Engineering Microbial Systems for Plastic Biodegradation into Monomers to Bridge Natural Plastisphere Ecology with Industrial Circularity

Plastic pollution remains one of the most pressing environmental challenges of the twenty-first century. Global production reached 413.8 million tons in 2023 and 430.9 million tons in 2024, while annual post-consumer waste continues to approach 300 million tons. Conventional mechanical and chemical recycling routes remain limited in scale, efficiency, and applicability to mixed or contaminated streams. Microbial systems that enzymatically depolymerize synthetic polymers can, for hydrolyzable polyesters, release monomers under mild conditions and thereby support biological recycling. This review synthesizes the engineering of microbial systems for plastic depolymerization and monomer recovery, progressing from natural degraders and plastisphere communities through the redesign of enzymes and metabolic pathways to synthetic consortia and early industrial translation. PET hydrolases such as LCCICCG and TurboPETase achieve 90–98% conversion of pretreated, amorphized PET under high-solid loadings. Equivalent monomer recovery from untreated high-molecular-weight polyolefins has not been demonstrated. Bibliometric analyses document a sharp acceleration in research output after the 2016 discovery of Ideonella sakaiensis. Limitations in catalytic rate, substrate scope, assay standardization, environmental relevance, and process scalability are examined, and a framework is set out that links plastisphere colonization to engineered monomer recovery without equating surface enrichment or mass loss with complete biodegradation. Engineered microbial platforms can contribute to a circular plastics economy only if laboratory advances are validated under industrially and environmentally realistic conditions.