Types and origins of bacterial membrane vesicles

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Abstract

Most bacteria release membrane vesicles (MVs) that contain specific cargo molecules and have diverse functions, including the transport of virulence factors, DNA transfer, interception of bacteriophages, antibiotics and eukaryotic host defence factors, cell detoxification and bacterial communication. MVs not only are abundant in nature but also show great promise for applications in biomedicine and nanotechnology. MVs were first discovered to originate from controlled blebbing of the outer membrane of Gram-negative bacteria and are therefore often called outer-membrane vesicles (OMVs). However, recent work has shown that Gram-positive bacteria can produce MVs, that different types of MVs besides OMVs exist and that, in addition to membrane blebbing, MVs can also be formed by endolysin-triggered cell lysis. In this Review, we provide an overview of the structures and compositions of the various vesicle types and discuss novel formation routes, which may lead to distinct vesicle types that serve particular functions.

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Explosive cell lysis as a mechanism for the biogenesis of bacterial membrane vesicles and biofilms

Lynne Turnbull, Masanori Toyofuku, Amelia L. Hynen … (2016)

Many bacteria produce extracellular and surface-associated components such as membrane vesicles (MVs), extracellular DNA and moonlighting cytosolic proteins for which the biogenesis and export pathways are not fully understood. Here we show that the explosive cell lysis of a sub-population of cells accounts for the liberation of cytosolic content in Pseudomonas aeruginosa biofilms. Super-resolution microscopy reveals that explosive cell lysis also produces shattered membrane fragments that rapidly form MVs. A prophage endolysin encoded within the R- and F-pyocin gene cluster is essential for explosive cell lysis. Endolysin-deficient mutants are defective in MV production and biofilm development, consistent with a crucial role in the biogenesis of MVs and liberation of extracellular DNA and other biofilm matrix components. Our findings reveal that explosive cell lysis, mediated through the activity of a cryptic prophage endolysin, acts as a mechanism for the production of bacterial MVs.

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The role of extracellular DNA in the establishment, maintenance and perpetuation of bacterial biofilms.

Mira Okshevsky, Charles Meyer (2013)

Abstract The significance of extracellular DNA (eDNA) in biofilms was overlooked until researchers added DNAse to a Pseudomonas aeruginosa biofilm and watched the biofilm disappear. Now, a decade later, the widespread importance of eDNA in biofilm formation is undisputed, but detailed knowledge about how it promotes biofilm formation and conveys antimicrobial resistance is only just starting to emerge. In this review, we discuss how eDNA is produced, how it aids bacterial adhesion, secures the structural stability of biofilms and contributes to antimicrobial resistance. The appearance of eDNA in biofilms is no accident: It is produced by active secretion or controlled cell lysis - sometimes linked to competence development. eDNA adsorbs to and extends from the cell surface, promoting adhesion to abiotic surfaces through acid-base interactions. In the biofilm, is it less clear how eDNA interacts with cells and matrix components. A few eDNA-binding biomolecules have been identified, revealing new concepts in biofilm formation. Being anionic, eDNA chelates cations and restricts diffusion of cationic antimicrobials. Furthermore, chelation of Mg(2+) triggers a genetic response that further increases resistance. The multifaceted role of eDNA makes it an attractive target to sensitize biofilms to conventional antimicrobial treatment or development of new strategies to combat biofilms.

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Virulence factors are released from Pseudomonas aeruginosa in association with membrane vesicles during normal growth and exposure to gentamicin: a novel mechanism of enzyme secretion.

J Kadurugamuwa, T. J. Beveridge (1995)

Pseudomonas aeruginosa blebs-off membrane vesicles (MVs) into culture medium during normal growth. Release of these vesicles increased approximately threefold after exposure of the organism to four times the MIC of gentamicin. Natural and gentamicin-induced membrane vesicles (n-MVs and g-MVs and g-MVs, respectively) were isolated by filtration and differential centrifugation, and several of their biological activities were characterized. Electron microscopy of both n-MVs and g-MVs revealed that they were spherical bilayer MVs with a diameter of 50 to 150 nm. Immunoelectron microscopy and Western blot (immunoblot) analysis of the vesicles demonstrated the presence of B-band lipopolysaccharide (LPS), with a slightly higher proportion of B-band LPS in g-MVs than in n-MVs. A-band LPS was occasionally detected in g-MVs but not in n-MVs. In addition to LPS, several enzymes, such as phospholipase C, protease, hemolysin, and alkaline phosphatase, which are known to contribute to the pathogenicity of Pseudomonas infections were found to be present in both vesicle types. Both types of vesicles contained DNA, with a significantly higher content in g-MVs. These vesicles could thus play an important role in genetic transformation and disease by serving as a transport vehicle for DNA and virulence factors and are presumably involved in septic shock.