Plastic pollution constitutes one of the most pressing global environmental challenges, driven in particular by the pervasive dependency of modern society on plastic products across diverse economic sectors. Plastics as synthetic polymers permeate the various components of the human production and consumption system, including food packaging (36 % of total plastic production), electronics components (12 %), medical devices (8 %), and construction materials (16 %). The scale of plastic manufacturing reflects this reliance. Global plastic output soared from 234 million tons (Mt) in 2000 to 460 Mt. in 2019. If current annual growth rates of 3.5 % continue, production is expected to reach 1.1 billion tons by 2050 (Wang et al., 2024b). Alarmingly, almost 40 % of these plastics are single-use products with a lifespan of less than 30 days, which significantly contribute to the accumulation of plastic waste. This pattern reveals an inherent conflict between the prevailing linear economic paradigm and the enduring environmental persistence of plastic materials. For example, a polyethylene terephthalate (PET) bottle requires over 400 years to mineralize completely. Meanwhile, the issue is particularly pronounced in developing regions of East and Southeast Asia, where waste management and recycling infrastructure covers less than 30 % of the population. Consequently, an estimated 8–12 Mt. of plastic is discharged into the oceans annually via riverine transport, a figure projected to double by 2030 if current trends persist (Lebreton et al., 2017; Mustafa et al., 2025). Marine fauna frequently experiences fatal outcomes due to plastic ingestion, which also introduces toxic substances into aquatic ecosystems (Fig. 1). Additionally, microplastics (MPs, < 5 mm in diameter) are also generated and incorporated into global biogeochemical cycles (Thompson et al., 2024). These particles have been detected in remote ecosystems as well as in commonly consumed items such as drinking water and table salt (Allen et al., 2019). More concerningly, medical research indicates that MPs can penetrate the blood-brain barrier, potentially elicit inflammatory responses and disrupt endocrine signaling, thus posing significant long-term risks to human health (Nihart et al., 2025). In response to this transboundary and complex pollution crisis, international efforts are underway to establish a comprehensive governance framework under the Global Plastic Treaty.

PET is the second most extensively produced plastic globally, with an annual output surpassing 70 Mt., accounting for approximately 18 % of total plastic production. As a semi-crystalline thermoplastic polyester, PET is synthesized via the polycondensation of EG and TPA (Fig. 2), with a microstructure comprising highly ordered crystalline regions (30–50 % crystallinity) surrounded by randomly distributed amorphous zones (Taniguchi et al., 2019). The global management of plastic waste, particularly PET, still relies heavily on conventional disposal methods, incineration including incineration (∼12–34 %), landfilling (∼55–62 %), and recycling (∼9 %). (Geyer et al., 2017; Houssini et al., 2025). Incineration, although effective in reducing waste volume, generates hazardous emissions such as dioxins and substantial quantities of greenhouse gases (Baca et al., 2023). Landfilling, conversely, results in long-term accumulation of persistent pollutants due to PET's high chemical stability. To tackle these environmental issues, technologies for recycling have been advanced and are primarily categorized into mechanical and thermochemical recycling. However, recycling rates vary greatly by region, with PET recycling reaching ∼41 % in the European Union (European Parliament, 2023), ∼29 % in the United States (Napcor, 2023), and over 80 % in China (Ma et al., 2020). Mechanical recycling is currently the most widely employed approach; however, after three recycling cycles, intrinsic viscosity (IV) declines to 0.582 dL/g, resulting in a more than twofold decrease in mechanical performance. This method markedly reduces the commercial value of recycled PET and restricts its practical applications (Kim et al., 2024). Thermochemical recycling, conducted at 220–280 °C and 2–4 MPa, depolymerizes PET into a mixture of bis(2-hydroxyethyl) terephthalate (BHET), mono(2-hydroxyethyl) terephthalate (MHET), EG, and TPA. The process also generates toxic byproducts such as acetaldehyde, and the cost-intensive purification of monomers constitutes 60–70 % of total processing expenses. In contrast, biocatalytic degradation has emerged as a promising and environmentally sustainable alternative due to its operation under mild conditions. Cutinase, such as the leaf-branch compost cutinase (LCC), is a microbial enzyme capable of hydrolyzing ester bonds in PET. Through rational protein engineering, a thermostable variant, LCCICCG, was developed and shown to depolymerize over 90 % of amorphous PET into monomers within 10 h (Tournier et al., 2020). Furthermore, FAST-PETase, an engineered version of PETase guided by machine learning and structural analysis, was reported to effectively degrade 51 different post-consumer PET products within one week at temperatures below 50 °C and across a broad pH range (Lu et al., 2022). Notably, both enzymatic systems yield exclusively soluble monomeric products, offering a promising route toward a closed-loop PET recycling process.

Extensive studies have revealed that various microbial species inhabiting PET-contaminated environments (most notably Ideonella sakaiensis) have evolved specialized metabolic pathways encompassing the secretion of hydrolytic enzymes, enzymatic depolymerization of PET, uptake of degradation products, and their subsequent intracellular assimilation (Yoshida et al., 2016). These innate biocatalytic systems hold significant promise for in situ biodegradation of PET. Nonetheless, the native strains are constrained by inherent limitations, such as slow proliferation rates and stringent cultivation requirements, thereby impeding their feasibility for large-scale industrial applications. Accordingly, research efforts have increasingly shifted toward the detailed molecular characterization of these enzymes rather than the utilization of whole-cell metabolic systems. Recent progress in this domain emphasizes elucidating the microbe–PET interface dynamics and refining degradation conditions to augment biocatalytic efficiency. Synthetic biology approaches, particularly the construction of genetically engineered microbial systems recapitulating natural PET degradation pathways, have emerged as transformative strategies for PET waste valorization. Among the potential chassis organisms, Escherichia coli (E. coli) is especially advantageous due to its short doubling time, the availability of comprehensive genetic manipulation tools, and its robust capacity for heterologous protein expression. Furthermore, the versatile metabolic network of E. coli facilitates the seamless integration of downstream catabolic pathways responsible for the mineralization of TPA and EG, thereby coupling a synergistic approach that combines enzyme engineering with metabolic pathway optimization (Carniel et al., 2024).

This review offers a comprehensive evaluation of recent progress in employing genetically engineered E. coli as a versatile platform for expressing PET depolymerase. The discussion encompasses molecular optimization of mono-enzymatic systems, particularly PETase variants, through rational protein design and directed evolution to enhance both catalytic efficiency and thermostability. Building upon these advancements, we propose an integrated framework for the construction and characterization of multi-enzyme cascades, comparing the catalytic efficiency of freely dispersed enzyme consortia versus scaffold-organized multi-enzyme complexes. Furthermore, the development of whole-cell biocatalysts is addressed through the application of advanced surface display strategies, such as CsgA-based nanoscaffolds, which facilitate precise enzyme localization and significantly accelerate interfacial PET hydrolysis kinetics. Complementary metabolic pathway analysis elucidates the full assimilation routes for PET-derived monomers in engineered E. coli and prioritizes key targets for metabolic enhancement. Targeted interventions include the upregulation of catalytic nodes, for example, overexpression of the tph (terephthalate degradation) gene cluster, which encodes enzymes that convert TPA into protocatechuate, and the removal of metabolic bottlenecks to optimize carbon flux and maximize substrate-to-product conversion. Collectively, these coordinated innovations in enzyme engineering, metabolic pathway design, and cell surface architecture provide a robust foundation for the development of next-generation PET bio-recycling platforms.