scholarly journals OpiA, a Type Six Secretion System Substrate, Localizes to the Cell Pole and Plays a Role in Bacterial Growth and Viability in Francisella tularensis LVS

2020 ◽  
Vol 202 (14) ◽  
Author(s):  
Stuart Cantlay ◽  
Kristen Haggerty ◽  
Joseph Horzempa
Keyword(s):  
Cell Size ◽  
Francisella Tularensis ◽  
Secretion System ◽  
Live Vaccine ◽  
Intracellular Pathogen ◽  
Content Type ◽  
Erythrocyte Invasion ◽  
Host Pathogen

ABSTRACT Francisella tularensis is an intracellular pathogen and the causative agent of tularemia. The F. tularensis type six secretion system (T6SS) is required for a number of host-pathogen interactions, including phagolysosomal escape and invasion of erythrocytes. One known effector of the T6SS, OpiA, has recently been shown to be a phosphatidylinositol-3 kinase. To investigate the role of OpiA in erythrocyte invasion, we constructed an opiA-null mutant in the live vaccine strain, F. tularensis LVS. OpiA was not required for erythrocyte invasion; however, deletion of opiA affected growth of F. tularensis LVS in broth cultures in a medium-dependent manner. We also found that opiA influenced cell size, gentamicin sensitivity, bacterial viability, and the lipid content of F. tularensis. A fluorescently tagged OpiA (OpiA–emerald-green fluorescent protein [EmGFP]) accumulated at the cell poles of F. tularensis, which is consistent with the location of the T6SS. However, OpiA-EmGFP also exhibited a highly dynamic localization, and this fusion protein was detected in erythrocytes and THP-1 cells in vitro, further supporting that OpiA is secreted. Similar to previous reports with F. novicida, our data demonstrated that opiA had a minimal effect on intracellular replication of F. tularensis in host immune cells in vitro. However, THP-1 cells infected with the opiA mutant produced modestly (but significantly) higher levels of the proinflammatory cytokine tumor necrosis factor alpha compared to these host cells infected with wild-type bacteria. We conclude that, in addition to its role in host-pathogen interactions, our results reveal that the function of opiA is central to the biology of F. tularensis bacteria. IMPORTANCE F. tularensis is a pathogenic intracellular pathogen that is of importance for public health and strategic defense. This study characterizes the opiA gene of F. tularensis LVS, an attenuated strain that has been used as a live vaccine but that also shares significant genetic similarity to related Francisella strains that cause human disease. The data presented here provide the first evidence of a T6SS effector protein that affects the physiology of F. tularensis, namely, the growth, cell size, viability, and aminoglycoside resistance of F. tularensis LVS. This study also adds insight into our understanding of OpiA as a determinant of virulence. Finally, the fluorescence fusion constructs presented here will be useful tools for dissecting the role of OpiA in infection.

scholarly journals Regulation by ToxR-Like Proteins Converges onvttRBExpression To Control Type 3 Secretion System-Dependent Caco2-BBE Cytotoxicity in Vibrio cholerae

2016 ◽  
Vol 198 (11) ◽  
pp. 1675-1682 ◽  
Author(s):  
Kelly A. Miller ◽  
Madeline K. Sofia ◽  
Jacob W. A. Weaver ◽  
Christopher H. Seward ◽  
Michelle Dziejman
Keyword(s):  
Gene Expression ◽  
Cell Death ◽  
Vibrio Cholerae ◽  
Secretion System ◽  
Content Type ◽  
Transcriptional Regulatory ◽  
Type 3 Secretion System ◽  
Type 3

