Biological characterization of a new type III secretion system effector from a clinical isolate of Aeromonas hydrophila—Part II

Sierra, Johanna C.; Suárez, Giovanni; Sha, Jian; Foltz, Sheri M.; Popov, Vsevolod L.; Galindo, Cristi L.; Garner, Harold R.; Chopra, Ashok K.

doi:10.1016/j.micpath.2007.05.003

Cited by 40 publications

(76 citation statements)

References 42 publications

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“…A novel type 3 secretion system (T3SS) effector has been identified, AexU, which disrupts host macrophages and promotes their apoptosis by ADP-ribosyltranserfase as well as GTPaseactivating protein activity (Sierra et al, 2007;Sierra et al, 2010). Whereas the T3SS serves as an injectisome that translocates bacterial toxins directly into the host cell cytoplasm, A. hydrophila's second major weapon serves as both an injectisome, like the T3SS, as well as a secretion apparatus that allows some microbial toxins to be secreted extracellularly, promoting bacterial dissemination.…”

Section: Introductionmentioning

confidence: 99%

Evaluation of the roles played by Hcp and VgrG type 6 secretion system effectors in Aeromonas hydrophila SSU pathogenesis

et al. 2013

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Aeromonas hydrophila, a Gram-negative bacterium, is an emerging human pathogen equipped with both a type 3 and a type 6 secretion system (T6SS). In this study, we evaluated the roles played by paralogous T6SS effector proteins, hemolysin co-regulated proteins (Hcp-1 and -2) and valine glycine repeat G (VgrG-1, -2 and -3) protein family members in A. hydrophila SSU pathogenesis by generating various combinations of deletion mutants of the their genes. In addition to their predicted roles as structural components and effector proteins of the T6SS, our data clearly demonstrated that paralogues of Hcp and VgrG also influenced bacterial motility, protease production and biofilm formation. Surprisingly, there was limited to no observed functional redundancy among and/or between the aforementioned T6SS effector paralogues in multiple assays. Our data indicated that Hcp and VgrG paralogues located within the T6SS cluster were more involved in forming T6SS structures, while the primary roles of Hcp-1 and VgrG-1, located outside of the T6SS cluster, were as T6SS effectors. In terms of influence on bacterial physiology, Hcp-1, but not Hcp-2, influenced bacterial motility and protease production, and in its absence, increases in both of the aforementioned activities were observed. Likewise, VgrG-1 played a major role in regulating bacterial protease production, while VgrG-2 and VgrG-3 were critical in regulating bacterial motility and biofilm formation. In an intraperitoneal murine model of infection, all Hcp and VgrG paralogues were required for optimal bacterial virulence and dissemination to mouse peripheral organs. Importantly, the observed phenotypic alterations of the T6SS mutants could be fully complemented. Taking these results together, we have further established the roles played by the two known T6SS effectors of A. hydrophila by defining their contributions to T6SS function and virulence in both in vitro and in vivo models of infection.

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Section: Introductionmentioning

confidence: 99%

Evaluation of the roles played by Hcp and VgrG type 6 secretion system effectors in Aeromonas hydrophila SSU pathogenesis

et al. 2013

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“…This effector induced a rounded phenotype when its corresponding gene was expressed in HeLa Tet-Off cells (43). In addition, the results of our previous study indicated that the production and translocation of AexU was not altered when the vasH gene was deleted from the parental A. hydrophila strain; however, this vasH mutant showed delayed cytotoxicity in HeLa cells, as well as in RAW 264.7 murine macrophages (44).…”

Section: Discussionmentioning

confidence: 94%

“…We evaluated the extent of apoptosis of HeLa Tet-Off cells expressing different vgrG1 fragments by detection of cytoplasmic nucleosomes and measurement of caspase 3 and 9 activation, as we previously described (43).…”

