Various kinds of plastics have been developed over the past century, vastly improving the quality of life. However, the indiscriminate production and irresponsible management of plastics have led to the accumulation of plastic waste, emerging as a pressing environmental concern. To establish a clean and sustainable plastic economy, plastic recycling becomes imperative to mitigate resource depletion and replace non-eco-friendly processes, such as incineration. Although chemical and mechanical recycling technologies exist, the prevalence of composite plastics in product manufacturing complicates recycling efforts. In recent years, the biodegradation of plastics using enzymes and microorganisms has been reported, opening a new possibility for biotechnological plastic degradation and bio-upcycling. This review provides an overview of microbial strains capable of degrading various plastics, highlighting key enzymes and their role. In addition, recent advances in plastic waste valorization technology based on systems metabolic engineering are explored in detail. Finally, future perspectives on systems metabolic engineering strategies to develop a circular plastic bioeconomy are discussed.

Polyethylene (PE) exhibits high resistance to degradation, contributing to plastic pollution. PE discarded into the environment is photo-oxidized by sunlight and oxygen. In this study, a key enzyme capable of degrading oxidized PE is reported for the first time. Twenty different enzymes from various lipase families were evaluated for hydrolytic activity using substrates mimicking oxidized PE. Among them, Pelosinus fermentans lipase 1 (PFL1) specifically cleaved the ester bonds within the oxidized carbon-carbon backbone. Moreover, PFL1 (6 μM) degraded oxidized PE film, reducing the weight average and number average molecular weights by 44.6 and 11.3 %, respectively, within five days. Finally, structural analysis and molecular docking simulations were performed to elucidate the degradation mechanism of PFL1. The oxidized PE-degrading enzyme reported here will provide the groundwork for advancing PE waste treatment technology and for engineering microbes to repurpose PE waste into valuable chemicals.

Para-Coumaric acid (pCA), a naturally occurring phenolic compound found in various edible plants, holds significant potential in pharmaceutical development due to its diverse biological activities and its role as a key intermediate in the biosynthesis of pharmacologically important secondary metabolites. However, conventional extraction from plant sources is inefficient and poses concerns regarding food security. Moreover, recent global shortages of pharmaceutical ingredients have emphasized the urgent need for sustainable and reliable alternative production methods. In this study, an engineered Corynebacterium glutamicum strain was developed as a microbial cell factory for the sustainable biosynthesis of pCA. An ethanosolv fractionation process was integrated to utilize the carbohydrate fraction of Quercus mongolica lignocellulosic biomass for microbial fermentation, while the lignin fraction remains available for high-value applications. Using this integrated approach, 18.92 g/L of pCA was produced, with a yield of 0.49 Cmol/Cmol and a productivity of 0.24 g/L/h. This represents the highest pCA production reported to date and the first demonstration of pCA biosynthesis from lignocellulosic biomass. This work lays the foundation for the development of bioprocesses enabling the complete utilization of lignocellulosic feedstock and the sustainable production of valuable secondary metabolites.