Twin RNA Polymerase–Associated Proteins Control Virulence Gene Expression in Francisella tularensis

ABSTRACT Francisella tularensis is a highly infectious pathogen that infects animals and humans, causing tularemia. The ability to replicate within macrophages is central for virulence and relies on expression of genes located in the Francisella pathogenicity island (FPI), as well as expression of other genes. Regulation of FPI-encoded virulence gene expression in F. tularensis involves at least four regulatory proteins and is not fully understood. Here we studied the RNA-binding protein Hfq in F. tularensis and particularly the role that it plays as a global regulator of gene expression in stress tolerance and pathogenesis. We demonstrate that Hfq promotes resistance to several cellular stresses (including osmotic and membrane stresses). Furthermore, we show that Hfq is important for the ability of the F. tularensis vaccine strain LVS to induce disease and persist in organs of infected mice. We also demonstrate that Hfq is important for stress tolerance and full virulence in a virulent clinical isolate of F. tularensis, FSC200. Finally, microarray analyses revealed that Hfq regulates expression of numerous genes, including genes located in the FPI. Strikingly, Hfq negatively regulates only one of two divergently expressed putative operons in the FPI, in contrast to the other known regulators, which regulate the entire FPI. Hfq thus appears to be a new pleiotropic regulator of virulence in F. tularensis, acting mostly as a repressor, in contrast to the other regulators identified so far. Moreover, the results obtained suggest a novel regulatory mechanism for a subset of FPI genes.

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The Emerging Role for RNA Polymerase II in Regulating Virulence Gene Expression in Malaria Parasites

PLoS Pathogens ◽

10.1371/journal.ppat.1004926 ◽

2015 ◽

Vol 11 (7) ◽

pp. e1004926 ◽

Cited By ~ 4

Author(s):

Uchechi E. Ukaegbu ◽

Kirk W. Deitsch

Keyword(s):

Gene Expression ◽

Rna Polymerase ◽

Rna Polymerase Ii ◽

Virulence Gene ◽

Malaria Parasites ◽

Virulence Gene Expression

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Polyphosphate Kinase Antagonizes Virulence Gene Expression inFrancisella tularensis

Journal of Bacteriology ◽

10.1128/jb.00460-17 ◽

2017 ◽

Vol 200 (3) ◽

Cited By ~ 1

Author(s):

Amy E. Rohlfing ◽

Kathryn M. Ramsey ◽

Simon L. Dove

Keyword(s):

Gene Expression ◽

Rna Polymerase ◽

Virulence Genes ◽

Virulence Gene ◽

Dna Binding Protein ◽

Polyphosphate Kinase ◽

Prior Work ◽

Content Type ◽

Virulence Gene Expression ◽

Regulatory Effects

ABSTRACTThe alarmone ppGpp is a critical regulator of virulence gene expression inFrancisella tularensis. In this intracellular pathogen, ppGpp is thought to work in concert with the putative DNA-binding protein PigR and the SspA protein family members MglA and SspA to control a common set of genes. MglA and SspA form a complex that interacts with RNA polymerase (RNAP), and PigR functions by interacting with the RNAP-associated MglA-SspA complex. Prior work suggested that ppGpp indirectly exerts its regulatory effects inF. tularensisby promoting the accumulation of polyphosphate in the cell, which in turn was required for formation of the MglA-SspA complex. Here we show that inEscherichia coli, neither polyphosphate nor ppGpp is required for formation of the MglA-SspA complex but that ppGpp promotes the interaction between PigR and the MglA-SspA complex. Moreover, we show that polyphosphate kinase, the enzyme responsible for the synthesis of polyphosphate, antagonizes virulence gene expression inF. tularensis, a finding that is inconsistent with the notion that polyphosphate accumulation promotes virulence gene expression in this organism. Our findings identify polyphosphate kinase as a novel negative regulator of virulence gene expression inF. tularensisand support a model in which ppGpp exerts its positive regulatory effects by promoting the interaction between PigR and the MglA-SspA complex.IMPORTANCEInFrancisella tularensis, MglA and SspA form a complex that associates with RNA polymerase to positively control the expression of key virulence genes. The MglA-SspA complex works together with the putative DNA-binding protein PigR and the alarmone ppGpp. PigR functions by interacting directly with the MglA-SspA complex, but how ppGpp exerts its effects was unclear. Prior work indicated that ppGpp acts by promoting the accumulation of polyphosphate, which is required for MglA and SspA to interact. Here we show that formation of the MglA-SspA complex does not require polyphosphate. Furthermore, we find that polyphosphate antagonizes the expression of virulence genes inF. tularensis. Thus, ppGpp does not promote virulence gene expression in this organism through an effect on polyphosphate.

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Vibrio harveyi virulence gene expression in vitro and in vivo during infection in black tiger shrimp Penaeus monodon

Diseases of Aquatic Organisms ◽

10.3354/dao03475 ◽

2020 ◽

Vol 139 ◽

pp. 153-160

Author(s):

S Peeralil ◽

TC Joseph ◽

V Murugadas ◽

PG Akhilnath ◽

VN Sreejith ◽

...

Keyword(s):

Gene Expression ◽

Virulence Genes ◽

Vibrio Harveyi ◽

Penaeus Monodon ◽

Challenge Test ◽

Virulence Gene ◽

Economic Losses ◽

Virulence Gene Expression

Luminescent Vibrio harveyi is common in sea and estuarine waters. It produces several virulence factors and negatively affects larval penaeid shrimp in hatcheries, resulting in severe economic losses to shrimp aquaculture. Although V. harveyi is an important pathogen of shrimp, its pathogenicity mechanisms have yet to be completely elucidated. In the present study, isolates of V. harveyi were isolated and characterized from diseased Penaeus monodon postlarvae from hatcheries in Kerala, India, from September to December 2016. All 23 tested isolates were positive for lipase, phospholipase, caseinase, gelatinase and chitinase activity, and 3 of the isolates (MFB32, MFB71 and MFB68) showed potential for significant biofilm formation. Based on the presence of virulence genes, the isolates of V. harveyi were grouped into 6 genotypes, predominated by vhpA+ flaB+ ser+ vhh1- luxR+ vopD- vcrD+ vscN-. One isolate from each genotype was randomly selected for in vivo virulence experiments, and the LD50 ranged from 1.7 ± 0.5 × 103 to 4.1 ± 0.1 × 105 CFU ml-1. The expression of genes during the infection in postlarvae was high in 2 of the isolates (MFB12 and MFB32), consistent with the result of the challenge test. However, in MFB19, even though all genes tested were present, their expression level was very low and likely contributed to its lack of virulence. Because of the significant variation in gene expression, the presence of virulence genes alone cannot be used as a marker for pathogenicity of V. harveyi.

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