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

Abstract

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.

Genetically modifying the protein matrix of macroscopic living materials to control their structure and rheological properties

“…First, the longer ELPs could act as more flexible linkers, decreasing the nucleation of individual fibers and thus decreasing their width. A similar phenomenon was observed with silk fibers that nucleated on the surface of B. subtilis : silk peptides with less flexible linkers increased nucleation leading to thicker fibers 33 . An alternative explanation is that the decreasing fiber thickness arises from increasing hydrophobicity of the longer ELPs.…”