Engineered Halomonas sp. Y3 enables highly efficient upcycling of poly(ethylene terephthalate) to polyhydroxyalkanoates.

The global plastic crisis demands innovative solutions for recycling polyethylene terephthalate (PET), a chemically stable polymer constituting 23 % of annual plastic waste. This study presents a significant advance in PET upcycling using engineered Halomonas sp. Y3, a halophilic bacterium uniquely suited for industrial bioprocessing. We addressed key challenges in PET valorization-inefficient assimilation of its depolymerized monomers, terephthalic acid (TPA) and ethylene glycol (EG)-through systematic metabolic engineering. First, TPA catabolism was enabled by integrating heterologous tph operons and transporters, achieving a 46 % higher TPA degradation rate (1.39 mmol/L·h) than Comamonas sp. E6 of 0.95 mmol/L·h. Concurrently, EG utilization was enhanced 6.3-fold (8.34 mmol/L·h) via glcDEFG overexpression and glyoxylate pathway optimization than wild-type Halomonas sp. Y3 (1.32 mmol/L·h). To overcome metabolic interference in single-strain systems, we pioneered a synthetic microbial consortium (PET_co) comprising two specialized Halomonas strains: one metabolizing EG and the other TPA. This consortium achieved complete co-utilization of mixed PET hydrolysates within 36 h, yielding 7.99 g/L polyhydroxyalkanoates (PHA)-2.4 × higher than monoculture controls (PET03, PET07, PET09)-without supplemental carbon. Notably, the strain halotolerance and alkaliphily enabled direct integration with alkaline PET depolymerization, bypassing costly sterilization. By synergizing chemical and biological processes, this work establishes Halomonas sp. Y3 as a robust platform for industrial-scale plastic upcycling, advancing circular economy strategies to mitigate plastic pollution.