1
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Bruna RE, Kendra CG, Pontes MH. Phosphorus starvation response and PhoB-independent utilization of organic phosphate sources by Salmonella enterica. Microbiol Spectr 2023; 11:e0226023. [PMID: 37787565 PMCID: PMC10715179 DOI: 10.1128/spectrum.02260-23] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2023] [Accepted: 08/21/2023] [Indexed: 10/04/2023] Open
Abstract
IMPORTANCE Phosphorus (P) is the fifth most abundant element in living cells. This element is acquired mainly as inorganic phosphate (Pi, PO4 3-). In enteric bacteria, P starvation activates a two-component signal transduction system which is composed of the membrane sensor protein PhoR and its cognate transcription regulator PhoB. PhoB, in turn, promotes the transcription of genes that help maintain Pi homeostasis. Here, we characterize the P starvation response of the bacterium Salmonella enterica. We determine the PhoB-dependent and independent transcriptional changes promoted by P starvation and identify proteins enabling the utilization of a range of organic substrates as sole P sources. We show that transcription and activity of a subset of these proteins are independent of PhoB and Pi availability. These results establish that Salmonella enterica can maintain Pi homeostasis and repress PhoB/PhoR activation even when cells are grown in medium lacking Pi.
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Affiliation(s)
- Roberto E. Bruna
- Department of Pathology and Laboratory Medicine, Pennsylvania State University College of Medicine, Hershey, Pennsylvania, USA
- The One Health Microbiome Center, Huck Institute of the Life Sciences, Pennsylvania State University, University Park, Pennsylvania, USA
| | - Christopher G. Kendra
- Department of Pathology and Laboratory Medicine, Pennsylvania State University College of Medicine, Hershey, Pennsylvania, USA
- The One Health Microbiome Center, Huck Institute of the Life Sciences, Pennsylvania State University, University Park, Pennsylvania, USA
| | - Mauricio H. Pontes
- Department of Pathology and Laboratory Medicine, Pennsylvania State University College of Medicine, Hershey, Pennsylvania, USA
- The One Health Microbiome Center, Huck Institute of the Life Sciences, Pennsylvania State University, University Park, Pennsylvania, USA
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2
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Ciolli Mattioli C, Eisner K, Rosenbaum A, Wang M, Rivalta A, Amir A, Golding I, Avraham R. Physiological stress drives the emergence of a Salmonella subpopulation through ribosomal RNA regulation. Curr Biol 2023; 33:4880-4892.e14. [PMID: 37879333 PMCID: PMC10843543 DOI: 10.1016/j.cub.2023.09.064] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2023] [Revised: 08/24/2023] [Accepted: 09/26/2023] [Indexed: 10/27/2023]
Abstract
Bacteria undergo cycles of growth and starvation to which they must adapt swiftly. One important strategy for adjusting growth rates relies on ribosomal levels. Although high ribosomal levels are required for fast growth, their dynamics during starvation remain unclear. Here, we analyzed ribosomal RNA (rRNA) content of individual Salmonella cells by using fluorescence in situ hybridization (rRNA-FISH) and measured a dramatic decrease in rRNA numbers only in a subpopulation during nutrient limitation, resulting in a bimodal distribution of cells with high and low rRNA content. During nutritional upshifts, the two subpopulations were associated with distinct phenotypes. Using a transposon screen coupled with rRNA-FISH, we identified two mutants, DksA and RNase I, acting on rRNA transcription shutdown and degradation, which abolished the formation of the subpopulation with low rRNA content. Our work identifies a bacterial mechanism for regulation of ribosomal bimodality that may be beneficial for population survival during starvation.
