Discovery and characterization of outer membrane vesicles produced by the bee gut microbiota

Bacteria use diverse mechanisms to interact with each other and with eukaryotic hosts, thereby shaping microbiome composition and influencing host health. One of these mechanisms is the production of outer membrane vesicles (OMVs), nanoscale structures that bud off from bacterial cells into the extracellular space. OMVs can deliver bioactive cargoes, including enzymes, RNA and DNA, enabling functions such as cell-to-cell communication, nutrient acquisition and immunomodulation. However, the role of OMVs in beneficial host-associated microbiomes remains unclear. Here, we investigated OMV production in the gut bacteria of the western honeybee (Apis mellifera), which forms a highly conserved and stable microbial community. Using electron microscopy, fluorescence labelling and nanoparticle tracking analysis, we detected OMV production in every Gram-negative species of the bee gut microbiota that we investigated. Vesicles were observed in gut contents of wild and laboratory-inoculated bees, but absent in bees lacking a microbiota. OMVs contained nucleic acids, with more RNA than DNA. Bacterial strains varied in OMV properties, including abundance, size and zeta potential. These findings indicate that OMVs are likely significant mediators of interbacterial and host-microbe interactions in the bee gut.