Expression of stm4467-encoded arginine deiminase controlled by the stm4463 regulator contributes to salmonella enterica serovar typhimurium virulence

Arginine deiminase (ADI), carbamate kinase (CK), and ornithine transcarbamoylase (OTC) constitute the ADI system. In addition to metabolic functions, the ADI system has been implicated in the virulence of certain pathogens. The pathogenic intracellular bacterium Salmonella enterica serovar Typhimurium possesses the STM4467, STM4466, and STM4465 genes, which are predicted to encode ADI, CK, and OTC, respectively. Here we report that the STM4467 gene encodes an ADI and that ADI activity plays a role in the successful infection of a mammalian host by S. Typhimurium. An STM4467 deletion mutant was defective for replication inside murine macrophages and was attenuated for virulence in mice. We determined that a regulatory protein encoded by the STM4463 gene functions as an activator for STM4467 expression. The expression of the ADI pathway genes was enhanced inside macrophages in a process that required STM4463. Lack of STM4463 impaired the ability of S. Typhimurium to replicate within macrophages. A mutant defective in STM4467-encoded ADI displayed normal production of nitric oxide by macrophages

LsrR-Mediated Quorum Sensing Controls Invasiveness of Salmonella typhimurium by Regulating SPI-1 and Flagella Genes

Bacterial cell-to-cell communication, termed quorum sensing (QS), controls bacterial behavior by using various signal molecules. Despite the fact that the LuxS/autoinducer-2 (AI-2) QS system is necessary for normal expression of Salmonella pathogenicity island-1 (SPI-1), the mechanism remains unknown. Here, we report that the LsrR protein, a transcriptional regulator known to be involved in LuxS/AI-2-mediated QS, is also associated with the regulation of SPI-1-mediated Salmonella virulence. We determined that LsrR negatively controls SPI-1 and flagella gene expressions. As phosphorylated AI-2 binds to and inactivates LsrR, LsrR remains active and decreases expression of SPI-1 and flagella genes in the luxS mutant. The reduced expression of those genes resulted in impaired invasion of Salmonella into epithelial cells. Expression of SPI-1 and flagella genes was also reduced by overexpression of the LsrR regulator from a plasmid, but was relieved by exogenous AI-2, which binds to and inactivates LsrR. These results imply that LsrR plays an important role in selecting infectious niche of Salmonella in QS dependent mode

Noncanonical Rab9a action supports retromer-mediated endosomal exit of human papillomavirus during virus entry.

Rab GTPases play key roles in controlling intracellular vesicular transport. GTP-bound Rab proteins support vesicle trafficking. Here, we report that, unlike cellular protein cargos, retromer-mediated delivery of human papillomaviruses (HPV) into the retrograde transport pathway during virus entry is inhibited by Rab9a in its GTP-bound form. Knockdown of Rab9a inhibits HPV entry by modulating the HPV-retromer interaction and impairing retromer-mediated endosome-to-Golgi transport of the incoming virus, resulting in the accumulation of HPV in the endosome. Rab9a is in proximity to HPV as early as 3.5 h post-infection, prior to the Rab7-HPV interaction, and HPV displays increased association with retromer in Rab9a knockdown cells, even in the presence of dominant negative Rab7. Thus, Rab9a can regulate HPV-retromer association independently of Rab7. Surprisingly, excess GTP-Rab9a impairs HPV entry, whereas excess GDP-Rab9a reduces association between L2 and Rab9a and stimulates entry. These findings reveal that HPV and cellular proteins utilize the Rab9a host trafficking machinery in distinct ways during intracellular trafficking

Implication of Quorum Sensing in Salmonella enterica Serovar Typhimurium Virulence: the luxS Gene Is Necessary for Expression of Genes in Pathogenicity Island 1▿