ABSTRACTGenes carried on the type 3 secretion system (T3SS) pathogenicity island ofVibrio choleraenon-O1/non-O139 serogroup strain AM-19226 must be precisely regulated in order for bacteria to cause disease. Previously reported results showed that both T3SS function and the presence of bile are required to cause Caco2-BBE cell cytotoxicity during coculture with strain AM-19226. We therefore investigated additional parameters affectingin vitrocell death, including bacterial load and the role of three transmembrane transcriptional regulatory proteins, VttRA, VttRB, and ToxR. VttRAand VttRBare encoded on the horizontally acquired T3SS genomic island, whereas ToxR is encoded on the ancestral chromosome. While strains carrying deletions in any one of the three transcriptional regulatory genes are unable to cause eukaryotic cell death, the results of complementation studies point to a hierarchy of regulatory control that converges onvttRBexpression. The data suggest both that ToxR and VttRAact upstream of VttRBand that modifying the level of eithervttRAorvttRBexpression can strongly influence T3SS gene expression. We therefore propose a model whereby T3SS activity and, hence,in vitrocytotoxicity are ultimately regulated byvttRBexpression.IMPORTANCEIn contrast to O1 and O139 serogroupV. choleraestrains that cause cholera using two main virulence factors (toxin-coregulated pilus [TCP] and cholera toxin [CT]), O39 serogroup strain AM-19226 uses a type 3 secretion system as its principal virulence mechanism. Although the regulatory network governing TCP and CT expression is well understood, the factors influencing T3SS-associated virulence are not. Using anin vitromammalian cell model to investigate the role of three ToxR-like transmembrane transcriptional activators in causing T3SS-dependent cytotoxicity, we found that expression levels and a hierarchical organization were important for promoting T3SS gene expression. Furthermore, our results suggest that horizontally acquired, ToxR-like proteins act in concert with the ancestral ToxR protein to orchestrate T3SS-mediated pathogenicity.

scholarly journals Francisella tularensis Live Vaccine Strain Folate Metabolism and Pseudouridine Synthase Gene Mutants Modulate Macrophage Caspase-1 Activation

2012 ◽  
Vol 81 (1) ◽  
pp. 201-208 ◽  
Author(s):  
Tyler K. Ulland ◽  
Ann M. Janowski ◽  
Blake W. Buchan ◽  
Matthew Faron ◽  
Suzanne L. Cassel ◽  
...  
Keyword(s):  
Francisella Tularensis ◽  
Vaccine Strain ◽  
Live Vaccine ◽  
Live Vaccine Strain ◽  
Wild Type ◽  
Content Type ◽  
Pseudouridine Synthase ◽  
Caspase 1

Francisella tularensisis a Gram-negative bacterium and the causative agent of the disease tularemia. Escape ofF. tularensisfrom the phagosome into the cytosol of the macrophage triggers the activation of the AIM2 inflammasome through a mechanism that is not well understood. Activation of the AIM2 inflammasome results in autocatalytic cleavage of caspase-1, resulting in the processing and secretion of interleukin-1β (IL-1β) and IL-18, which play a crucial role in innate immune responses toF. tularensis. We have identified the5-formyltetrahydrofolate cycloligasegene (FTL_0724) as being important forF. tularensislive vaccine strain (LVS) virulence. Infection of micein vivowith aF. tularensisLVSFTL_0724mutant resulted in diminished mortality compared to infection of mice with wild-type LVS. TheFTL_0724mutant also induced increased inflammasome-dependent IL-1β and IL-18 secretion and cytotoxicity in macrophagesin vitro. In contrast, infection of macrophages with aF. tularensisLVSrluD pseudouridine synthase(FTL_0699) mutant resulted in diminished IL-1β and IL-18 secretion from macrophagesin vitrocompared to infection of macrophages with wild-type LVS. In addition, theFTL_0699mutant was not attenuatedin vivo. These findings further illustrate thatF. tularensisLVS possesses numerous genes that influence its ability to activate the inflammasome, which is a key host strategy to control infection with this pathogenin vivo.

scholarly journals Differing Effects of Interleukin-10 on Cutaneous and Pulmonary Francisella tularensis Live Vaccine Strain Infection

2013 ◽  
Vol 81 (6) ◽  
pp. 2022-2027 ◽  
Author(s):  
Dennis W. Metzger ◽  
Sharon L. Salmon ◽  
Girish Kirimanjeswara
Keyword(s):  
Francisella Tularensis ◽  
Vaccine Strain ◽  
Pulmonary Infection ◽  
Interleukin 10 ◽  
Live Vaccine ◽  
Live Vaccine Strain ◽  
Content Type ◽  
Infectious Dose ◽  
Therapeutic Benefits

