Sodium Taurocholate Stimulates Campylobacter jejuni Outer Membrane Vesicle Production via Down-Regulation of the Maintenance of Lipid Asymmetry Pathway

Abstract

Campylobacter jejuni outer membrane vesicles (OMVs) contain numerous virulence-associated proteins including the cytolethal distending toxin and three serine proteases. As C. jejuni lacks the classical virulence-associated secretion systems of other enteric pathogens that deliver effectors directly into target cells, OMVs may have a particularly important role in virulence. C. jejuni OMV production is stimulated by the presence of physiological concentrations of the bile salt sodium taurocholate (ST) through an unknown mechanism. The maintenance of lipid asymmetry (MLA) pathway has been implicated in a novel mechanism for OMV biogenesis, open to regulation by host signals. In this study we investigated the role of the MLA pathway in C. jejuni OMV biogenesis with ST as a potential regulator. OMV production was quantified by analyzing protein and lipid concentrations of OMV preparations and OMV particle counts produced by nanoparticle tracking analysis. Mutation of mlaA which encodes the outer membrane component of the MLA pathway significantly increased OMV production compared to the wild-type strain. Detergent sensitivity and membrane permeability assays confirmed the increased OMV production was not due to changes in membrane stability. The presence of 0.2% (w/v) ST increased wild-type OMV production and reduced OMV size, but did not further stimulate mlaA mutant OMV production or significantly alter mlaA mutant OMV size. qRT-PCR analysis demonstrated that the presence of ST decreased expression of both mlaA and mlaC in C. jejuni wild-type strains 11168 and 488. Collectively the data in this study suggests C. jejuni can regulate OMV production in response to host gut signals through changes in expression of the MLA pathway. As the gut bile composition is dependent on both diet and the microbiota, this study highlights the potential importance of diet and lifestyle factors on the varying disease presentations associated with gut pathogen infection.

Membrane Vesicle Production as a Bacterial Defense Against Stress

“…Most studies to date on membrane vesiculation have focused on Gram-negative bacteria (and hence, OMVs). However, recently there has been increasing interest in the regulatory role of the inner membrane ( Davies et al, 2019 ; Takaki et al, 2020 ). The role of inner membrane in outer membrane vesiculation could be considered via various aspects, including (I) Inner membrane regulates and keeps the cross-talk between the components of the bacterial envelope, e.g., outer membrane-peptidoglycan-inner membrane, (II) Inner membrane regulates the stress response-pathway, (III) Inner membrane contains maintenance elements for outer membrane asymmetry (IV) Inner membrane can convey the turgor pressure of misfolded proteins and SOS response-pathway to periplasm and outer membrane.…”

“…(III) Inner membrane and envelope asymmetry. The inner membrane is a key element in the maintenance of the membrane lipid asymmetry (MLA) pathway regulating membrane vesiculation ( Davies et al, 2019 ). In the asymmetric outer membrane, the outer leaflet harbors lipopolysaccharides whereas the inner leaflet is mostly composed of phospholipids.…”

“…The presence of nutrient-absorbing molecules on the surface of OMVs induced by starvation enhances the dispersal of these molecules in the environment. Upon nutrient deficiency, the cell downregulates components of the MLA system ( Manning and Kuehn, 2011 ; Zingl et al, 2020 ), resulting in the release of membrane vesicles with nutrient-absorbing molecules such as iron chelators on their surface ( Roier et al, 2016 ; Davies et al, 2019 ).…”

Biofilm formation and extracellular microvesicles—The way of foodborne pathogens toward resistance

“…After treatment with this bile salt, C. jejuni outer MV production increased, with increased MVs-associated proteolytic activity as a consequence. Recently, Davies et al [186] also showed that the production of MVs by C. jejuni is stimulated after addition of physiological concentrations of sodium taurocholate. In the host organism, bile salts are according to Stieger [187]: "A major constituent of bile and are secreted by hepatocytes into bile and delivered into the small intestine, where they assist in fat digestion."…”

Microbe Profile: Campylobacter jejuni – survival instincts

“…C. jejuni is able to modify the CCV to meet its metabolic needs and also interfere with the canonical endocytic pathway, preventing C. jejuni killing within lysosomes [6]. Outer membrane vehicles have also been explored which can act as cargo delivery vehicles, possibly containing and delivering virulence-related proteins [7].…”