Plastic and its use in every sphere of life has almost become synonymous to life and with best efforts from science and technology to develop biodegradable plastics and administrative controls still plastic use and thus generated plastic pollution is endangering the wellbeing of environment (air, land and water) and living beings. Plastic is generally composed to have various toxic pollutants with a potential to cause great harm to the air, water and land. In simple words, plastic pollution is said to happen when waste plastic gather in an area and begun to negatively impact the natural environment and create problems for plants, wildlife and even human population. Due to its useful characteristics (light weight, enough strength, cost effective), plastic has many valuable uses, and we have become addicted to single-use or disposable plastic – with severe environmental consequences. About one million plastic drinking bottles are purchased by the users on minute to minute basis whereas, up to 5 trillion single-use plastic bags are used worldwide every year. Overall, half of all plastic produced worldwide is designed for its single use and throw. Researchers estimate that more than 8.3 billion tonnes of plastic has been produced since the early 1950s and about 60% of that plastic has ended up in either a landfill or the natural environment. Today, about 300 million tons of plastic is being wasted every year which is nearly equivalent to the weight of the entire human population. So, at this rate, by 2050 there will be more plastic in the oceans than fish, and that’s assuming that the volume of waste won’t increase, but it most certainly will.
This plastic debris represents a chemical pollution in several ways as they contain compounds that can be chemically transferred to organisms during ingestion. Some of these molecules are potentially toxic and can accumulate in the body. Besides, plastic bags also affect the growth of crops, by hindering the process of photosynthesis in agricultural fields. The most direct effect of plastic pollution is its (plastic) final disposition in the sea which causes a significant mortality of marine mammals, turtles and birds. The other effect is its consumption by hungry animals on land which cause ingestion and infection, that concerns the entire food chain of the ecosystem. Because of the use of different chemical additives during plastic production, plastics have potentially harmful effects on human health also due to its growing use in eating wares and the exposure to toxic chemicals coming out of plastic can cause cancers, birth defects, impaired immunity and other health problems. Taking into consideration the seriousness of surmounting plastic pollution, the solutions to tackle plastic pollution can be divided into different categories like: development of bio-degradable plastics at par with existing plastics in terms of quality and cost, also to follow the life style based on three R’s (Reduce, Re-use and Recycle) related to plastic as well as developing environmental friendly methods to reuse and recycle the wasted plastics. Plastic recycling consists of collecting plastic waste and reprocessing it into new products, to reduce the amount of plastic in the waste stream but the methods or techniques prevalent at present are again a source to new form of environmental pollution. Therefore, the best biodegradation of the wasted plastics is the use of bacteria to recycle the plastics into nature by converting them into biomaterial.
In this regard, scientists are trying to come up with novel solutions to remedy the plastic pollution crisis, and they’re thinking small – in a good way- a new enzyme capable of breaking down plastic bottles. This providential development could finally allow to fully recycle waste plastic in an environmental friendly manner. Recently, discovered Ideonella sakaiensis bacterium is called as plastic eating bacteria, however, it is far from the first living species to possess plastic eating proclivities as waxworm caterpillars have been found before to break down plastic in a matter of hours as well as the mealworms also possess gut microbes that eat through polystyrene. It is true that research in this direction is gain ground and it is likely that different microbes are evolving faster and better strategies to break down man-made plastics. It seems that nature is evolving solutions. Scientists in the beginning started with tests to see how the Ideonella sakaiensis bacterium managed to produce an enzyme capable of degrading PET, however, it turned out that inadvertently made enzyme, PETase, proved even better at degrading PET. The resulting mutant PETase takes just a few days to break down PET in comparison to the time of 450 years taken by plastics to degrade naturally. The salient feature in the use of PETase is to break down bottles before they end up in the environment. However, the enzyme could also augment plastics recycling approaches themselves.
