Current Knowledge on Polyethylene Terephthalate Degradation by Genetically Modified Microorganisms

Abstract

The global production of polyethylene terephthalate (PET) is estimated to reach 87.16 million metric tons by 2022. After a single use, a remarkable part of PET is accumulated in the natural environment as plastic waste. Due to high hydrophobicity and high molecular weight, PET is hardly biodegraded by wild-type microorganisms. To solve the global problem of uncontrolled pollution by PET, the degradation of plastic by genetically modified microorganisms has become a promising alternative for the plastic circular economy. In recent years many studies have been conducted to improve the microbial capacity for PET degradation. In this review, we summarize the current knowledge about metabolic engineering of microorganisms and protein engineering for increased biodegradation of PET. The focus is on mutations introduced to the enzymes of the hydrolase class—PETase, MHETase and cutinase—which in the last few years have attracted growing interest for the PET degradation processes. The modifications described in this work summarize the results obtained so far on the hydrolysis of polyethylene terephthalate based on the released degradation products of this polymer.

An Overview into Polyethylene Terephthalate (PET) Hydrolases and Efforts in Tailoring Enzymes for Improved Plastic Degradation

“…It is noteworthy to mention here that enzymatic recycling offers a greener avenue to depolymerizing and recycling PET waste [ 8 , 81 ]. This is because enzymatic PET recycling offers several benefits over chemical depolymerization.…”

“…Conversely, CALB could transform MHET into TPA but exhibited a lower efficiency when used alone to hydrolyze PET [ 74 ]. The two lipases were seen to work synergistically to enhance PET hydrolysis following their complementary properties both in catalysis patterns and substrate specificity [ 8 , 143 ]. That said, the findings showed that the enzymes make ideal bioagents for the future biodegradation of plastics.…”

“…The global shift from reusable to single-use containers is also a causal factor in the rise of plastic usage in the packaging sector [ 1 ]. However, the robust properties of plastic, which were once thought to be an advantage, are now the root of the steady rise in plastic waste in terrestrial and marine environments [ 8 ]. Plastics are persistent materials, given that the construction of monomers from fossil fuel-derived hydrocarbons takes up to ~1000 years to decompose naturally, thus accumulating in the environment [ 9 ].…”

“…Its noteworthy uses include disposable plastic bottles, food jars, and plastic film. PET production increased to 33 million metric tons in 2015 (Geyer et al, 2017) and currently represents 80% of total global plastic usage [ 8 ]. The persistence of PET waste in terrestrial and marine environments could harm or kill some organisms, as only a very low portion of this plastic is recycled to recover its original forms, such as TPA and EG [ 8 , 36 ].…”

“…PET production increased to 33 million metric tons in 2015 (Geyer et al, 2017) and currently represents 80% of total global plastic usage [ 8 ]. The persistence of PET waste in terrestrial and marine environments could harm or kill some organisms, as only a very low portion of this plastic is recycled to recover its original forms, such as TPA and EG [ 8 , 36 ]. Having said that, scientific research on PET should be geared toward sustainability by bioprospecting or developing more hydrolases that can cleave the ester linkages in the amorphous domain of PET to enable the bioremediation of PET [ 31 ], since various microorganisms naturally produce enzymes.…”