Maya Ellison
Plastic is a complex polymer that forms long, repeating chains of molecules that don't dissolve in water. This makes plastic very durable and difficult to decompose naturally. However, certain bacteria have been discovered to possess the ability to break down plastic, offering a potential solution to the global plastic crisis. Ideonella sakaiensis, for example, can break down the bonds between monomers using enzymes, converting plastic into basic nutrients. This discovery has spurred research into the development of super-enzymes that can break down plastic faster and more efficiently, with potential applications in recycling and bioremediation. While challenges remain, the ability of bacteria to break down plastic presents an exciting opportunity to address the pressing issue of plastic pollution.
| Characteristics | Values |
|---|---|
| Bacteria that breaks down plastic | Ideonella sakaiensis |
| Type of plastic it breaks down | Polyethylene terephthalate (PET) |
| How it breaks down plastic | Uses enzymes called PETase to break down PET into mono(2-hydroxyethyl)terephthalic acid (MHET) |
| How long it takes to break down plastic | The wild-type bacterium can break down a thin (0.2 mm thickness) film of low-crystallinity (soft) PET in approximately 6 weeks |
| Genetically modified? | Yes, in one instance, the PETase enzyme was genetically modified and combined with MHETase to break down PET faster |
| Other methods | Researchers have genetically engineered a marine microorganism to break down plastic in saltwater |
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What You'll Learn
The discovery of Ideonella sakaiensis
In 2016, a team of researchers led by Kohei Oda of the Kyoto Institute of Technology and Kenji Miyamoto of Keio University discovered a new bacterium, Ideonella sakaiensis, which is capable of breaking down and consuming polyethylene terephthalate (PET) plastic. Ideonella sakaiensis was first isolated from a sediment sample taken outside a plastic bottle recycling facility in Sakai City, Japan. The bacterium was named after the city of Sakai, where it was discovered.
The potential of Ideonella sakaiensis in plastic degradation was initially observed when Oda and his team discovered bacteria breaking down plastic in a rubbish dump. However, the preliminary findings were not published at the time as plastic pollution was not yet recognized as a critical issue. Years later, Oda and his student, Kazumi Hiraga, continued their research and experiments, eventually publishing their groundbreaking work in the journal Science in 2016.
Ideonella sakaiensis has also been studied for its potential in sewage-fed fisheries, where it has shown promise as a cost-effective anti-pollutant. Additionally, its ability to break down PET has inspired innovative concepts, such as the coagulation filtration system designed by fifth graders Julia Stewart and Jacob Park, showcasing the bacterium's versatility and potential for environmental applications.
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How bacteria break down plastic into nutrients
Plastic is a complex polymer, meaning it is made up of long, repeating chains of molecules that do not dissolve in water. This makes plastic very durable and means it takes a long time to decompose naturally. However, some bacteria have been discovered to break down plastic into nutrients.
In 2016, scientists from Japan tested different bacteria from a bottle recycling plant and discovered that a bacterium, Ideonella sakaiensis, could break down plastic. This bacterium was named after the city of Sakai, Japan, where it was discovered. Ideonella sakaiensis is a gram-negative, rod-shaped bacterium that has evolved to use plastic as a food source.
The bacterium breaks down the plastic by using enzymes, specifically a PET plastic-degrading enzyme known as PETase. This enzyme is tailored to bind to PET surfaces and works at temperatures above 30°C, making it suitable for recycling in bioreactors. Ideonella sakaiensis adheres to the PET surface and uses the PETase enzyme to degrade the PET into mono(2-hydroxyethyl)terephthalic acid (MHET). The PETase also degrades PET into another intermediate known as Bis-(2-hydroxyethyl) terephthalate (BHET), which can be further converted into MHET.
The resulting MHET is then degraded into its two monomeric constituents by an MHET hydrolase enzyme, or MHETase, on the cell's outer membrane. These monomeric constituents, such as ethylene glycol, are then taken up and used by the bacterium as nutrients. The bacterium takes what it needs and excretes the rest.
While the discovery of Ideonella sakaiensis and its ability to break down plastic is promising, there are still challenges to be addressed. The process of breaking down plastic using enzymes is generally slow, and making these processes faster and more efficient is a complex task. Additionally, the enzymes need to be in an environment with temperatures above 30°C, which is not naturally present in many parts of the world, adding to the cost and environmental impact of the process.
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Genetically modified bacteria
The discovery of plastic-eating bacteria has opened up new possibilities for addressing the global plastic crisis. Ideonella sakaiensis, a bacterium discovered in a rubbish dump in Japan, is capable of breaking down and consuming polyethylene terephthalate (PET), a common plastic used in packaging and bottles. This bacterium produces a specific enzyme, PETase, that enables it to break down PET into its precursor liquids.
While Ideonella sakaiensis represents a significant finding, researchers have also been exploring ways to genetically modify bacteria to enhance their plastic-degrading capabilities. One approach involves combining the PETase enzyme with another enzyme, MHETase, to break down PET faster and also target other types of plastics like PEF (polyethylene furanoate). This combination of enzymes has shown promise in recycling and upcycling mixed plastics.
