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Bioremediation could be an effective new tool for reducing PET microplastic pollution



Microplastics in aquatic environments are of increasing concern


Only a small portion of the huge amount of plastic produced in the world is recycled. Large

quantities of plastics contaminate the environment; in particular, microplastics, less than 5 mm in

diameter, consisting mainly of polystyrene (PS) or polyethylene terephthalate (PET), have a negative impact on the aquatic environment and health. In fact, growing concern is about possible risks to human health and toxicity to aquatic organisms from chronic exposure to microplastics.

Although PET is considered nontoxic, its microgranules are durable, ubiquitous in marine and

terrestrial habitats, and accumulate in living organisms. PET is characterized by remarkable chemical inertness, making it resistant to environmental degradation.


New perspectives for bioremediation of PET microplastics


Several enzymes capable of hydrolyzing PET into terephthalic acid (TPA) and ethylene glycol have

been identified, but at high temperatures and with low activity. Recently, the bacterial strain

Ideonella sakaiensis 201-F6 was observed to be able to grow on PET films with low crystallinity.

Two α/β-hydrolase enzymes of I. sakaiensis are able to degrade PET in two steps: the PETase

converts PET to mono-(2-hydroxyethyl) terephthalate (MHET) and MHETase hydrolyzes MHET to

TPA and ethylene glycol.


The PETase of I. sakaiensis is active at room temperature. Recent crystal structures of the ligand-

bound PETase confirmed the predicted α/β-hydrolytic folding, which is typical of many other plastic-degrading enzymes known to date. In addition, the binding of PETase to the substrate and

the mode of catalysis were elucidated.

Based on phylogenetic analysis, MHETase from I. sakaiensis, the second key enzyme for complete


PET degradation, is part of the subfamily of tannase enzymes within the broader family of α/β-

hydrolase enzymes. MHETase has been shown to exclusively hydrolyze MHET, but not other compounds that are converted by other tannase family enzymes, indicating a very narrow substrate

specificity. The identification of the structure of MHETase represents a key step in understanding

the microbial process of PET degradation in I. sakaiensis.


Scientific research on novel bioremediation systems, based on new enzymes, in silico analysis and

optimization of microbiological systems, is a priority in Aspidia's scientific research activities. Our

goal is to help create a cleaner, healthier and friendlier world.

That is why we ask all of you, investors and philanthropists who care about the health of the

environment, to support Aspidia's research projects with your contributions.


The Aspidia team


References


Palm GJ, Reisky L, Böttcher D, et al.

Structure of the plastic-degrading Ideonella sakaiensis MHETase bound to a substrate. Nat Commun. 2019;10(1):1717. doi:10.1038/s41467-019-09326-3.

Piccardo M, Provenza F, Grazioli E, Cavallo A, Terlizzi A, Renzi M.

PET microplastics toxicity on marine key species is influenced by pH, particle size and food variations. Sci Total Environ. 2020;715:136947. doi:10.1016/j.scitotenv.2020.136947.

Tamargo A, Molinero N, Reinosa JJ, et al.

PET microplastics affect human gut microbiota communities during simulated gastrointestinal digestion, first evidence of plausible polymer biodegradation during human digestion. Sci Rep. 2022;12(1):528. doi:10.1038/s41598-021-04489-w.

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