Ideonella sakaiensis is the first bacterium known to consume plastic, specifically polyethylene terephthalate (PET). Over 300 million tons of plastic are produced annually, with 8 million tons entering oceans.
About Ideonella sakaiensis
Ideonella sakaiensis naturally inhabits soil and sediment contaminated with plastic. It uses polyethylene terephthalate (PET) as a source of carbon and energy.
Gram-negative Structure: It has a thin peptidoglycan layer and outer membrane.
Motility: Each cell is motile and has a single flagellum to aid movement.
Rod-Shaped Appearance: The typical shape optimizes adaptability in various environments.
Mesophilic Preferences: It thrives at temperatures between 25 to 37 degrees Celsius, similar to many living organisms.
Aerobic: Ideonella sakaiensis survives in environments with available oxygen.
The bacterium is first identified in plastic waste at a recycling center in Japan. It's isolated from a group of microorganisms found in the sediment sample, which also contains protozoa and yeast-like cells.
After PET is degraded by I. sakaiensis, the other microbes convert 75% of degraded PET into carbon dioxide (CO2). In a perfect world plants turn CO2 to oxygen through photosynthesis.
Carbon dioxide has many other uses, including in food and beverages, fire safety, manufacturing, and agriculture. It makes fizz in beer as a byproduct of yeast fermentation, powers fire extinguishers and inflates life rafts. Excess carbon dioxide contributes to greenhouse gases.
Ideonella sakaiensis has adapted over time to survive on synthetic material. PET is patented in the 1940s and becomes popular in the 70s. The bacteria evolve in response to the abundance in their environment.
Bacteria are natural decomposers and can consume such ingredients as toxic waste, heavy metals and rocks. If they can't eat it they adapt. They reproduce by binary fission, enabling speedy metabolic adjustments.
Exact timeline of evolution is unknown. Its fairly recent discovery suggests Ideonella sakaiensis adapts to a plastic diet decades before being found. Many microbes are genetically modified. This bacterium is all natural, but that is quickly changing.
How Ideonella sakaiensis Consumes PET
Ideonella sakaiensis attaches to the plastic surface with its flagellum. It produces two enzymes:
PETase (PET hydrolase): This enzyme breaks down long chains of PET molecules to the chemical mono(2-hydroxyethyl)terephthalic acid (MHET).
MHETase (MHET hydrolase): This enzyme further breaks down MHET into its constituent building blocks, terephthalic acid (TPA) and ethylene glycol.
These end products, TPA and ethylene glycol, are then metabolized by the bacteria for energy and growth.
Pros of Bacterial Plastic Remediation
Potential for Complete Degradation: Unlike mechanical recycling, which often degrades the quality of the plastic, Ideonella sakaiensis can theoretically break down PET into its constituent monomers.
Cost-Effective: Bioremediation using bacteria is hoped to be a more cost-effective alternative to traditional plastic recycling methods.
Environmentally Friendly: By breaking down plastic waste, bioremediation of plastics expects to reduce pollution and conserve resources.
Cons of Bacterial Plastic Remediation
Slow Degradation Rate: The natural degradation rate of PET by Ideonella sakaiensis is slow, making it impractical for large-scale waste management. It can take weeks to months to fully degrade a small piece of plastic.
Environmental Factors: The efficiency of the bacteria can be influenced by environmental factors, such as temperature, pH, and the presence of contaminants destructive to its existence.
Enzyme Optimization: Further research is needed to optimize the activity of PETase and MHETase to improve their efficiency.
Plastic Specificity: I. sakaiensis primarily targets PET, which limits applications in addressing countless other types of plastics.
Current Use and Future Prospects
Almost ten years after its discovery, Ideonella sakaiensis is not being used on a large scale to bioremediate polluted areas. The primary focus is on research and development.
Scientists hope to achieve:
Enzyme Engineering: Modifying the PETase and MHETase enzymes to enhance their activity, making them more efficient at decomposing PET.
Scientists have already managed to increase efficiency of PETase through protein engineering. They've created a "super-enzyme" to break down PET faster than the naturally occurring enzyme.
Scale-up Strategies: Trying to figure out how to cultivate the bacteria on a large scale and implement bioremediation strategies in real-world settings instead of plastic pipe dreams.
The Global Plastic Problem
Every year, around 300 million tons of plastic waste ends up in landfills and oceans, where it can persist for hundreds of years. This persistent pollution endangers marine life and brings microplastics into the food chain.
In 2018 China stops accepting recycling. This causes a huge backlog as systems scramble to send recycling to Vietnam, Malaysia and Indonesia. Poorly equipped to handle it, many countries dump overflow into landfills.
Some estimates suggest by 2050 the weight of plastic in the oceans could exceed that of all fish combined. For instance the Great Pacific Garbage Patch is an accumulation of marine debris in the North Pacific Ocean.
Referred to as the Pacific trash vortex, it consists of two separate collections of debris encircled by the vast North Pacific Subtropical Gyre. It's estimated to be 1.6 million sq km, three times the size of France.
Persistence: Plastics are incredibly durable and can persist in the environment for hundreds, even thousands, of years.
Ubiquitous Presence: Plastic debris contaminates virtually every corner of the Earth, from the deepest ocean trenches to the highest mountain peaks.
Ecological Damage: Plastic pollution harms wildlife through entanglement, ingestion, and habitat destruction. Microplastics, tiny plastic particles, can also accumulate in the food chain, posing potential health risks.
Landfill Overflow: The sheer volume of plastic waste overwhelms landfills, contributing to land degradation and greenhouse gas emissions.
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