Secretion-Catalyzed Assembly of Protein Biomaterials on a Bacterial Membrane Surface

Protein-based biomaterials have played a key role in tissue engineering, and additional exciting applications as self-healing materials and sustainable polymers are emerging. Over the past few decades, recombinant expression and production of various fibrous proteins from microbes have been demonstrated; however, the resulting proteins typically must then be purified and processed by humans to form usable fibers and materials. Here, we show that the Gram-positive bacterium Bacillus subtilis can be programmed to secrete silk through its translocon via an orthogonal signal peptide/peptidase pair. Surprisingly, we discover that this translocation mechanism drives the silk proteins to assemble into fibers spontaneously on the cell surface, in a process we call secretion-catalyzed assembly (SCA). Secreted silk fibers form self-healing hydrogels with minimal processing. Alternatively, the fibers retained on the membrane provide a facile route to create engineered living materials from Bacillus cells. This work provides a blueprint to achieve autonomous assembly of protein biomaterials in useful morphologies directly from microbial factories.

Automated summary

Protein-based biomaterials have important roles in tissue engineering and have potential applications as self-healing materials and sustainable polymers. Researchers have discovered that the bacterium Bacillus subtilis can be genetically engineered to secrete silk proteins, which spontaneously assemble into fibers on the cell surface in a process known as secretion-catalyzed assembly (SCA). These secreted silk fibers can form self-healing hydrogels without additional processing, and the fibers retained on the bacterial membrane can be used to create engineered living materials. This study provides a blueprint for the autonomous assembly of protein biomaterials directly from microbial factories.