Discovery and optimization of effective plastic depolymerizing enzymes

Today, only 20% of the nearly 400 million tons of global plastic production is recycled, leading to massive environmental pollution and unnecessary petroleum use. Polyethylene terephthalate (PET) is one of the most abundant plastics and is widely recycled by mechanical sorting and remelting into raw material for new product manufacturing. Recycled PET commands a lower in value than the virgin plastics due to a degradation in key properties, limiting its market and disincentivizing expanded recycling. Effective recycling of plastics requires selective and efficient degradation of polymeric plastics into monomers that can be interchangeable with virgin monomers made from oil. Because of their catalytic specificity and biological plasticity, enzymatic technologies have the potential to enable energy efficient recycling of both single use plastics and multicomponent materials. The DOE’s National Renewable Energy Laboratory (NREL) has demonstrated both biological and thermochemical routes for depolymerization of plastics into soluble components. For example, NREL has recently characterized enzymes that can selectively depolymerize aromatic polyesters and have further demonstrated the ability to engineer and augment these enzymes for better performance (Austin et al. 2017, PNAS). While these discoveries have established the feasibility of enzymatic plastic degradation, the current levels of activity are far below the requirements for an effective industrial process. Moreover, an integrated process must include all the steps (thermochemical and/or biochemical) required to selectively degrade plastic from recycled materials. In Phase I of this project we propose evolve effective enzymes for converting the plastic depolymerization products from thermochemical or biochemical process into useful monomers for manufacturing of new materials. Lead enzymes will be selected from previously discovered enzymes with a focus on thermophilic bacterial sources. Using chromogenic substrates synthesized by NREL, these lead enzymes will be diversified and screened for improved activity and specificity at elevated temperatures. Enzyme diversification approaches will include traditional random/rational directed evolution as well as Primordial Genetics’ proprietary Function Generator technology. The enzyme improvements resulting from these screens will be validated by NREL under process-relevant conditions using unmodified PET substrates. Phase I of this project will establish the potential to discover and evolve effective enzymes for plastic degradation into monomeric components. Subsequent R&D activities will complete the development of commercial enzymes as part of an integrated technology for plastic conversion and upcycling. Successful execution of this program and commercialization of this process will increase the adoption of PET recycling, lay the foundation for enzymatic recycling of other polymers and contribute to the development of a circular economy for plastics.