A Universal Strategy to Promote Secretion of G+/G- Bacterial Extracellular Vesicles and Its Application in Host Innate Immune Responses.

Both Gram-positive and Gram-negative bacteria release nanosized extracellular vesicles called membrane vesicles (MVs, 20-400 nm), which have great potential in various biomedical applications due to their abilities to deliver effector molecules and induce therapeutic responses. To fully utilize bacterial MVs for therapeutic purposes, regulated and enhanced production of MVs would be highly advantageous. In this study, we developed a universal method to enhance MV yields in both G+/G- bacteria through an autonomous controlled peptidoglycan hydrolase (PGase) expression system. A significant increase (9.37-fold) of MV concentration was observed in engineered E. coli Nissle 1917 compared to the wild-type. With the help of this autonomous system, for the first time we experimentally confirmed horizontal gene transfer and nutrient acquisition in a cocultured bacterial consortium. Furthermore, the engineered probiotic E. coli strains with high yield of MVs showed higher activation of the innate immune responses in human embryonic kidney 293T (HEK293T) and human colorectal carcinoma cells (HCT116), thereby demonstrating the great potential of engineering probiotics in immunology and further living therapeutics in humans.