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Affiliation(s)
- Camilla Ciolli Mattioli
- Department of Immunology and Regenerative Biology, Weizmann Institute of Science, Rehovot 7610001, Israel
| | - Kfir Eisner
- Department of Physics of Complex Systems, Weizmann Institute of Science, Rehovot 7610001, Israel
| | - Aviel Rosenbaum
- Department of Immunology and Regenerative Biology, Weizmann Institute of Science, Rehovot 7610001, Israel
| | - Mengyu Wang
- Department of Physics, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
| | - Andre' Rivalta
- Department of Chemical and Structural Biology, Weizmann Institute of Science, Rehovot 7610001, Israel
| | - Ariel Amir
- Department of Physics of Complex Systems, Weizmann Institute of Science, Rehovot 7610001, Israel
| | - Ido Golding
- Department of Physics, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
| | - Roi Avraham
- Department of Immunology and Regenerative Biology, Weizmann Institute of Science, Rehovot 7610001, Israel.
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3
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Bruna RE, Kendra CG, Pontes MH. An intracellular phosphorus-starvation signal activates the PhoB/PhoR two-component system in Salmonella enterica. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.03.23.533958. [PMID: 36993483 PMCID: PMC10055408 DOI: 10.1101/2023.03.23.533958] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 03/31/2023]
Abstract
Bacteria acquire P primarily as inorganic orthophosphate (Pi, PO43-). Once internalized, Pi is rapidly assimilated into biomass during the synthesis of ATP. Because Pi is essential, but excessive ATP is toxic, the acquisition of environmental Pi is tightly regulated. In the bacterium Salmonella enterica (Salmonella), growth in Pi-limiting environments activates the membrane sensor histidine kinase PhoR, leading to the phosphorylation of its cognate transcriptional regulator PhoB and subsequent transcription of genes involved in adaptations to low Pi. Pi limitation is thought to promote PhoR kinase activity by altering the conformation of a membrane signaling complex comprised by PhoR, the multicomponent Pi transporter system PstSACB and the regulatory protein PhoU. However, the identity of the low Pi signal and how it controls PhoR activity remain unknown. Here we characterize the PhoB-dependent and independent transcriptional changes elicited by Salmonella in response to P starvation, and identify PhoB-independent genes that are required for the utilization of several organic-P sources. We use this knowledge to identify the cellular compartment where the PhoR signaling complex senses the Pi-limiting signal. We demonstrate that the PhoB and PhoR signal transduction proteins can be maintained in an inactive state even when Salmonella is grown in media lacking Pi. Our results establish that PhoR activity is controlled by an intracellular signal resulting from P insufficiency.
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Affiliation(s)
- Roberto E. Bruna
- Department of Pathology and Laboratory Medicine, Pennsylvania State College of Medicine, Hershey, PA 17033, United States of America
| | - Christopher G. Kendra
- Department of Pathology and Laboratory Medicine, Pennsylvania State College of Medicine, Hershey, PA 17033, United States of America
| | - Mauricio H. Pontes
- Department of Pathology and Laboratory Medicine, Pennsylvania State College of Medicine, Hershey, PA 17033, United States of America
- Department of Microbiology and Immunology, Pennsylvania State College of Medicine, Hershey, PA 17033, United States of America
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4
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Aljghami ME, Barghash MM, Majaesic E, Bhandari V, Houry WA. Cellular functions of the ClpP protease impacting bacterial virulence. Front Mol Biosci 2022; 9:1054408. [PMID: 36533084 PMCID: PMC9753991 DOI: 10.3389/fmolb.2022.1054408] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2022] [Accepted: 11/15/2022] [Indexed: 09/28/2023] Open
Abstract
Proteostasis mechanisms significantly contribute to the sculpting of the proteomes of all living organisms. ClpXP is a central AAA+ chaperone-protease complex present in both prokaryotes and eukaryotes that facilitates the unfolding and subsequent degradation of target substrates. ClpX is a hexameric unfoldase ATPase, while ClpP is a tetradecameric serine protease. Substrates of ClpXP belong to many cellular pathways such as DNA damage response, metabolism, and transcriptional regulation. Crucially, disruption of this proteolytic complex in microbes has been shown to impact the virulence and infectivity of various human pathogenic bacteria. Loss of ClpXP impacts stress responses, biofilm formation, and virulence effector protein production, leading to decreased pathogenicity in cell and animal infection models. Here, we provide an overview of the multiple critical functions of ClpXP and its substrates that modulate bacterial virulence with examples from several important human pathogens.
