(27d) Polyethylene Terephthalate (PET) Plastic Intermediates Deconstruction in One Pot B. Subtilis Bioprocess

According to the U.S. Environmental Protection Agency, the plastics industry contributed 14 million tons of waste out of a total of 26. 8 million tons, a significant portion of which comes from Polyethylene Terephthalate. More commonly referred to as PET, it is lightweight plastic primarily used for packaging. While the U.S. currently recycles 31% of the consumed PET, it is not biodegradable through traditional methods, thus precipitating the need for an alternative recycling method. Furthermore, accumulation of PET has an ecological and environmental impact, especially on aquatic life. Therefore, developing strategies to utilize this abundant carbon source for making valuable products is vital. PET can be depolymerized into terephthalic acid and ethylene glycol; ethylene glycol has applications in refrigeration, air conditioner industry, etc. Several thermochemical treatments can carry out PET depolymerization. However, thermochemical treatments are energy-intensive, and using corrosive chemicals (catalysts) can contaminate water bodies. Enzymatic depolymerization is a precise, milder, and more benign method of PET depolymerization. Enzymatic hydrolysis leads to PET breakdown into terephthalate and ethylene glycol. These monomeric units can be used as utility chemicals in other industries; for example, ethylene glycol is used in freezing units and air conditioners and has a market value of 33 billion dollars in 2020. This project aims at secreting PET depolymerizing enzymes for synergistic in situ depolymerization of PET by the B. subtilis bacterial platform. Native SEC pathway signal peptides were used to develop PET hydrolyzing enzyme export machinery in B. subtilis microbial system. Our initial results demonstrate the in situ breakdown of the PET intermediate, bis(2-hydroxyethyl) terephthalate (BHET) through a one-pot process. Terephthalic acid titre of 7.1 g/L was obtained with 100% breakdown of BHET. Furthermore, in vitro studies conducted by using the supernatants of engineered strains showed the production of terephthalic acid from a PET substrate. Further developments in in situ PET plastic deconstruction processes can play a vital role in processing plastic waste and reducing the environmental pollution in the upcoming decade.