Novel genetically engineered silk materials for recycling polyethylene terephthalate (PET) plastic waste

Polyethylene terephthalate (PET) is a widely used plastic whose poor degradability has led to serious environmental pollution. In recent years, it was shown that the engineered enzyme FAST-PETase can efficiently catalyze the hydrolysis of PET into monomers; however, large-scale production and low-cost application of this enzyme remain challenging. In this study, we successfully produced FAST-PETase at a large scale using the silk gland expression system of Bombyx mori and integrated an optimized FAST-PETase gene into the B. mori genome using genetic engineering technology. The content of recombinant FAST-PETase reached 53.3 mg per gram of cocoon weight, and approximately 22 % of which can be extracted using mild extraction conditions. The analysis revealed that rFAST-PETase, when extracted from cocoon crude extracts, efficiently and completely hydrolyzes PET plastics into terephthalic acid (TPA) and ethylene glycol (EG). Notably, the extraction method did not affect the spinning properties of the silk. Furthermore, a unique N-glycosylation modification of rFAST-PETase in the silkworm system was identified, which led to a significant enhancement in its thermostability. In comparison with conventional hydrolysis strategies for PET plastics, the cost of the proposed method is reduced by a minimum of 72 %, and the TPA hydrolysis product with 99 % purity can be recycled through an acid precipitation method. These findings indicate that this genetically engineered silk material has potential for use in PET plastic waste recycling.