Release of the type I secreted α‐haemolysin via outer membrane vesicles from Escherichia coli

Abstract

SummaryThe α α α α -haemolysin is an important virulence factor commonly expressed by extraintestinal pathogenic Escherichia coli . The secretion of the α α α α -haemolysin is mediated by the type I secretion system and the toxin reaches the extracellular space without the formation of periplasmic intermediates presumably in a soluble form. Surprisingly, we found that a fraction of this type I secreted protein is located within outer membrane vesicles (OMVs) that are released by the bacteria. The α α α α -haemolysin appeared very tightly associated with the OMVs as judged by dissociation assays and proteinase susceptibility tests. The α α α α -haemolysin in OMVs was cytotoxically active and caused lysis of red blood cells. The OMVs containing the α α α α -haemolysin were distinct from the OMVs not containing α α α α -haemolysin, showing a lower density. Furthermore, they differed in protein composition and one component of the type I secretion system, the TolC protein, was found in the lower density vesicles. Studies of natural isolates of E. coli demonstrated that the localization of α α α α -haemolysin in OMVs is a common feature among haemolytic strains. We propose an alternative pathway for the transport of the type I secreted α α α α -haemolysin from the bacteria to the host cells during bacterial infections.

TdeA, a TolC-like protein required for toxin and drug export in Aggregatibacter (Actinobacillus) actinomycetemcomitans

“…Because RTX toxins are transported through the bacterial cell envelope without a periplasmic intermediate (Gray et al, 1986;Koronakis et al, 2004), LtxA would have to be exported through TdeA before localizing to the outer membrane or within vesicles. Observations about LtxA localization fit the model proposed by Balsalobre et al (Balsalobre et al, 2006), who recently reported that E. coli α -hemolysin localization to outer membranederived vesicles occurs upon assembly of the complete type I secretion machinery.…”

Proteomic analysis of secreted membrane vesicles of archaeal Sulfolobus species reveals the presence of endosome sorting complex components

“…In gram-negative bacteria, several functions have been attributed to the release of outer membrane vesicles such as DNA and protein secretion, cell to cell communication and a stress response to cell envelope damage. For example, the a-hemolysin toxin of Escherichia coli is released in association with outer membrane vesicles (Balsalobre et al 2006), while denatured proteins at the cell envelope are expelled from the cell via outer membrane vesicles (McBroom and Kuehn 2007). Outer membrane vesicles produced by Pseudomonas aeruginosa are equipped with antimicrobial activity and have been implicated in quorum sensing allowing individual cells to act as a group (Mashburn and Whiteley 2005).…”

Aggregatibacter actinomycetemcomitans Outer Membrane Vesicles Are Internalized in Human Host Cells and Trigger NOD1- and NOD2-Dependent NF-κB Activation

“…Via MVs, bacteria can expose host cells to relatively high concentrations of toxins and additional virulence factors without the requirement of a close contact between the bacterial and target mammalian cells (2)(3)(4)(5)(6)(7)(8)(9). MVs have also several defensive functions, including a role in antimicrobial peptide resistance (6,10).…”