Special delivery - extracellular vesicles released by commensal gut bacteria deliver bioactive protein to distal organs

<b>Aim:</b> This study aims to investigate how the gut microbiota communicates with the host via bacterial extracellular vesicles (BEVs), given that direct contact between microbes and the healthy intestinal epithelium is prevented by a sterile mucin gel layer. Understanding these indirect interactions is critical because the specific pathways and mediators of microbiota-host interactions are incompletely understood. Tracking BEVs <i>in vivo</i> however is particularly challenging due to their nanoscale size and complex molecular composition. <b>Methods:</b> To address these challenges, we developed a highly sensitive Nanoluciferase (NanoLuc) system for luminescence-based detection of BEVs produced by the model human commensal bacterium <i>Bacteroides thetaiotaomicron</i>. This approach was evaluated in germ-free and specific-pathogen-free mice, with comparisons between administration routes demonstrating the advantages of this system for <i>in vivo</i> BEV labelling over conventional lipophilic dyes. <b>Results:</b> We report, for the first time, that BEVs endogenously produced in the gastrointestinal tract (GIT) of mice can deliver bioactive NanoLuc protein to multiple organ tissues, including the central nervous system. Our findings establish that naturally occurring BEVs in the GIT are capable of traversing multiple host barriers, including the intestinal epithelium, vascular endothelium, and the blood-brain-barrier, to access tissues such as the brain and eyes. <b>Conclusion:</b> These findings advance our understanding of BEV-mediated microbe-host interactions and demonstrate the potential of BEVs as vehicles for long-distance delivery of bioactive therapeutics.