA 92521
Performing Department
(N/A)
Non Technical Summary
Because of the low costs to manufacture, plastics have been widely used in agricultural and food systems, especially for food packaging.Polyethylene terephthalate (PET), a polyester plastic, is the most widely used plastic material for food packaging. The production and use of PET for food packaging are constantly increasing at a rate of 5.2% worldwide.Because PET is non-biodegradable, it can take years to degrade when discarded into the environment. Plastic pollution has received much attention and become a major environmental issue. Although some strategies (e.g., prevention measures, clean-up activities, and awareness instruments) have been raised, it is still not feasible to remove discarded plastics from the environment and fix the existing widespread plastic pollution. In recent years, chemical recycling of PET waste has been actively studied.For chemical recycling, PET polymers are broken down to their monomers of terephthalic acid (TPA) and ethylene glycol (EG) that can be refined or re-manufactured into high-value products, but these methods have several disadvantages, including high cost, complicated processing steps, and poor compatibility with down-stream refined processes.To perform an environmental-friendly and green depolymerization of PET waste, the discovery of plastic-degrading enzymes has opened a new avenue for PET degradation and recycling.?
Animal Health Component
40%
Research Effort Categories
Basic
20%
Applied
40%
Developmental
40%
Goals / Objectives
In this project, we aim to engineer yeast surfaces to display plastic-degrading enzymes to degrade waste PET bottles. The expressed enzymes on yeast surfaces can be programmed to achieve a high biocatalytic activity to degrade PET waste. In this study, we will engineer yeasts (Saccharomyces cerevisiae, EBY100) to display two PET-degrading enzymes (PETase and MHETase) that can break down PET waste into its original monomers (TPA and EG). Under optimal conditions, we will then test the engineered yeasts to degrade commercial PET bottles in bioreactors, such as Coca-Cola, Pepsi-Cola, and Dasani bottles. The products (TPA and EG) will be recycled using downstream processes and quantified using high-performance liquid chromatography (HPLC). In addition, techno-economic analysis (TEA) will be applied to evaluate the economic feasibility and identify the 'hot spot' to improve the economic performance of the proposed technology.
Project Methods
TheSpecific Aimsof this proposal are:Aim 1: Engineer yeast strains displaying various PETasemutand MHETasemuton their cell surfaces and evaluate their ability to degrade PET.Various PETasemutand MHETasemutwill be expressed on yeast surfaces (EY-PETasemutor EY-MHETasemut), respectively. The mutant enzymes expressed on the yeast surface will be characterized using flow cytometry and confocal microscopy. Afterward, their performances to degrade PET film will be determined based on the enzymatic products (TPA and EG). Engineered yeasts (EY-PETaseoptimalor EY-MHETaseoptimal) with the highest enzymatic activities for PET degradation will be used in the following aims.Aim 2: Engineer yeast strains displaying both PETaseoptimaland MHETaseoptimalthat can degrade PET with a high efficiency.To completely degrade PET waste to high-value monomers, both PETaseoptimaland MHETaseoptimalwill be co-expressed on the same yeast surface at different ratios. The expression of both optimal PET-degrading enzymes on the same yeast surface will be characterizedusing both flow cytometry and confocal microscopy. The capacity for degrading PET waste using these yeasts will be evaluated based on the enzymatic products (TPA and EG).Aim 3: Degrade waste PET bottles in bioreactors using engineered yeasts displaying optimal PET-degrading enzymes and then recover high-value products.An up-scaled test in bioreactors will be carried out to optimize the bioprocessing conditions, map out the technological pitfalls, and provide key parameters for performing the subsequent techno-economic analysis. To this end, the PET bioconversion process ranging from pretreatment to enzymatic degradation and final product recovery and purification will be demonstrated in a 10 L bioreactor.Aim 4: Apply techno-economic analysis (TEA) to evaluate engineered yeasts displaying plastic-degrading enzymes to degrade plastic waste.System-level TEA will be conducted to evaluate the economic feasibility of applying the proposed technology to convert PET waste into TPA and EG. The resulting TEA model will be continuously updated based on the experimental results and provide key information forprocess improvement from economic perspectives.