The improvements to the PETase activity so far have not been dramatic, and we are nowhere near to a solution to plastic crisis but this research will definitely help scientists to understand how this promising enzyme breaks down PET and further they will understand how to they could make it work faster by manipulating its active parts. It is fairly unusual to be able to engineer enzymes to work better than they have evolved through nature. But, scientists can think of engineered enzymes which can break PET down to its building blocks which will enable the ability to do full bottle-to-bottle recycling. This could give scientists an exciting opportunity to overtake evolution by engineering optimized forms of PETase. After characterizing the structure of the enzyme by bludgeoning it with x-rays from the UK’s Diamond Light Source, which can hit objects with beams 10 billion times brighter than the Sun and helping scientists to distinguish individual atoms from one another. The research team changed the structure of PETase slightly in order to compare it with another enzyme which can break down cutin (a polymer found in the protective coating in plants). The process conferred PETase with a 20-percent improvement in degrading PET. This much improvement though is not exactly a radical shift from the original but it does promise the potential to go further and turn the enzyme into something with real, significant applications. Scientists hope of making the enzyme stable and active at temperatures above 158 degrees Fahrenheit, where PET becomes rubbery and breaks down 10 to 100 times faster. On the negative side of research, we can say that while any modified bacteria used in bioreactors are likely to be highly controlled, the fact that it evolved to degrade and consume plastic in the first place suggests this material we rely on so heavily may not be as durable as we thought. Further, if more bacteria began eating plastic in the wild, then products and structures of plastics designed to last many years could come under threat and the plastics industry would face the serious challenge of preventing its products becoming contaminated with hungry micro-organisms.
Further reading:
- https://theconversation.com/how-plastic-eating-bacteria-actually-work-a-chemist-explains-95233
- https://medium.com/swlh/plastic-eating-bacteria-9a26e1e7f9c5
- https://www.dtu.dk/english/news/2019/09/eng-bakterier-har-faaet-appetit-paa-plast?id=afa835a7-eb08-4f05-a5ee-9212464dcf26
- https://www.edf.org/blog/2018/07/13/are-plastic-eating-bacteria-solution-ocean-pollution-its-not-simple-science-shows
- https://abordonseng.wordpress.com/2018/12/25/plastic-eating-bacteria/
- Austin HP et al (2018)Characterization and engineering of a plastic-degrading aromatic polyesterase. Proc Nat Acad Sci 115, 19, E4350-E4357
- Brandon AM et al (2018)Biodegradation of Polyethylene and Plastic Mixtures in Mealworms (Larvae of Tenebrio molitor) and Effects on the Gut Microbiome. Environ Sci Technol 52, 6526-6533
- Griggs MB (2017 april 24)These caterpillars chow down on plastic bags. Popular Science. http://www.popsci.com
- Howard GT (2002)Biodegradation of polyurethane: a review. Int Biodeterior Biodegrad 42, 213-220
- https://en.wikipedia.org/wiki/Great_Pacific_garbage_patch
- https://en.wikipedia.org/wiki/PET_bottle_recycling
- https://en.wikipedia.org/wiki/Polyethylene_terephthalate
- Patel NV (2018 april 17)Scientists stumbled upon a plastic-eating bacterium – then accidentally made it stronger. Popular Science. http://www.popsci.com
- Russell JR et al (2011)Biodegradation of polyester polyurethane by endophytic fungi. Appl Environ Microbiol 77, 17, 6076-6084
- Sampedro J (2016 marzo 10)Descubierta una bacteria capaz de comerse un plástico muy común. El País
- Shah AA et al (2008)Biological degradation of plastics: a comprehensive review. Biotechnol Adv 26, 246-265
- Tanasupawat et al (2016)Ideonella sakaiensis nov., isolated from a microbial consortium that degrades poly(ethylene terephtalate). Int J Syst Evol Microbiol 66, 2813-2818
- Yang et al (2015)Biodegradation and mineralization of polystyrene by plastic-eating mealworms: Part 2. Role of gut microorganisms. Environ Sci Technol 49, 12087-12093
- Yoshida et al (2016)A bacterium that degrades and assimilates poly(ethylene terephthalate). Science 351,1196–1199
- https://neo.life/2019/12/plastic-eating-microbes-to-the-rescue/
- https://www.polymersolutions.com/blog/plastic-eating-bacteria-help-solve-plastic-disposal-problems/
- https://www.fastcompany.com/90412215/could-this-plastic-eating-enzyme-be-the-miracle-solution-to-our-plastic-problem
