Recent advances in screening and identification of PET-degrading enzymes

Polyethylene terephthalate (PET) is widely used in plastic bottles, packaging, and textile fibers. However, PET is difficult to degrade in nature and rapidly accumulates into the environment, causing serious environmental pollution and threatening human health. At present, the recycling methods for PET mainly focus on physical recycling and chemical degradation, but these methods have severe limitations resulting in the great loss of valuable materials and secondary pollution. In contrast, the biodegradation of PET is gradually attracting attention because of its environmental friendliness, high efficiency, and cost-effectiveness. Several PET-degrading enzymes (PDEs) have been previously identified, such as cutinase, IsPETase, lipase, and esterase. Thereafter, many efforts have been made to push the boundaries of evolution schemes, attempting to create stronger PDEs with improved activity and stability. Nevertheless, most of these enzymes show preferences towards low-crystallinity (<10%) PET, while in situ enzymatic degradation of high-crystallinity PET (30%-50%) remains a major challenge. Exploring and engineering PDEs that can efficiently degrade bottle-grade PET plastics has become a research hotspot recently. This review systematically introduces the current advances in PDEs and emphasizes the role of metagenomics in screening and identifying new PDEs.