Microbiota-host communications: Bacterial extracellular vesicles as a common language

Abstract

Both gram-negative and gram-positive bacteria release extracellular vesicles (EVs) that contain components from their mother cells. Bacterial EVs are similar in size to mammalian-derived EVs and are thought to mediate bacteria-host communications by transporting diverse bioactive molecules including proteins, nucleic acids, lipids, and metabolites. Bacterial EVs have been implicated in bacteria-bacteria and bacteria-host interactions, promoting health or causing various pathologies. Although the science of bacterial EVs is less developed than that of eukaryotic EVs, the number of studies on bacterial EVs is continuously increasing. This review highlights the current state of knowledge in the rapidly evolving field of bacterial EV science, focusing on their discovery, isolation, biogenesis, and more specifically on their role in microbiota-host communications. Knowledge of these mechanisms may be translated into new therapeutics and diagnostics based on bacterial EVs.

Fig 1. Bacterial EV biogenesis, composition, and functions.

(A) EVs derived from gram-negative bacteria can be released through the outer membrane (i) by decreased protein linkages between the outer membrane and peptidoglycan; (ii) by accumulation of unfolded proteins and/or fragments of peptidoglycan in the periplasmic space generating turgor pressure; and (iii) by explosive cell lysis. (B) EVs derived from gram-positive bacteria can be released through the cell wall (i) by turgor pressure caused by the accumulation of EVs; and (ii) by the action of cell wall–degrading enzymes. (C) Bacterial EV composition includes a double phospholipidic layer, proteins, glycoproteins, metabolites, and nucleic acids. Gram-negative EVs differentiate from gram-positive-derived EVs by the presence of LPS on their surface. (D) EV functions during the interactions between bacteria or host cells. EVs, extracellular vesicles; LPS, lipopolysaccharides.