Bacterial outer membrane vesicles

Bacteria communicate among themselves and with other living forms in their environment via nano-scale membrane vesicles in their bacterial outer membranes. These vesicles are involved in trafficking bacterial cell signaling biochemicals, which may include DNA, RNA, proteins, endotoxins and allied virulence molecules. This communication happens in microbial cultures to oceans, inside animal/plant hosts and wherever bacteria may thrive. Gram negative microorganisms deploy their periplasm to secrete bacterial outer membrane vesicles (OMVs) for trafficking bacterial biochemicals to target cells in their environment (Fig. 1); OMVs also carry endotoxic lipopolysaccharide initiating disease process in their host. This mechanism imparts a variety of benefits like, long-distance delivery of bacterial secretory cargo with minimized hydrolytic degradation and extra-cellular dilution, also supplemented with other supportive molecules (e.g., virulence factors) to accomplish a specific job and yet, keeping a safe-distance from the defense arsenal of the targeted cells. Biochemical signals trafficked by OMVs may vary largely during 'war and peace' situations. In 'complacent' bacterial colonies, OMVs may be used to carry DNA to 'related' microbes for genetic transformations, and also translocate cell signaling molecules for quorum sensing and biofilm formation. During 'challenge' from other cell types around, OMVs may be preferred to carry degradation and subversion enzymes. Likewise, OMVs may contain more of invasion proteins at the host-pathogen interface (Fig. 1). It is expected, that environmental factors around the secretory microbes are responsible for inducing these bacteria to synthesize and secrete specifically-enriched OMVs, physiologically suiting the immediate task. Thus, bacterial OMVs, being strong immunomodulators, can be manipulated for their immunogenic contents and utilized as potent pathogen-free vaccines for immunizing humans and animals against threatening infections.

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