Today, plastic materials are used in almost every area of our daily lives. This usage results in approximately 400 million tons of plastic waste each year. Only 20% of these 400 million tons of plastic waste is recycled. As we all know, plastics can remain in the environment for a long time. This is because they are extremely resistant to nature (Guo et al., 2024).
Among various types of plastic, polyethylene terephthalate (PET) is widely used in beverage bottles, food packaging, and textile products due to its low cost and durability. This durable plastic is highly resistant to natural decomposition. This is why PET accumulations occur in terrestrial and marine ecosystems. PETs that are attempted to be recycled using mechanical and chemical recycling methods can cause even more damage to the environment at this stage. Secondary pollutants formed during recycling can mix into the environment and pose even greater threats. In addition, a significant amount of energy is used in this type of recycling. For this reason, scientists have recently begun using a method called enzymatic recycling. This approach, which is a promising alternative for PET waste management, offers an environmentally friendly solution for recycling plastic waste(Guo et al., 2024).
If you’d like, let’s take a closer look at the details of this eco-friendly recycling process together.
PETase was first identified in the bacterium Ideonellasakaiensis. This bacterium was isolated from a plastic waste recycling facility. The significance of this bacterium is that it uses PET as a carbon and energy source and represents the first characterized biological PET degradation system (Satta et al., 2024).
Plastics known as PET are formed from repeating units such as terephthalic acid (TPA) and ethylene glycol (EG) through the bonding of ester bonds. These plastics form a highly crystalline and hydrophobic polymer matrix. This structural arrangement limits enzyme accessibility. This has led to the assumption that PET is biologically inert. This assumption was refined with the discovery of enzymes that break down PET. These enzymes, called PETases, break the ester bonds in the polymer structure and catalyze the hydrolysis of PET. The primary intermediate produced as a result of primary degradation is called mono-(2-hydroxyethyl) terephthalate (MHET). Subsequently, an enzyme called MHETasecompletes the depolymerization process by hydrolyzing the primary intermediate MHET into its monomeric components, TPA and EG (Ermis, 2025). These monomers can be reused later (Guo et al., 2024).
In addition to PETases and MHETases, enzyme groups called cutinases have also shown PET degradation activity. However, research has focused on PETases because they exhibit higher substrate specificity and structural applicability for engineering purposes. (Guo et al., 2024).
Although PETase enzymes are environmentally friendly and effective, wild-type PETases do not possess such an effective catalytic effect. For this reason, protein engineering methods are frequently used. By modifying the amino acid residues near the active site of wild-type PETases, the substrate binding and catalytic conversion of these enzymes are improved(Sherigar et al., 2025).
One of the important studies conducted in this field focused on the degradation of strong PET found in carbonated beverage bottles using PETase enzymes engineered through specialized methods. In this study, S238Y was selected as the most successful mutant PETase enzyme. This enzyme was developed using computer-aided modeling and docking methods. The wild-type PETase enzyme and the mutant S238Y enzyme were compared. As a result, the mutant enzyme showed 3.3 times more degradation activity. This important study shows us that a single amino acid sequence change can make enzymes much more aggressive against PET bottles (Sevilla et al., 2023).
These structural mutations also provide enzymes with flexibility and high surface interaction. Therefore, PET degradation rates are more frequently observed in interactions with mutated enzymes (Tadokoro & Imai, 2025).
Today, enzymatic PET degradation studies are often performed in laboratory settings. Recently, these laboratory studies have begun to be transferred to pilot-scale industrial applications. A key strategy is the development of whole-cell biocatalysts through the engineering of microorganisms containing PETase and MHETase on their cell surfaces. This simplifies enzyme recovery and increases its stability. Thanks to this strategy, it enhances the reusability of enzymes in PET recycling (Jiang et al., 2025).
Enzymatic recycling is important not only for PET but also for the recycling of other microplastics. They hold great promise for eliminating microplastic pollution. Engineered PETase variants play an active role in various wastewater treatment and environmental improvement applications because they are effective against PET microfibers (Zurier & Goddard, 2023).
As a result, this enzymatic PET recycling aims to significantly reduce plastic waste in an environmentally friendly manner. Following the discovery of PETases, advanced engineering has enabled the degradation of these supposedly indestructible synthetic polymers, even converting them into reusable monomers (Satta et al., 2024).
In the future, the discovery of newer and more effective plastic-degrading enzymes will increase the use of this effective method, which will be crucial for both the environment and human health. While enzymatic recycling alone cannot solve the global plastic problem, it plays an important role in achieving a sustainable environment and a circular plastic economy.
References:
https://doi.org/10.1007/s10311-024-01714-6
https://doi.org/10.1101/2025.03.24.645130
https://doi.org/10.1021/acsestwater.3c00021
Denetmen: Emine ARSLAN
