Spider silk protein generates significant development interest due to its unique combination of properties, including high toughness and strength, extensibility, biocompatibility, thermal stability and others. Researchers at Rensselaer Polytechnic Institute (RPI; Troy, N.Y.; ) have developed what is said to be the first microbial platform to convert hydrocarbons derived from waste polyethylene (PE) into a silk protein similar to spider dragline spidroin, a complex biopolymer that has potential uses in coatings, packaging, fibers and sustainability applications. “Spider silk is nature’s Kevlar,” says Helen Zha, an assistant professor of chemical and biological engineering and one of the RPI 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, nontoxic and biodegradable.”

The RPI team used synthetic biology tools to engineer a new strain of Pseudomonas aeruginosa that contains genomically integrated recombinant genes for “spider dragline-inspired silk protein,” a biopolymer with the desired properties. The RPI team, collaborating with colleagues at Argonne National Laboratory (Lemont, Ill., ), subsequently demonstrated that the bacteria could convert plastic-derived substrates to protein-based materials. The polymer was “pre-digested” into smaller segments to allow the bacteria to ferment the material.

Non-biological methods for upcycling polyethylene, such as catalytic depolymerization and pyrolysis, are energy intensive and limited in the products they can generate, the researchers explain. The current study points the way to utilizing waste polyethylene to make a highly valuable biomaterial. The researchers are now working to optimize the recombinant gene in the bacteria to increase efficiency and decrease costs of the system.