ABSTRACTWe investigated the role of interleukin-10 (IL-10) in cutaneous and pulmonary infection withFrancisella tularensis. We found that after intradermal challenge of mice with the live vaccine strain (LVS) ofF. tularensis, splenic IL-10 levels increased rapidly and reached a peak 5 days after infection. However, IL-10 expression after infection was detrimental, since IL-10−/−mice showed increased bacterial clearance and were resistant to an infectious dose (>106CFU/mouse) that was uniformly lethal for IL-10+/+mice. Furthermore, IL-10+/+mice treated with neutralizing anti-IL-10R monoclonal antibody were able to survive lethal cutaneous LVS challenge. The presence of IL-10 appeared to restrain the expression of IL-17, since high levels of splenic IL-17 were observed after intradermal LVS infection only in IL-10−/−mice. Furthermore, treatment with neutralizing anti-IL-17R antibody ablated the enhanced survival observed in IL-10−/−mice. However, neutralization of IL-10 activity in IL-17R−/−mice failed to provide protection. Thus, IL-10 suppresses a protective IL-17 response that is necessary for resistance to cutaneous LVS infection. Surprisingly, however, IL-10−/−mice were significantly more susceptible to pulmonary infection with LVS. Finally, although IL-10 is a critical and novel regulator of immunity toF. tularensisLVS infection, its effects were masked during infection with the highly virulent SchuS4 strain. Taken together, these findings suggest that differentially regulating expression of the IL-10 pathway in various tissues could ultimately have prophylactic and therapeutic benefits for protection against tularemia.

scholarly journals A New Mechanism for Ribosome Rescue Can Recruit RF1 or RF2 to Nonstop Ribosomes

mBio ◽  
2018 ◽  
Vol 9 (6) ◽  
Author(s):  
Tyler D. P. Goralski ◽  
Girish S. Kirimanjeswara ◽  
Kenneth C. Keiler
Keyword(s):  
Francisella Tularensis ◽  
Stop Codon ◽  
Intracellular Pathogen ◽  
Content Type ◽  
Main Pathway ◽  
Bioterrorism Agent ◽  
Hydrolysis Of ◽  
In Cells

ABSTRACTBacterial ribosomes frequently translate to the 3′ end of an mRNA without terminating at an in-frame stop codon. In all bacteria studied to date, these “nonstop” ribosomes are rescued usingtrans-translation. Genes required fortrans-translation are essential in some species, but other species can survive withouttrans-translation because they express an alternative ribosome rescue factor, ArfA or ArfB.Francisella tularensiscells lackingtrans-translation are viable, butF. tularensisdoes not encode ArfA or ArfB. Transposon mutagenesis followed by deep sequencing (Tn-seq) identified a new alternative ribosome rescue factor, now named ArfT.arfTcan be deleted in wild-type (wt) cells but not in cells that lacktrans-translation activity. Overexpression of ArfT suppresses the slow-growth phenotype in cells lackingtrans-translation and counteracts growth arrest caused bytrans-translation inhibitors, indicating that ArfT rescues nonstop ribosomesin vivo. Ribosome rescue assaysin vitroshow that ArfT promotes hydrolysis of peptidyl-tRNA on nonstop ribosomes in conjunction withF. tularensisrelease factors. Unlike ArfA, which requires RF2 for activity, ArfT can function with either RF1 or RF2. Overall, these results indicate that ArfT is a new alternative ribosome rescue factor with a distinct mechanism from ArfA and ArfB.IMPORTANCEFrancisella tularensisis a highly infectious intracellular pathogen that kills more than half of infected humans if left untreated.F. tularensishas also been classified as a potential bioterrorism agent with a great risk for deliberate misuse. Recently, compounds that inhibit ribosome rescue have been shown to have antibiotic activity againstF. tularensisand other important pathogens. Like all bacteria that have been studied,F. tularensisusestrans-translation as the main pathway to rescue stalled ribosomes. However, unlike most bacteria,F. tularensiscan survive without any of the known factors for ribosome rescue. Our work identified aF. tularensisprotein, ArfT, that rescues stalled ribosomes in the absence oftrans-translation using a new mechanism. These results indicate that ribosome rescue activity is essential inF. tularensisand suggest that ribosome rescue activity might be essential in all bacteria.

scholarly journals Needle-Free Delivery of Acetalated Dextran-Encapsulated AR-12 Protects Mice from Francisella tularensis Lethal Challenge

