PEARL: Protein Eluting Alginate with Recombinant Lactobacilli

Engineered living materials (ELMs) made of bacteria in hydrogels have shown considerable promise for therapeutic applications since they offer the possibility to achieve controlled and prolonged release of complex biopharmaceuticals at low costs and with reduced wastage. While most therapeutic ELMs use E. coli as the living component due to its large genetic toolbox, most live biotherapeutic bacteria in clinical trials are lactic acid bacteria due to the native health benefits they offer. Among these, lactobacilli are the largest family of probiotic bacteria that are being investigated for their therapeutic potential in almost all sites of the body that host a microbiome. A major factor limiting the use of lactobacilli in ELMs is their limited genetic toolbox. In this study, we build upon our recent work to expand the genetic programmability of a probiotic lactobacillus strain (Lactiplantibacillus plantarum WCFS1) for protein secretion and integrate it into a simple, cost-effective, and biocompatible alginate bead encapsulation format to develop an ELM. We demonstrate the controlled release of a recombinant protein for up to 14 days from this ELM, thereby terming it PEARL - Protein Eluting Alginate with Recombinant Lactobacilli. Notably, encapsulation of the lactobacilli offered multiple benefits such as preventing bacterial outgrowth, stabilizing protein release profiles over time, and preventing potential cytotoxicity caused by bacterial metabolites. These findings demonstrate the mutual benefits of combining recombinant lactobacilli with alginate for the controlled release of proteins for biomedical applications.