Bacterial outer membrane vesicles and the host–pathogen interaction

Abstract

Extracellular secretion of products is the major mechanism by which Gram-negative pathogens communicate with and intoxicate host cells. Vesicles released from the envelope of growing bacteria serve as secretory vehicles for proteins and lipids of Gram-negative bacteria. Vesicle production occurs in infected tissues and is influenced by environmental factors. Vesicles play roles in establishing a colonization niche, carrying and transmitting virulence factors into host cells, and modulating host defense and response. Vesicle-mediated toxin delivery is a potent virulence mechanism exhibited by diverse Gram-negative pathogens. The biochemical and functional properties of pathogen-derived vesicles reveal their potential to critically impact disease.In nearly every case, virulence factors of Gram-negative pathogens are secreted products that enhance the survival of the bacteria and/or damage the host. Secretion of virulence factors by Gram-negative pathogens is complicated by the fact that the bacterial envelope consists of two lipid bilayers, the inner and outer membrane, and the periplasm in between. Gram-negative pathogens have developed many strategies, some specific to pathogens, to enable active virulence factors to gain access to the extracellular environment, typically the tissues or bloodstream of the host organism (Henderson et al. 2004). The Type II and Type V secretion systems are two-step processes in which proteins are transported first through the inner membrane (IM) and then through the outer membrane (OM). For secretion via the Type I, Type III, and Type IV secretion systems, the material is transferred directly into the extracellular milieu or into another cell. The Type III system is specific for the transport of factors by pathogenic bacteria. All of these secretion systems secrete individual proteins or small complexes. This review examines secretion via OM vesicles, a distinct "Type VI" mechanism that enables bacteria to secrete a large, complex group of proteins and lipids into the extracellular milieu.Both pathogenic and nonpathogenic species of Gram- Vesicles are a means by which bacteria interact with prokaryotic and eukaryotic cells in their environment. Some of the best-characterized vesicles are those produced by pathogens. Biochemical analysis and functional characterization of pathogen-derived outer membrane vesicles demonstrate that this secretory pathway has been usurped by pathogens for the transport of active virulence factors to host cells (Table 1). Naturally produced OM vesicles from pathogenic bacteria contain adhesins, toxins, and immunomodulatory compounds, and they directly mediate bacterial binding and invasion, cause cytotoxicity, and modulate the host immune response. By participating in such diverse aspects of the host-pathogen interaction, OM vesicles are potent bacterial virulence factors. Formation of bacterial OM vesiclesNaturally produced bacterial vesicles are discrete, closed OM blebs produced by growing cells, not products of cell lysis or cell death (Mug-Opstelte...

Origin of life: LUCA and extracellular membrane vesicles (EMVs)

“…For many decades the formation of EMVs in prokaryotes was solely focused on bacteria (Kuehn & Kesty 2005;Ellis & Kuehn 2010;Kulp & Kuehn 2010). In bacteria with double membranes (referred to as diderm bacteria) they are generally derived from the outer membrane (OM) which is distinct from the cytoplasmic membrane, and are referred to as OMVs (Kulp & Kuehn 2010).…”

“…OMVs are potent virulence factors of pathogenic diderm bacteria. These vesicles contain toxins, DNA, immunomodulatory compounds, communication factors and adhesins, and have been associated with cytotoxicity, bacterial attachment, intercellular DNA transfer and invasion (Dorward et al 1989;Kuehn & Kesty 2005;Ellis & Kuehn 2010;Maldonado et al 2011;Brown et al 2014). Increased vesiculation has been linked to bacterial stress and may play a role in carrying away toxic compounds, phages or unfolded proteins after exposure to stressful conditions (McBroom & Kuehn 2007;Macdonald & Kuehn 2013).…”

Pseudomonas Quinolone Signal Affects Membrane Vesicle Production in not only Gram-Negative but also Gram-Positive Bacteria

“…coli naturally produces MVs under laboratory conditions and has been used as a model Gram-negative bacterium in studies of MVs (18,19). We investigated whether PQS induces MV production in E. coli K12.…”

“…These bilayered spheres contain phospholipids, lipopolysaccharide (LPS), DNA and several hydrolytic enzymes. Since MVs contain multiple virulence factors and deliver them to the host, they have been studied well in many Gram-negative pathogens (18). P. aeruginosa MVs also have a role as carriers of PQS and several AHQs (24,27).…”

“…Many Gram-negative bacteria release membrane vesicles (MVs) in the external milleu (18,19,25). These bilayered spheres contain phospholipids, lipopolysaccharide (LPS), DNA and several hydrolytic enzymes.…”