2016 ◽  
Vol 60 (4) ◽  
pp. 2052-2062 ◽  
Author(s):  
Ky V. Hoang ◽  
Heather Curry ◽  
Michael A. Collier ◽  
Hassan Borteh ◽  
Eric M. Bachelder ◽  
...  
Keyword(s):  
Francisella Tularensis ◽  
Lethal Challenge ◽  
Content Type ◽  
Human Macrophages ◽  
Gentamicin Treatment ◽  
Significant Toxicity ◽  
Serovar Typhimurium ◽  
Spectrum Activity

ABSTRACTFrancisella tularensiscauses tularemia and is a potential biothreat. Given the limited antibiotics for treating tularemia and the possible use of antibiotic-resistant strains as a biowarfare agent, new antibacterial agents are needed. AR-12 is an FDA-approved investigational new drug (IND) compound that induces autophagy and has shown host-directed, broad-spectrum activityin vitroagainstSalmonella entericaserovar Typhimurium andF. tularensis. We have shown that AR-12 encapsulated within acetalated dextran (Ace-DEX) microparticles (AR-12/MPs) significantly reduces host cell cytotoxicity compared to that with free AR-12, while retaining the ability to controlS.Typhimurium within infected human macrophages. In the present study, the toxicity and efficacy of AR-12/MPs in controlling virulent type AF. tularensisSchuS4 infection were examinedin vitroandin vivo. No significant toxicity of blank MPs or AR-12/MPs was observed in lung histology sections when the formulations were given intranasally to uninfected mice. In histology sections from the lungs of intranasally infected mice treated with the formulations, increased macrophage infiltration was observed for AR-12/MPs, with or without suboptimal gentamicin treatment, but not for blank MPs, soluble AR-12, or suboptimal gentamicin alone. AR-12/MPs dramatically reduced the burden ofF. tularensisin infected human macrophages, in a manner similar to that of free AR-12. However,in vivo, AR-12/MPs significantly enhanced the survival ofF. tularensisSchuS4-infected mice compared to that seen with free AR-12. In combination with suboptimal gentamicin treatment, AR-12/MPs further improved the survival ofF. tularensisSchuS4-infected mice. These studies provide support for Ace-DEX-encapsulated AR-12 as a promising new therapeutic agent for tularemia.

scholarly journals A Salmonella Virulence Factor Activates the NOD1/NOD2 Signaling Pathway

mBio ◽  
2011 ◽  
Vol 2 (6) ◽  
Author(s):  
A. Marijke Keestra ◽  
Maria G. Winter ◽  
Daisy Klein-Douwel ◽  
Mariana N. Xavier ◽  
Sebastian E. Winter ◽  
...  
Keyword(s):  
Signaling Pathway ◽  
Type Iii Secretion ◽  
Salmonella Enterica ◽  
Intestinal Inflammation ◽  
Inflammatory Responses ◽  
Type Iii Secretion System ◽  
Secretion System ◽  
Content Type ◽  
Type Iii

ABSTRACTThe invasion-associated type III secretion system (T3SS-1) ofSalmonella entericaserotype Typhimurium (S. Typhimurium) activates the transcription factor NF-κB in tissue culture cells and induces inflammatory responses in animal models through unknown mechanisms. Here we show that bacterial delivery or ectopic expression of SipA, a T3SS-1-translocated protein, led to the activation of the NOD1/NOD2 signaling pathway and consequent RIP2-mediated induction of NF-κB-dependent inflammatory responses. SipA-mediated activation of NOD1/NOD2 signaling was independent of bacterial invasionin vitrobut required an intact T3SS-1. In the mouse colitis model, SipA triggered mucosal inflammation in wild-type mice but not in NOD1/NOD2-deficient mice. These findings implicate SipA-driven activation of the NOD1/NOD2 signaling pathway as a mechanism by which the T3SS-1 induces inflammatory responsesin vitroandin vivo.IMPORTANCESalmonella entericaserotype Typhimurium (S. Typhimurium) deploys a type III secretion system (T3SS-1) to induce intestinal inflammation and benefits from the ensuing host response, which enhances growth of the pathogen in the intestinal lumen. However, the mechanisms by which the T3SS-1 triggers inflammatory responses have not been resolved. Here we show that the T3SS-1 effector protein SipA induces NF-κB activation and intestinal inflammation by activating the NOD1/NOD2 signaling pathway. These data suggest that the T3SS-1 escalates innate responses through a SipA-mediated activation of pattern recognition receptors in the host cell cytosol.

