Biological upcycling of polystyrene into ready-to-use plastic monomers and plastics using metabolically engineered Pseudomonas putida

Abstract

The persistent accumulation of plastic waste, particularly polystyrene (PS), poses significant environmental challenges because of its extensive use and low recycling rates. Addressing these challenges necessitates inno vative and sustainable solutions. This study presents a strategy to upcycle PS waste into valuable chemical products, including adipic acid, hexanediol, hexamethylenediamine, and nylon-6,6, using metabolically engi neered Pseudomonas putida KT2440. This process involves the photolytic degradation of PS into benzoic acid, followed by microbial conversion into cis,cis-muconate (MA) and chemical synthesis of the final products. The engineered strains withstood 30 mM concentrations of PS-derived aromatics and converted them stoichiomet rically into MA in the presence of glucose as a growth substrate. 13C metabolic flux analysis revealed energy and redox limitations in the presence of 25 mM benzoate and 300 mM MA. The cells responded to stress by enhancing the flux for periplasmic glucose oxidation and fluxes through the NADPH-forming dehydrogenases; this process caused more than 40 % glucose‑carbon loss into byproducts. Fine-tuned dynamic glucose and benzoate feeding enabled high-level MA production. Energy-optimized genome-reduced strains were used to increase carbon ef ficiency. A final MA titer of over 65 g L− 1 was achieved in fed-batch fermentation. This process was demonstrated using the glucose derived from a viscose textile waste blend as the growth substrate and resulted in fully waste based products. The resulting adipic acid and hexamethylenediamine were polymerized into nylon-6,6 with properties comparable to those of petrochemical-derived polymers, revealing a sustainable pathway for PS upcycling. This research provides a proof-of-concept for bacterial upgrading of PS-derived substrates and a viable method for managing plastic waste and producing valuable chemical products.