Current State and Perspectives Related to the Polyethylene Terephthalate Hydrolases Available for Biorecycling

Polyethylene terephthalate (PET) hydrolase is a challenging target as PET is a commonly used plastic that is extremely resistant to enzymatic attack. Since the discovery of a PET hydrolase from Thermobifida fusca in 2005, novel PET hydrolases and their availability toward waste PET have been investigated. At present, at least four thermophilic cutinases are known as PET hydrolases that could be used for the management of amorphous PET waste, such as packaging materials. Heat-labile PETase from Ideonella sakaiensis and its homologues from mesophilic bacteria exist in the environment. However, PET can be efficiently hydrolyzed with thermophilic hydrolases. This Review focuses on the current state of PET hydrolases and the potential of their application. Contrary to an amorphous PET, the enzymatic hydrolysis of crystalline PET (particularly PET bottles) remains to be fully elucidated. It cannot be assured whether the biorecycling of general PET would be put into practice in the near future, but the plan is getting closer to the goal. PET hydrolases can be versatile polyesterases as they can hydrolyze not only PET but also other polyesters. Additionally, the thermostability of PET hydrolases is advantageous to their application in terms of reaction speed and durability.