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Affiliation(s)
- Mazen E. Aljghami
- Department of Biochemistry, University of Toronto, Toronto, ON, Canada
| | - Marim M. Barghash
- Department of Biochemistry, University of Toronto, Toronto, ON, Canada
| | - Emily Majaesic
- Department of Chemistry, University of Toronto, Toronto, ON, Canada
| | - Vaibhav Bhandari
- Department of Biochemistry, University of Toronto, Toronto, ON, Canada
| | - Walid A. Houry
- Department of Biochemistry, University of Toronto, Toronto, ON, Canada
- Department of Chemistry, University of Toronto, Toronto, ON, Canada
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5
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Role of RpoS in Regulating Stationary Phase Salmonella Typhimurium Pathogenesis-Related Stress Responses under Physiological Low Fluid Shear Force Conditions. mSphere 2022; 7:e0021022. [PMID: 35913142 PMCID: PMC9429890 DOI: 10.1128/msphere.00210-22] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
The discovery that biomechanical forces regulate microbial virulence was established with the finding that physiological low fluid shear (LFS) forces altered gene expression, stress responses, and virulence of the enteric pathogen Salmonella enterica serovar Typhimurium during the log phase. These log phase LFS-induced phenotypes were independent of the master stress response regulator, RpoS (σS). Given the central importance of RpoS in regulating stationary-phase stress responses of S. Typhimurium cultured under conventional shake flask and static conditions, we examined its role in stationary-phase cultures grown under physiological LFS. We constructed an isogenic rpoS mutant derivative of wild-type S. Typhimurium and compared the ability of these strains to survive in vitro pathogenesis-related stresses that mimic those encountered in the infected host and environment. We also compared the ability of these strains to colonize (adhere, invade, and survive within) human intestinal epithelial cell cultures. Unexpectedly, LFS-induced resistance of stationary-phase S. Typhimurium cultures to acid and bile salts stresses did not rely on RpoS. Likewise, RpoS was dispensable for stationary-phase LFS cultures to adhere to and survive within intestinal epithelial cells. In contrast, the resistance of these cultures to challenges of oxidative and thermal stresses, and their invasion into intestinal epithelial cells was influenced by RpoS. These findings expand our mechanistic understanding of how physiological fluid shear forces modulate stationary-phase S. Typhimurium physiology in unexpected ways and provide clues into microbial mechanobiology and nuances of Salmonella responses to microenvironmental niches in the infected host. IMPORTANCE Bacterial pathogens respond dynamically to a variety of stresses in the infected host, including physical forces of fluid flow (fluid shear) across their surfaces. While pathogens experience wide fluctuations in fluid shear during infection, little is known about how these forces regulate microbial pathogenesis. This is especially important for stationary-phase bacterial growth, which is a critical period to understand microbial resistance, survival, and infection potential, and is regulated in many bacteria by the general stationary-phase stress response protein RpoS. Here, we showed that, unlike conventional culture conditions, several stationary-phase Salmonella pathogenic stress responses were not impacted by RpoS when bacteria were cultured under fluid shear conditions relevant to those encountered in the intestine of the infected host. These findings offer new insight into how physiological fluid shear forces encountered by Salmonella during infection might impact pathogenic responses in unexpected ways that are relevant to their disease-causing ability.
