Bacterial membrane vesicles with multiple lipid bilayers: vesicles harboring organelle-like structures.

Bacteria produce outer membrane vesicles (OMVs), which are spherical nanoparticles that are mainly composed of lipopolysaccharides, phospholipids, and outer membrane proteins. OMVs play critical biological roles in stress responses, microbial communication, and bacteria-host interactions. Additionally, they hold great potential for biotechnological applications because of their versatile function in molecular transport while protecting the endogenous substances. While OMVs have been considered lipid monolamellar vesicles for several decades, recent studies have shown that membrane vesicles (MVs) with multiple lipid bilayers, including outer-inner membrane vesicles, multilamellar vesicles, and multivesicular vesicles, are also produced by Gram-negative bacteria. Some internal vesicles contain cytoplasmic components such as DNA and thus function as organelle-like structures within MVs. This review provides recent findings regarding the biogenesis and properties of MVs with complex structures.