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Using Bacterial Enzymes to Degrade Plasticizers
Context:
The rising levels of carcinogenic plasticizers in the environment, alongside plastics, pose a severe threat to human health.
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- Plasticizers are added to plastics and personal care products to enhance flexibility and shine and are commonly found in baby toys, shampoos, soaps, and food containers.
- These chemicals can be absorbed through the skin, making them a direct health hazard.
- Addressing this challenge, a team of researchers at IIT Roorkee has achieved a significant breakthrough by using an esterase enzyme from soil bacteria to degrade a particularly harmful plasticizer—diethyl hexyl phthalate (DEHP).
A Novel Application of Esterase Enzyme
- The research team successfully utilised an esterase enzyme produced by Sulfobacillus acidophilus bacteria to break down high molecular weight phthalate plasticizers like DEHP.
- Unlike previous studies that characterised this enzyme’s ability to degrade low molecular weight phthalate diesters, the IIT Roorkee researchers demonstrated its potential in degrading more complex and challenging plasticizers.
- The esterase enzyme was structurally characterised using X-ray crystallography, allowing researchers to identify its active sites and understand the detailed mechanism of DEHP degradation.
Efficient and Scalable Degradation
- The enzyme remains active for about a month and catalyses the breakdown of DEHP into mono-(2-ethylhexyl) phthalate (MEHP) and 2-ethyl hexanol.
- To facilitate large-scale applications, the researchers cloned the enzyme’s genes into E. coli bacteria, enabling mass production through aerobic culture.
- Furthermore, the enzyme shows potential for binding with molecules similar to polypropylene, offering a promising tool for removing polypropylene from contaminated water sources.
Comprehensive Biodegradation Approach
- In a groundbreaking sequence of steps, the researchers combined the esterase enzyme with enzymes from another soil bacterium, Comamonas testosteroni, to achieve complete degradation of DEHP into carbon dioxide and water. The process involves:
- Esterase enzyme: Breaking DEHP into MEHP and 2-ethyl hexanol.
- Subsequent enzymes: Degrading MEHP to phthalate, converting phthalate to intermediate compounds, and eventually transforming these intermediates into protocatechuate.
- Final stage: Using the bacteria’s tricarboxylic acid cycle to convert protocatechuate into carbon dioxide and water.
