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Developed by researchers at Rensselaer Polytechnic Institute (RPI) in New York, the engineered Pseudomonas aeruginosa turned polyethylene – found in many single-use items – into a high-value protein.
That product, which the researchers call ‘bio-inspired spider silk’ because of its similarity to the natural material, could have applications in textiles, cosmetics, and even medicine.
“Spider silk is nature’s Kevlar,” said Helen Zha, one of the researchers leading the project. “It can be nearly as strong as steel under tension. However, it’s six-times less dense than steel, so it’s very lightweight. As a bioplastic, it’s stretchy, tough, non-toxic, and biodegradable.”
Polyethylene, found in products such as plastic bags, water bottles, and food packaging, is the biggest contributor to plastic pollution globally and can take more than 1,000 years to degrade naturally. Only a small portion is recycled, so the bacteria used in the study could help ‘upcycle’ some of the remaining waste.
Pseudomonas aeruginosa can naturally consume polyethylene as a food source. After engineering the bacteria to convert the carbon atoms of polyethylene into a genetically encoded silk protein, the RPI team found that it produced yields rivalling some strains that are conventionally used in biomanufacturing.
The plastic is first ‘predigested’ so the bacteria can consume it. It is then depolymerised by being heated under pressure, producing a soft, waxy substance. Next, the team put a layer of the plastic-derived wax on the bottoms of flasks, which serve as the nutrient source for the bacteria culture. The bacteria then ferment the material.
After 72 hours, the scientists strain out the bacteria from the liquid culture, purify the silk protein, and freeze-dry it. At that stage, the protein, which the researchers said looks like “torn up cotton balls”, could potentially be spun into thread or made into other useful forms.
“What’s really exciting about this process is that, unlike the way plastics are produced today, our process is low energy and doesn’t require the use of toxic chemicals,” Zha said. “The best chemists in the world could not convert polyethylene into spider silk, but these bacteria can. We’re really harnessing what nature has developed.”
Before upcycled spider silk products become a reality, the researchers first need to improve the efficiency of the process.
“This study establishes that we can use these bacteria to convert plastic to spider silk. Our future work will investigate whether tweaking the bacteria or other aspects of the process will allow us to scale up production,” said Mattheos Koffas, another researcher leading the project.
The work was published in Microbial Cell Factories.
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