Extracellular vesicles released by the human gut symbiont Bacteroides thetaiotaomicron in the mouse intestine are enriched in a selected range of proteins that influence host cell physiology and metabolism

It is becoming increasingly clear that bacterial extracellular vesicles (BEVs) produced by members of the intestinal microbiota can contribute to microbe-host cell interactions that impact on host health. A major unresolved question is the nature of the cargo packaged into these BEVs and how they can impact on host cell function. Here we have analysed the proteome of BEVs produced by the major human gut symbiont Bacteroides thetaiotaomicron in both in vitro cultures using defined and complex medias, and in vivo in fed or fasted animals to determine the impact of nutrient stress on the BEV proteome, and to identify proteins specifically enriched in BEVs produced in vivo. In contrast to BEVs produced in vitro where limiting nutrient provision resulted in an increase in a large fraction of proteins, the protein content of BEVs extracted from fasted versus fed mice was less affected with similar numbers of proteins showing increased and decreased abundance. We identified 102 proteins exclusively enriched in BEVs in vivo of which the majority (66/102) were enriched independently of their expression in the parent cells implicating the existence of an active mechanism to drive the selection of a group of proteins for their secretion into BEVs within the intestine. Amongst these abundantly expressed proteins in BEVs in vivo were a bile salt hydrolase and a dipeptidyl peptidase IV that were characterised further and shown to be active and able to degrade host-derived substrates with defined roles in metabolism. Collectively these findings provide additional evidence for the role of BEVs in microbiota-host interactions with their contents playing key roles in the maintenance of intestinal homeostasis, and host metabolism.