Environmental Implications of Plastic-degrading Bacterial Enzymes in Polyethylene Terephthalate Bioremediation

Abstract

Polyethylene terephthalate (PET) is one of the most persistent synthetic polymers found in terrestrial and aquatic environments, and is responsible for long-term plastic accumulation and the formation of microplastic. Traditional mechanical and chemical recycling methods are still limited by contamination, degradation of polymer quality, energy consumption, and only suitable for concentrated waste streams. This review discusses and summarizes the available peer-reviewed data regarding the bacterial enzymes that degrade polyethylene terephthalate (PETase, MHETase, cutinases, and engineered variants of hydrolases). The literature was searched for the polyethyleneterephthalate biodegradation, bacterial enzymes, PETase, MHETase, plastisphere microorganisms, enzymatic recycling, environmental risk and bioremediation using major scientific databases such as PubMed, Scopus, Web of Science, ScienceDirect and Google Scholar. Only studies that focused on bacterial sources and isolation, enzymatic mechanisms, protein engineering, environmental effects, or scalability of polyethylene terephthalate degradation were included. Overall, there were 34 articles included in the final synthesis. The results indicate that bacterial enzymes can depolymerise PET to recoverable intermediates and monomers, although the practical use of these enzymes requires consideration of the crystallinity of the substrate, their catalytic efficiency under ambient conditions, enzyme instability and lack of knowledge of intermediates involved in natural ecosystems. There is current evidence that contained industrial enzymatic recycling is the most advanced near-term application, whereas open-environment bioremediation needs a more robust ecological risk assessment, standardised tests, and regulation. The production of environmentally robust enzyme variants, microbial consortia, life-cycle assessment, and safety frameworks for responsible deployment are promising areas for future research.