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.
Highlights
Worldwide plastic production reached 348 million metric tons in 2017, and this number increases annually by ∼5% (PlasticEurope, 2019; Brahney et al, 2020)
The activity towards polyethylene terephthalate (PET) film as a substrate increased by 22.4% in 18 h and 32.4% in 36 h in terephthalic acid (TPA) and mono-2-hydroxyethyl terephthalate (MHET) release in comparison to IsPETaseW/T
The results suggested that PETase is not fully optimized for crystalline PET degradation (Austin et al, 2018)
Summary
Worldwide plastic production reached 348 million metric tons in 2017, and this number increases annually by ∼5% (PlasticEurope, 2019; Brahney et al, 2020). Predictions about plastic waste accumulation in ecosystems suggest that in 2050 cumulative plastic waste production will reach over 25 billion tonnes, i.e., 3 times the current level (Geyer et al, 2017). It is estimated that more than 800 animal species are affected by plastic waste, and around 90% of all seabirds ingest plastic (Wilcox et al, 2015). Both nanoplastics and microplastics were found in zooplankton and phytoplankton (Rummel et al, 2017), which are consumed by organisms from higher levels of the food chain. It was shown that nanoplastics may reduce the survival of aquatic zooplankton and penetrate the blood-brain barrier in fish and cause behavioural disorders
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