Genetic engineering techniques have been employed to modify bacteria further. Researchers have worked with two species of bacteria: Vibrio natriegens, which thrives in saltwater and reproduces quickly, and Ideonella sakaiensis, which produces the PETase enzyme. By transferring the PETase-producing genes from I. sakaiensis into V. natriegens, scientists created a new organism capable of breaking down PET in a saltwater environment. This achievement is notable because saltwater environments are challenging for plastic degradation, and this development opens up new possibilities for addressing marine plastic pollution.
The process of genetically modifying these bacteria involves incorporating the genetic sequence for producing PETase into a plasmid, which can replicate independently within a cell. By introducing this plasmid into V. natriegens, the bacteria start producing the desired enzymes on their cell surfaces. This approach has been successful, and the modified V. natriegens bacteria can now break down PET in saltwater at room temperature.
While these developments are exciting, it's important to acknowledge that there are still challenges and limitations. The process of breaking down plastics with bacteria, whether naturally occurring or genetically modified, tends to be slow, and scaling up these processes to address global plastic waste remains a hurdle. Additionally, certain enzymes required for plastic degradation only function in specific temperature ranges, limiting their applicability in certain regions without incurring additional costs for heating.
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The role of enzymes
Enzymes are essential to the process of bacteria breaking down plastic. They are tiny molecular machines within a cell that are specialised to break down larger compounds. In the case of plastic degradation, enzymes work to break down the complex polymers that make up plastics into smaller, soluble chemical units.
The bacterium Ideonella sakaiensis, for example, produces an enzyme called PETase that breaks down PET plastics. PET plastics are made up of repeated units of C10H8O4, which are monomers that chemically react with other monomers to form long chains called polymers. The PETase enzyme works by hydrolyzing the ester bonds present in PET, breaking it down into intermediate compounds such as mono(2-hydroxyethyl)terephthalic acid (MHET) and Bis-(2-hydroxyethyl) terephthalate (BHET). These intermediates are further degraded into their monomeric constituents, such as terephthalic acid (TPA) and ethylene glycol, which can then be absorbed and used by the bacterium.
The discovery of Ideonella sakaiensis and its ability to break down PET plastics has spurred research into the potential of enzymes for plastic biodegradation and recycling. Scientists have been working to understand the structure and mechanisms of the PETase enzyme to engineer optimised forms that can break down plastics more efficiently. For example, researchers at the University of Portsmouth engineered PETase to break down bottles in days rather than months, and combined it with another enzyme to create a 'super-enzyme' that worked six times faster.
Additionally, enzymes have been identified in other bacteria that can break down plastics. For instance, a French firm has optimised an enzyme that depolymerises 97% of PET starting materials into monomers in just 24 hours. This enzyme has potential in recycling and upcycling mixed plastics.
While the use of enzymes to break down plastics is a promising approach, there are still challenges to be addressed. The physical properties of plastics make it difficult for enzymes to interact with them, and most reported cases of enzymes degrading plastic are slow and incomplete. Furthermore, the cost of heating the bacteria to the required temperature for enzyme activity can be prohibitive. However, with ongoing research and advancements, the use of enzymes in plastic biodegradation holds potential for addressing the global plastic crisis.
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The future of plastic-eating bacteria
Plastic-eating bacteria hold great potential for the future of waste management and recycling. The discovery of bacteria, such as Ideonella sakaiensis, that can naturally break down certain types of plastics, has sparked significant interest in the scientific community.
One of the key advantages of using bacteria to break down plastics is their ability to target specific types of plastics. For example, Ideonella sakaiensis produces an enzyme, PETase, that specifically breaks down polyethylene terephthalate (PET), a common plastic used in packaging and textiles. This specificity allows for more efficient recycling processes, as the enzyme can chemically sort out PET from mixed waste samples.
Additionally, the use of bacteria to break down plastics can reduce the need for mechanical or chemical processes, which often require additional energy and resources. By harnessing the power of enzymes, bacteria can naturally break down plastics into their precursor molecules, which can then be used to create new plastic products. This approach brings us closer to achieving truly recyclable plastics, similar to materials like glass or aluminum.
While the field of plastic-eating bacteria is still in its early stages, ongoing research and development are driving innovation. Scientists are working to improve the efficiency of these bacteria by engineering enzymes to break down plastics faster and work under a wider range of temperature conditions. For example, researchers have combined PETase with another enzyme to create a 'super-enzyme' that works six times faster.
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Frequently asked questions
Ideonella sakaiensis.
Ideonella sakaiensis uses enzymes to break down the bonds between monomers.
Polyethylene terephthalate (PET), the most common plastic found in clothing and packaging.
In lab conditions, Ideonella sakaiensis broke down a 2cm-long piece of plastic film in about seven weeks.
Ideonella sakaiensis has the potential to be used for the degradation of PET plastics and to create more environmentally friendly recycling processes.
