Why is it hard to degrade plastics by microorganisms?

Ideonella sakaiensis

Given all this, it is easy to understand the enormous interest in the discovery of an enzyme capable of digesting polyethylene terephthalate. And now the plastic degrading capacity of this enzyme, called PETase, has been increased. This novelty is described in an article published in Proceedings of the National Academy of Sciences of the United States of America (PNAS).

“Polyethylene terephthalate, used primarily in the manufacture of beverage bottles, is also widely used in the manufacture of clothing, carpets and other objects. In our research we characterized the three-dimensional structure of the enzyme capable of digesting this plastic, engineered it to increase its degradation power and demonstrated that it also has activity in polyethylene-2,5-furanodicarboxylate (PEF), a substitute for PET made from renewable raw materials,” said Silveira.

“Apart from identifying Ideonella sakaiensis, the Japanese discovered that Ideonella sakaiensis produced two enzymes that are secreted into the environment. One of the enzymes secreted was precisely PETase. Because it has a certain degree of crystallinity, PET is a polymer that is extremely difficult to degrade.

How plastic degrades

Following in the wake of this enzyme, scientists from different countries (United Kingdom, United States, Brazil and China, among others) are studying its structure in order to replicate its mechanisms. This is the case of an experiment carried out by researchers from the University of Portsmouth (UK) and the US Department of Energy, who have managed to optimize the decomposition of plastic (up to 10% faster) through a mutation of this enzyme. A further step would be to transplant this mutant enzyme into bacteria, capable of surviving temperatures of up to 70°C, when PET becomes viscous and dissolves faster.

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The revolutionary potential of these experiments lies in the fact that all living things contain enzymes that serve to accelerate chemical reactions that occur in their respective organisms, such as digesting food. Furthermore, the fact that the PETase enzyme can digest PET plastic is very relevant in environmental terms, since this type of plastic is one of the main sources of pollution.

Degradation of plastics by microorganisms

Two of the previous issues to take into account are the existence of a long list of plastics (high molecular weight organic polymers generally synthesized from petroleum derivatives), and characteristics shared by most of these materials such as difficult or no biodegradability (they do not decompose into their constituent chemical elements by the action of biological agents such as microorganisms, plants or animals).

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A study published this July by twelve researchers from Austria in the journal Frontiers in Bioengineering and Biotechnology brings a new dimension to this type of possible solutions to the problem of plastic waste.

Although the possible future application of this proposal opens many unknowns, this team led by Felice Quartinello, from the University of Natural Resources and Life Sciences in Vienna (Austria), has proven in the laboratory that the microbiome (set of microbes: bacteria, archaea, viruses, fungi and protists) naturally present in the rumen (one of the esophageal compartments of the digestive tract of ruminants) of cows grazing in alpine meadows is capable of degrading the three types of polyesters analyzed: PET (polyethylene terephthalate), PBAT (Poly(Butylene Adipate-co-Terephthalate) and PEF (Polyethylene Furanoate).

Degradation of plastics by microorganisms pdf

The first synthetic polymer was Bakelite, created by Belgian chemist Leo Hendrik Baekeland in 1909. Baekeland reacted phenol, formaldehyde and other ingredients under pressure and at high temperature. The resulting material was used primarily to make insulating parts for electrical equipment such as radios and telephones. From then on, the development of a huge number of different plastics began: vinyl, polystyrene, acrylic, polyurethane and many others. Each has taken its place in the industry and all have achieved great commercial success.

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Polyurethane items can be recycled, but this is generally secondary recycling, because the resulting material cannot be used to manufacture products with the same value as the original items. There are two recycling routes: mechanical and chemical. In mechanical recycling, polyurethane waste is crushed or pulverized for use in the production of new articles. In chemical recycling, on the other hand, the aim is to break down the material. There remains the problem of the safe handling of the waste, which is added to that of other plastics to reach the impressive figure of five million tons per year in the United States and Canada alone.