Interaction of Bacteroides fragilis Toxin with Outer Membrane Vesicles Reveals New Mechanism of Its Secretion and Delivery

Abstract

The only recognized virulence factor of enterotoxigenic Bacteroides fragilis (ETBF) that accompanies bloodstream infections is the zinc-dependent non-lethal metalloprotease B. fragilis toxin (BFT). The isolated toxin stimulates intestinal secretion, resulting in epithelial damage and necrosis. Numerous publications have focused on the interrelation of BFT with intestinal inflammation and colorectal neoplasia, but nothing is known about the mechanism of its secretion and delivery to host cells. However, recent studies of gram-negative bacteria have shown that outer membrane vesicles (OMVs) could be an essential mechanism for the spread of a large number of virulence factors. Here, we show for the first time that BFT is not a freely secreted protease but is associated with OMVs. Our findings indicate that only outer surface-exposed BFT causes epithelial cell contact disruption. According to our in silico models confirmed by Trp quenching assay and NMR, BFT has special interactions with outer membrane components such as phospholipids and is secreted during vesicle formation. Moreover, the strong cooperation of BFT with polysaccharides is similar to the behavior of lectins. Understanding the molecular mechanisms of BFT secretion provides new perspectives for investigating intestinal inflammation pathogenesis and its prevention.

Dinoroseobacter shibae Outer Membrane Vesicles Are Enriched for the Chromosome Dimer Resolution Site dif

“…Serralysin-like proteins belong into the zinc-containing subfamily of extracellular metalloproteases and play fundamentally important roles in pathogenicity ( 67 ). The Bacteroides fragilis toxin (which is a zinc-dependent nonlethal metalloprotease) is delivered via OMVs to epithelial cells rather than being excreted directly into the extracellular medium ( 68 ). The vesicle lumen was enriched for two hemolysin-like calcium-binding proteins.…”

Staphylococcus aureusextracellular vesicles (EVs): surface-binding antagonists of biofilm formation

“…The production of EVs is widespread, with nearly all strains characterized thus far, including Gram-negative and Gram-positive, producing them. 24-26 The functions of EVs are as diverse as the hosts producing them, with them being used by different strains to transport proteins, including virulence factors, 27, 28 or DNA to other hosts. 29, 30 Recent studies have also found the production of EVs aid in the development of biofilms by some strains.…”

Bacterial outer membrane vesicles: New insights and applications

“…Outer membrane vesicles ($50-250 nm in diameter) are produced by both pathogenic and nonpathogenic bacteria and are involved in diverse functions such as mediating bacterial intercellular communication, promoting virulence, elimination of unwanted components and modulating host immune response (Bauman & Kuehn, 2009;Horstman & Kuehn, 2000;Ismail et al, 2003;Kulp & Kuehn, 2010;Mirlashari et al, 2001;Schwechheimer & Kuehn, 2015;Schwechheimer et al, 2013;Yaron et al, 2000). The diverse functions performed by OMVs are conferred by the different cargoes such as DNA (Deatherage et al, 2009;Renelli et al, 2004), RNA (Bernadac et al, 1998;Ghosal et al, 2015;Koeppen et al, 2016;Sjostrom et al, 2015), toxins (Bielaszewska et al, 2017;Horstman & Kuehn, 2000;Lindmark et al, 2009;Zakharzhevskaya et al, 2017) and many different proteins from the bacterial outer membrane (OM), periplasm and cytoplasm (Kaparakis-Liaskos & Ferrero, 2015) carried by OMVs. Important periplasmic components entrapped by OMVs include alkaline phosphatase, phospholipase C, proelastase, protease and peptidoglycan (PG) hydrolase (Li et al, 1998).…”