scholarly journals TolC-Dependent Modulation of Host Cell Death by the Francisella tularensis Live Vaccine Strain

2014 ◽  
Vol 82 (5) ◽  
pp. 2068-2078 ◽  
Author(s):  
Christopher R. Doyle ◽  
Ji-An Pan ◽  
Patricio Mena ◽  
Wei-Xing Zong ◽  
David G. Thanassi
Keyword(s):  
Cell Death ◽  
Immune Responses ◽  
Host Cell ◽  
Francisella Tularensis ◽  
Vaccine Strain ◽  
Live Vaccine ◽  
Live Vaccine Strain ◽  
Type I ◽  
Content Type ◽  
Host Cell Death

ABSTRACTFrancisella tularensisis a facultative intracellular, Gram-negative pathogen and the causative agent of tularemia. We previously identified TolC as a virulence factor of theF. tularensislive vaccine strain (LVS) and demonstrated that a ΔtolCmutant exhibits increased cytotoxicity toward host cells and elicits increased proinflammatory responses compared to those of the wild-type (WT) strain. TolC is the outer membrane channel component used by the type I secretion pathway to export toxins and other bacterial virulence factors. Here, we show that the LVS delays activation of the intrinsic apoptotic pathway in a TolC-dependent manner, both during infection of primary macrophages and during organ colonization in mice. The TolC-dependent delay in host cell death is required forF. tularensisto preserve its intracellular replicative niche. We demonstrate that TolC-mediated inhibition of apoptosis is an active process and not due to defects in the structural integrity of the ΔtolCmutant. These findings support a model wherein the immunomodulatory capacity ofF. tularensisrelies, at least in part, on TolC-secreted effectors. Finally, mice vaccinated with the ΔtolCLVS are protected from lethal challenge and clear challenge doses faster than WT-vaccinated mice, demonstrating that the altered host responses to primary infection with the ΔtolCmutant led to altered adaptive immune responses. Taken together, our data demonstrate that TolC is required for temporal modulation of host cell death during infection byF. tularensisand highlight how shifts in the magnitude and timing of host innate immune responses may lead to dramatic changes in the outcome of infection.

scholarly journals Intranasal Interleukin-12 Treatment for Protection against Respiratory Infection with the Francisella tularensis Live Vaccine Strain

2005 ◽  
Vol 73 (4) ◽  
pp. 2306-2311 ◽  
Author(s):  
Nathalie S. Duckett ◽  
Sofia Olmos ◽  
Douglas M. Durrant ◽  
Dennis W. Metzger
Keyword(s):  
Respiratory Infection ◽  
Francisella Tularensis ◽  
Vaccine Strain ◽  
Live Vaccine ◽  
Interleukin 12 ◽  
Live Vaccine Strain ◽  
Wild Type ◽  
Intranasal Infection ◽  
Ifn Γ

ABSTRACT Francisella tularensis is a gram-negative intracellular bacterium that can induce lethal respiratory infection in humans and rodents. However, little is known about the role of innate or adaptive immunity in protection from respiratory tularemia. In the present study, the role of interleukin-12 (IL-12) in inducing protective immunity in the lungs against intranasal infection of mice with the live vaccine strain (LVS) of F. tularensis was investigated. It was found that gamma interferon (IFN-γ) and IL-12 were strictly required for protection, since mice deficient in IFN-γ, IL-12 p35, or IL-12 p40 all succumbed to LVS doses that were sublethal for wild-type mice. Furthermore, exogenous IL-12 treatment 24 h before intranasal infection with a lethal dose of LVS (10,000 CFU) significantly decreased bacterial loads in the lungs, livers, and spleens of wild-type BALB/c and C57BL/6 mice and allowed the animals to survive infection; such protection was not observed in IFN-γ-deficient mice. The resistance induced by IL-12 to LVS infection was still observed in NK cell-deficient beige mice but not in CD8−/− mice. These results demonstrate that exogenous IL-12 delivered intranasally can prevent respiratory tularemia through a mechanism that is at least partially dependent upon the expression of IFN-γ and CD8 T cells.

