Biodegradation of β-Sheet Crystal-Rich Silk Fibroin Bioplastic Promoted by Functionally Active Soil Microbiome

Bioplastics have been developed as alternatives to petrochemical plastics. The microbial biodegradation process is driven by enzymes involved in microbial metabolism. Amorphous structures that enhance enzyme affinity and biodegradation rates often compromise mechanical and thermal properties. In contrast, although crystal domain-rich bioplastics may exhibit excellent physical characteristics, they typically suffer from insufficient biodegradability. In this study, we explored the balance between crystallinity, enzymatic stability, and biodegradability. Our model Bioplastic is a silk fibroin Bioplastic that demonstrates a high β-sheet crystal content and enzyme-resistance, which contrasts with the properties of conventional silk fibroin materials. When buried in microbially activated compost soil, this Bioplastic achieves a notable composting rate of 72.1% over 8 weeks. Soil microbiome analysis revealed that compost maturation increases species diversity within microbial communities, enriching silk-degrading enzymes that accelerate biodegradation. This finding was further validated in biodegradation tests using commercial nursery soils containing plant materials. Taken together, soil microbiome activity emerges as one of the principal factors in eliciting the biodegradability of crystal-rich, enzyme-resistant bioplastics. Our work will contribute to developing future bioplastics that combine superior physical properties and high biodegradability.