Biodegradation of PET: Current Status and Application Aspects

Abstract

Most petroleum-derived plastics, as exemplified by poly­(ethylene terephthalate) (PET), are chemically inactive and highly resistant to microbial attack. The accumulation of plastic waste results in environmental pollution and threatens ecosystems, referred to as the “microplastic issue”. Recently, PET hydrolytic enzymes (PHEs) have been identified and we reported PET degradation by a microbial consortium and its bacterial resident, Ideonella sakaiensis. Bioremediation may thus provide an alternative solution to recycling plastic waste. The mechanism of PET degradation into benign monomers by PET hydrolase and mono­(2-hydroxyethyl) terephthalic acid (MHET) hydrolase from I. sakaiensis has been elucidated; nevertheless, biodegradation may require additional development for commercialization owing to the low catalytic activity of these enzymes. Here, we introduce PET degrading microorganisms and the enzymes involved, along with the evolution of PHEs to address the issues that hamper microbial and enzymatic PET degradation. Potential applications of PET degradation are also discussed.

Biodegradation of waste PET

“…PETase and MHETase catalyze similar reactions in different locations. Extracellular PETase hydrolyzes PET into MHET, which is transported into the periplasmic space of I. sakaiensis where outer membrane‐anchored MHETase hydrolyzes MHET into TPA and EG . This combination and arrangement of enzymes for metabolizing PET has so far not been found in any other organisms with fully sequenced genomes.…”

“…Phylogenetic tree analysis of PHEs shows that these enzymes appear in both eukaryotes and bacteria . The bacterial domain that expresses PHEs is further divided into two major branches belonging to the phyla Actinobacteria and Proteobacteria .…”

“…We think that further biodegradation of PET can become an important innovative technology for a circular economy in the near future and for meeting Sustainable Development Goals. Ideonella sakaiensis and other organisms and their hydrolyzing enzymes would be central for developing various potential applications (Fig ) .…”

Microbial Degradation and Valorization of Plastic Wastes

“…In recent years, a number of studies have reported that several microorganisms and enzymes are capable of degrading synthetic plastics. Although numerous reviews and viewpoints on the topic of biodegradation of plastic have been published, they have mainly focused on the biodegradation of a single kind of plastic, such as PE (Restrepo-Flórez et al, 2014), PS (Ho et al, 2018), PP (Arutchelvi et al, 2008), PUR (Cregut et al, 2013;Peng et al, 2018;Magnin et al, 2019c), and PET (Wei and Zimmermann, 2017a;Kawai et al, 2019;Taniguchi et al, 2019). A comprehensive review into biodegradation of all main kinds of plastic is necessary (Wei and Zimmermann, 2017b).…”

Computational redesign of a PETase for plastic biodegradation by the GRAPE strategy

“…Not content with the finite repertoire of naturally occurring enzymes, numerous research groups have concerned on the engineering of IsPETase, which has been summarized by Taniguchi recently 14 . Recently crystal structures of PET degrading enzymes allow for expedients that exploit rational design to improve the PET degradation activity [15][16][17][18][19][20][21] .…”