Updated project metadata. Secreted particles, including membrane vesicles, have increasingly been recognized as important for bacterial community functions and host-interaction processes, but their specific compositions and functional roles are debated. In this study, we have characterized the secreted particles of Apilactobacillus kunkeei, a defensive symbiont of honeybees. We cultivated A. kunkeei strains A1401 and A0901 and separated the secreted protein particles from the extracellular membrane vesicles using density gradient ultracentrifugation. A proteomics analyses identified more than 500 proteins in each strain, of which 27 to 45 proteins were relatively more abundant in the cell-free supernatant, including glycoside hydrolases and peptidases. The extracellular transcriptome associated with the membrane vesicles contained a relatively higher fraction of mRNAs derived from highly transcribed operons such as those for ribosomal proteins and ATP synthase subunits, whereas highly expressed tRNAs were relatively more abundant in the cellular fraction. Based on these results, we propose that mRNAs for highly expressed proteins are overproduced and that superfluous mRNAs are fragmented, packaged into membrane vesicles and secreted. The results have implications for the utilization of membrane vesicles in A. kunkeei as a delivery tool for small RNA molecules, while also providing more general insights into the role of membrane vesicles in bacteria.