The role of microbial metabolic engineering for circular plastics economy.

The transition toward a circular plastics economy focuses on transformative innovations that decouple plastic production from fossil resources and mitigate environmental contamination. Central to this paradigm is the dual role of microorganisms in enabling sustainable plastic management: microbial and enzymatic degradation of recalcitrant fossil-based plastics and microbial synthesis of bioplastics. Recent advances in biotechnology have illuminated promising pathways for both. However, the plastic-degrading efficiency and bioconversion capacity of wild-type microorganisms remain insufficient for industrial applications, necessitating metabolic engineering to develop high-performance microbial cell factories. Breakthroughs in enzyme engineering have enhanced the properties of plastic-degrading enzymes, enabling polyethylene terephthalate (PET) degradation at pilot scale and paving the way for enzymatic recycling. Concurrently, novel microbial strains capable of efficiently converting renewable feedstocks into high-performance bioplastics, such as polyhydroxyalkanoates (PHAs) have been identified and genetically fine-tuned. Metabolic engineering strategies have enabled enhanced yield, altered polymer composition, and reduced process costs, significantly advancing the commercial viability of bioplastic production. Despite these strides, persistent challenges related to enzyme stability, catalytic efficiency, and economic scalability remain, demanding integrated solutions through strain engineering, process innovation, and system design. This review consolidates the state of the art in microbial and enzymatic plastic degradation technologies and metabolic engineering approaches for bioplastic synthesis, highlighting their synergistic potential to accelerate the realization of a truly circular and sustainable plastics economy. We conclude by outlining future research directions, emphasizing the necessity of interdisciplinary collaboration to overcome existing bottlenecks and unlock the full ecological and economic benefits of microbially driven plastic sustainability.