A Circular Bioprocess for the Sustainable Conversion of Polyethylene Terephthalate to Muconic Acid with an Engineered Pseudomonas Putida

Many studies have highlighted the role of biosynthetic pathway for the valorization of polyethylene terephthalate (PET) waste. However, the existing chemical or enzymatic methods employ additional catalyst to degrade polymer before biotransformation of the degradation products, leading to the increase in process cost and complexity. In this study, we created a circular bioprocess for the sustainable upcycling of PET to high-value added product muconic acid (MA) with regeneration of biocatalyst. We constructed a multifunctional Pseudomonas putida KT2440 by metabolic engineering to simultaneously secret PET hydrolase LCC and synthesize MA from terephthalate in the same fermentation process. Ingeniously, MA and extracellular enzyme LCC can be separated from the fermentation fluid by ultrafiltration, and the latter was re-used for the next round of PET hydrolysis. Another PET hydrolysate ethylene glycol can support the cell growth during fermentation, which further improves the resource utilization of PET waste. 0.50 g MA was produced from 1 g PET in each cycle, reaching 68% of the theoretical conversion. This biological and circular process with the reproduced PET hydrolase should have advantageous over existing PET upcycling processes and may applied in the valorization of other plastics or biomass resources such as lignin.