Proteomics Analysis Reveals Previously Uncharacterized Virulence Factors in Vibrio proteolyticus

Abstract

Members of the genus Vibrio include many pathogens of humans and marine animals that share genetic information via horizontal gene transfer. Hence, the Vibrio pan-genome carries the potential to establish new pathogenic strains by sharing virulence determinants, many of which have yet to be characterized. Here, we investigated the virulence properties of Vibrio proteolyticus, a Gram-negative marine bacterium previously identified as part of the Vibrio consortium isolated from diseased corals. We found that V. proteolyticus causes actin cytoskeleton rearrangements followed by cell lysis in HeLa cells in a contact-independent manner. In search of the responsible virulence factor involved, we determined the V. proteolyticus secretome. This proteomics approach revealed various putative virulence factors, including active type VI secretion systems and effectors with virulence toxin domains; however, these type VI secretion systems were not responsible for the observed cytotoxic effects. Further examination of the V. proteolyticus secretome led us to hypothesize and subsequently demonstrate that a secreted hemolysin, belonging to a previously uncharacterized clan of the leukocidin superfamily, was the toxin responsible for the V. proteolyticus-mediated cytotoxicity in both HeLa cells and macrophages. Clearly, there remains an armory of yet-to-be-discovered virulence factors in the Vibrio pan-genome that will undoubtedly provide a wealth of knowledge on how a pathogen can manipulate host cells.

Type VI secretion system MIX‐effectors carry both antibacterial and anti‐eukaryotic activities

“…To this end, we infected RAW 264.7 murine macrophages with Vpr . In agreement with our previous report , Vpr was cytotoxic to RAW 264.7 cells upon infection, and free nuclei from lysed cells were visible (Fig A). Remarkably, unmasking the VPRH‐mediated cytotoxicity by infecting macrophages with a Δ vprh mutant revealed dramatic morphological changes that were not detected upon infection of HeLa cells.…”

“…This cytotoxicity was mediated by a secreted pore‐forming hemolysin named VPRH . Strangely, however, unmasking this VPRH‐mediated cytotoxicity by infecting HeLa cells with a Δ vprh mutant did not reveal any observable actin cytoskeleton rearrangements . This result implied that the CNF1 MIX‐effector is either not a functional toxin or is not delivered into HeLa cells during infection.…”

“…We recently reported that Vpr induces cell death in human epithelial HeLa cells and in RAW 264.7 murine macrophages [35]. This cytotoxicity was mediated by a secreted pore-forming hemolysin named VPRH [35]. Strangely, however, unmasking this VPRHmediated cytotoxicity by infecting HeLa cells with a Dvprh mutant did not reveal any observable actin cytoskeleton rearrangements [35].…”

Transmission in the Origins of Bacterial Diversity, From Ecotypes to Phyla

“…That is, the familiar horizontal transfers of simple traits like antibiotic resistance and virulence, which plague public health (13,14), do not apply to phylum-defining qualities such as the Firmicutes' Gram-positive cell wall. The nontransferable nature of phylum-defining traits suggests that these are complex adaptations based on many genes and proteins (15,16).…”

Comparative pathogenicity of Vibrio spp., Photobacterium damselae ssp. damselae and five isolates of Aeromonas salmonicida ssp. achromogenes in juvenile Atlantic halibut (Hippoglossus hippoglossus)

“…The two Vibrio species that were tested in this study induced mortality rates of at least 45% and were originally isolated from dab ( Limanda limanda L.) and coal fish ( Pollachius virens (L.)). One of the Vibrios was identified as V. proteolyticus , a generalist pathogen that can infect a variety of marine animals (Ray et al., ). The other Vibrio isolate (MT1277) had a 62% match by Biolog as V. tubiashii which means that other Vibrio species may have been present as well.…”