Despite the fact that the regulatory system sensing density of cell population and its signaling molecule have been identified in Salmonella enterica, the biological significance of this phenomenon termed as quorum sensing remains unknown. In this report, we provide evidence that the luxS gene is necessary for Salmonella virulence phenotypes. Transcription assays showed that the cell-density-dependent induction of the invF gene was abolished in a Salmonella strain with the luxS gene deleted. The effect of the luxS deletion was also investigated in other InvF-regulated genes expressed from Salmonella pathogenicity island 1 (SPI-1). The decreased expression of SPI-1 genes in the strain with luxS deleted could be restored by either the addition of a synthetic signal molecule or the introduction of a plasmid copy of the luxS gene. Thus, the reduced expression of invF and its regulated genes in Salmonella cells lacking quorum sensing resulted in the attenuation of virulence phenotypes both in vitro and in vivo

Elongation factor P controls translation of the mgtA gene encoding a Mg2+ transporter during Salmonella infection

Abstract Ribosome often stalls on mRNA sequences harboring consecutive proline codons. Elongation factor P (EF‐P) is required for the stalled ribosome to continue translation and thus the absence of EF‐P affects translation of the associated open reading frame. Here we report that EF‐P controls translation of the mgtA gene encoding a Mg2+‐transporting ATPase from the intracellualr pathogen Salmonella enterica serovar Typhimurium. EF‐P's effect on mgtA translation is dependent on the 550th and 551st proline codons in the coding region and thus substitution of those proline codons eliminates EF‐P‐mediated control of MgtA protein without affecting the Mg2+‐transporting activity of the mgtA gene. The Pro550 and Pro551‐substituted mgtA gene promotes Salmonella's intramacrophage survival and mouse virulence, suggesting that EF‐P‐mediated translational control of the mgtA gene is required for Salmonella pathogenesis

Programmed Delay of a Virulence Circuit Promotes Salmonella Pathogenicity

To accomplish successful infection, pathogens must operate their virulence programs in a precise, time-sensitive, and coordinated manner. A major question is how pathogens control the timing of virulence gene expression during infection. Here we report that the intracellular pathogen Salmonella controls the timing and level of virulence gene expression by using an inhibitory protein, EIIANtr. A DNA binding master virulence regulator, PhoP, controls various virulence genes inside acidic phagosomes. Salmonella decreases EIIANtr amounts at acidic pH in a Lon- and PhoP-dependent manner. This, in turn, promotes expression of the PhoP-activated virulence program because EIIANtr hampers activation of PhoP-regulated genes by interfering with PhoP binding to DNA. EIIANtr enables Salmonella to impede the activation of PhoP-regulated gene expression inside macrophages. Our findings suggest that Salmonella achieves programmed delay of virulence gene activation by adjusting levels of an inhibitory factor.Signal transduction systems dictate various cellular behaviors in response to environmental changes. To operate cellular programs appropriately, organisms have sophisticated regulatory factors to optimize the signal response. The PhoP/PhoQ master virulence regulatory system of the intracellular pathogen Salmonella enterica is activated inside acidic macrophage phagosomes. Here we report that Salmonella delays the activation of this system inside macrophages using an inhibitory protein, EIIANtr (a component of the nitrogen-metabolic phosphotransferase system). We establish that EIIANtr directly restrains PhoP binding to its target promoter, thereby negatively controlling the expression of PhoP-activated genes. PhoP furthers its activation by promoting Lon-mediated degradation of EIIANtr at acidic pH. These results suggest that Salmonella ensures robust activation of its virulence system by suspending the activation of PhoP until a sufficient level of active PhoP is present to overcome the inhibitory effect of EIIANtr. Our findings reveal how a pathogen precisely and efficiently operates its virulence program during infection

The overexpression of LsrR decreased <i>Salmonella</i> invasion into HEp-2 epithelial cells, even when the requirement for motility is bypassed through centrifugation.

<p>Monolayers of HEp-2 epithelial cells were infected with the wild-type (WT) <i>Salmonella</i>, WT harboring backbone plasmid, pUHE21-2<i>lacI^q</i>, and WT harboring pJH1 strains in the presence or absence of 100 µM IPTG. To exclude the requirement of motility, mild centrifugation was employed (centri.). The numbers of internalized bacteria were determined as described in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0037059#s4" target="_blank">Methods</a>. Values represent the relative amount of internalized bacteria and have been normalized to the level of internalization of WT strain, which was set at 1.00. Values are the average and standard deviation from three independent experiments, each done in triplicate.</p