Section: Methodsmentioning

confidence: 99%

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A Type VI Secretion System Effector Protein, VgrG1, from Aeromonas hydrophila That Induces Host Cell Toxicity by ADP Ribosylation of Actin

et al. 2010

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We recently delineated the importance of a type VI secretion system (T6SS) gene cluster in the virulence of diarrheal isolate SSU of Aeromonas hydrophila and showed that VasH, a 54 activator and T6SS component, was involved in the production of its associated effectors, e.g., hemolysin-coregulated protein. To identify additional T6SS effectors and/or secreted proteins, we subjected culture supernatants from deletion mutants of A. hydrophila, namely, a ⌬act mutant (a T2SS-associated cytotoxic enterotoxin-encoding gene) and a ⌬act ⌬vasH mutant, to 2-dimensional gel electrophoresis and mass spectrometric analysis. Based on these approaches, we identified a member of the VgrG protein family, VgrG1, that contained a vegetative insecticidal protein (VIP-2) domain at its carboxyl-terminal end. Consequently, the vgrG1 gene was cloned in pBI-EGFP and pET-30a vectors to be expressed in HeLa Tet-Off cells and Escherichia coli, respectively. We assessed the ADP-ribosyltransferase (ADPRT) activity of various domains of purified recombinant VgrG1 (rVgrG1) and provided evidence that only the full-length VgrG1, as well as its carboxyl-terminal domain encoding the VIP-2 domain, showed ADPRT activity. Importantly, bacterium-host cell interaction was needed for the T6SS to induce cytotoxicity in eukaryotic cells, and we demonstrated translocation of VgrG1. Furthermore, our data indicated that expression of the genes encoding the full-length VgrG1 and its carboxyl-terminal domain in HeLa Tet-Off cells disrupted the actin cytoskeleton, which was followed by a decrease in cell viability and an increase in apoptosis. Taken together, these findings demonstrated for the first time that VgrG1 of A. hydrophila possessed actin ADPRT activity associated with its VIP-2 domain and that this domain alone was able to induce a rounded phenotype in HeLa Tet-Off cells, followed by apoptosis mediated by caspase 9 activation.

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“…For example, a functional T3SS and 2 T3SS effectors have been identified in aeromonads and have been found to cause host cell death. 23,24 Likewise, the T6SS effector hemolysin co-regulated protein reduces A. hydrophila uptake by macrophages and interferes with macrophage activation and maturation by inhibiting proinflammatory cytokines and inducing immunosuppressive cytokines. 25 An outer membrane endopeptidase of A. hydrophila activates big endothelin-3 and is required to induce pathognomonic skin ulcers.…”

Section: Discussionmentioning

confidence: 99%

Contribution of nuclease to the pathogenesis of Aeromonas hydrophila

Qin

et al. 2015

Virulence

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These authors contributed equally to this work. Keywords: Aeromonas hydrophila, nuclease, pathogenesisAeromonas hydrophila is a gram-negative bacterium that is widely distributed in aquatic environments and can cause septicemia in both fish and humans. However, the underlying mechanisms leading to severe infection are not well understood. In this study, an A. hydrophila nuclease (ahn) deletion mutant was constructed to investigate its contribution to pathogenesis. This mutant did not differ from the wild-type strain in terms of its growth or hemolytic phenotype. However, the ahn-deficient mutant was more susceptible to being killed by fish macrophages and mouse blood in vitro. Furthermore, evidence obtained using both fish and murine infection models strongly indicated that the inactivation of Ahn impaired the ability of A. hydrophila to evade innate immune clearance in vivo. More importantly, the virulence of the mutant was attenuated in both fish and mice, with reductions in dissemination capacities and mortality rates. These findings implicate Ahn in A. hydrophila virulence, with important functions in evading innate immune defenses.

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Biological characterization of a new type III secretion system effector from a clinical isolate of Aeromonas hydrophila—Part II

Cited by 40 publications

References 42 publications

Evaluation of the roles played by Hcp and VgrG type 6 secretion system effectors in Aeromonas hydrophila SSU pathogenesis

Evaluation of the roles played by Hcp and VgrG type 6 secretion system effectors in Aeromonas hydrophila SSU pathogenesis

A Type VI Secretion System Effector Protein, VgrG1, from Aeromonas hydrophila That Induces Host Cell Toxicity by ADP Ribosylation of Actin

Contribution of nuclease to the pathogenesis of Aeromonas hydrophila

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