scholarly journals Plasmodium falciparum Line-Dependent Association ofIn VitroGrowth-Inhibitory Activity and Risk of Malaria

2012 ◽  
Vol 80 (5) ◽  
pp. 1900-1908 ◽  
Author(s):  
Josea Rono ◽  
Anna Färnert ◽  
Daniel Olsson ◽  
Faith Osier ◽  
Ingegerd Rooth ◽  
...  
Keyword(s):  
Plasmodium Falciparum ◽  
Inhibitory Activity ◽  
Content Type ◽  
Phenotypic Differences ◽  
Erythrocyte Invasion ◽  
Growth Inhibitory ◽  
Growth Inhibitory Activity ◽  
Control Study

ABSTRACTPlasmodium falciparum's ability to invade erythrocytes is essential for its survival within the human host. Immune mechanisms that impair this ability are therefore expected to contribute to immunity against the parasite. Plasma of humans who are naturally exposed to malaria has been shown to have growth-inhibitory activity (GIA)in vitro. However, the importance of GIA in relation to protection from malaria has been unclear. In a case-control study nested within a longitudinally followed population in Tanzania, plasma samples collected at baseline from 171 individuals (55 cases and 116 age-matched controls) were assayed for GIA using threeP. falciparumlines (3D7, K1, and W2mef) chosen based on their erythrocyte invasion phenotypes. Distribution of GIA differed between the lines, with most samples inhibiting the growth of 3D7 and K1 and enhancing the growth of W2mef. GIA to 3D7 was associated with a reduced risk of malaria within 40 weeks of follow-up (odds ratio, 0.45; 95% confidence interval [CI], 0.21 to 0.96;P= 0.04), whereas GIA to K1 and W2mef was not. These results show that GIA, as well as its association with protection from malaria, is dependent on theP. falciparumline and can be explained by differences in erythrocyte invasion phenotypes between parasite lines. Our study contributes knowledge on the biological importance of growth inhibition and the potential influence ofP. falciparumerythrocyte invasion phenotypic differences on its relationship to protective immunity against malaria.

scholarly journals Activity of the Pore-Forming Virulence Factor Listeriolysin O Is Reversibly Inhibited by Naturally Occurring S-Glutathionylation

2017 ◽  
Vol 85 (4) ◽  
Author(s):  
Jonathan L. Portman ◽  
Qiongying Huang ◽  
Michelle L. Reniere ◽  
Anthony T. Iavarone ◽  
Daniel A. Portnoy
Keyword(s):  
Protein Function ◽  
Inhibitory Effect ◽  
Cysteine Residue ◽  
Infection Model ◽  
Listeriolysin O ◽  
Content Type ◽  
Pore Forming Proteins

ABSTRACT Cholesterol-dependent cytolysins (CDCs) represent a family of homologous pore-forming proteins secreted by many Gram-positive bacterial pathogens. CDCs mediate membrane binding partly through a conserved C-terminal undecapeptide, which contains a single cysteine residue. While mutational changes to other residues in the undecapeptide typically have severe effects, mutation of the cysteine residue to alanine has minor effects on overall protein function. Thus, the role of this highly conserved reactive cysteine residue remains largely unknown. We report here that the CDC listeriolysin O (LLO), secreted by the facultative intracellular pathogen Listeria monocytogenes, was posttranslationally modified by S-glutathionylation at this conserved cysteine residue and that either endogenously synthesized or exogenously added glutathione was sufficient to form this modification. When recapitulated with purified protein in vitro, this modification completely ablated the activity of LLO, and this inhibitory effect was fully reversible by treatment with reducing agents. A cysteine-to-alanine mutation in LLO rendered the protein completely resistant to inactivation by S-glutathionylation, and a mutant expressing this mutation retained full hemolytic activity. A mutant strain of L. monocytogenes expressing the cysteine-to-alanine variant of LLO was able to infect and replicate within bone marrow-derived macrophages indistinguishably from the wild type in vitro, yet it was attenuated 4- to 6-fold in a competitive murine infection model in vivo. This study suggests that S-glutathionylation may represent a mechanism by which CDC-family proteins are posttranslationally modified and regulated and help explain an evolutionary pressure to retain the highly conserved undecapeptide cysteine.

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