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6
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Kim JS, Liu L, Davenport B, Kant S, Morrison TE, Vazquez-Torres A. Oxidative stress activates transcription of Salmonella pathogenicity island-2 genes in macrophages. J Biol Chem 2022; 298:102130. [PMID: 35714768 PMCID: PMC9270255 DOI: 10.1016/j.jbc.2022.102130] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2022] [Revised: 06/06/2022] [Accepted: 06/08/2022] [Indexed: 11/30/2022] Open
Abstract
The type III secretion system encoded in the Salmonella pathogenicity island-2 (SPI-2) gene cluster facilitates intracellular growth of nontyphoidal Salmonella by interfering with the maturation of Salmonella-containing vacuoles along the degradative pathway. SPI-2 gene products also protect Salmonella against the antimicrobial activity of reactive oxygen species (ROS) synthesized by the phagocyte NADPH oxidase 2 (NOX2). However, a potential relationship between inflammatory ROS and the activation of transcription of SPI-2 genes by intracellular Salmonella is unclear. Here, we show that ROS engendered in the innate host response stimulate SPI-2 gene transcription. We found that the expression of SPI-2 genes in Salmonella-sustaining oxidative stress conditions involves DksA, a protein otherwise known to regulate the stringent response of bacteria to nutritional stress. We also demonstrate that the J and zinc-2-oxidoreductase domains of DnaJ as well as the ATPase activity of the DnaK chaperone facilitate loading of DksA onto RNA polymerase complexed with SPI-2 promoters. Furthermore, the DksA-driven transcription of SPI-2 genes in Salmonella experiencing oxidative stress is contingent on upstream OmpR, PhoP, and SsrB signaling events that participate in the removal of nucleoid proteins while simultaneously recruiting RNA polymerase to SPI-2 promoter regions. Taken together, our results suggest the activation of SPI-2 gene transcription in Salmonella subjected to ROS produced by the respiratory burst of macrophages protects this intracellular pathogen against NOX2-mediated killing. We propose that Salmonella have co-opted inflammatory ROS to induce SPI-2-mediated protective responses against NOX2 host defenses.
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Affiliation(s)
- Ju-Sim Kim
- University of Colorado School of Medicine, Department of Immunology & Microbiology, Aurora, Colorado, USA
| | - Lin Liu
- University of Colorado School of Medicine, Department of Immunology & Microbiology, Aurora, Colorado, USA
| | - Bennett Davenport
- University of Colorado School of Medicine, Department of Immunology & Microbiology, Aurora, Colorado, USA
| | - Sashi Kant
- University of Colorado School of Medicine, Department of Immunology & Microbiology, Aurora, Colorado, USA
| | - Thomas E Morrison
- University of Colorado School of Medicine, Department of Immunology & Microbiology, Aurora, Colorado, USA
| | - Andres Vazquez-Torres
- University of Colorado School of Medicine, Department of Immunology & Microbiology, Aurora, Colorado, USA; Veterans Affairs Eastern Colorado Health Care System, Denver, Colorado, USA.
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7
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Niu L, Zhang Y, Jie M, Cheng Y, Xiang Q, Zhang Z, Bai Y. Synergetic effect of
petit
‐high pressure carbon dioxide combined with cinnamon (
Cinnamomum cassia
) essential oil against
Salmonella typhimurium. Int J Food Sci Technol 2022. [DOI: 10.1111/ijfs.15613] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Affiliation(s)
- Liyuan Niu
- College of Food and Bioengineering Zhengzhou University of Light Industry Zhengzhou China
- Henan Key Laboratory of Cold Chain Food Quality and Safety Control Zhengzhou China
- Collaborative Innovation Center of Food Production and Safety Henan Province Zhengzhou China
| | - Yilin Zhang
- College of Food and Bioengineering Zhengzhou University of Light Industry Zhengzhou China
| | - Mingsha Jie
- College of Food and Bioengineering Zhengzhou University of Light Industry Zhengzhou China
- Henan Key Laboratory of Cold Chain Food Quality and Safety Control Zhengzhou China
- Collaborative Innovation Center of Food Production and Safety Henan Province Zhengzhou China
| | - Yingxin Cheng
- College of Food and Bioengineering Zhengzhou University of Light Industry Zhengzhou China
| | - Qisen Xiang
- College of Food and Bioengineering Zhengzhou University of Light Industry Zhengzhou China
- Henan Key Laboratory of Cold Chain Food Quality and Safety Control Zhengzhou China
- Collaborative Innovation Center of Food Production and Safety Henan Province Zhengzhou China
| | - Zhijian Zhang
- College of Food and Bioengineering Zhengzhou University of Light Industry Zhengzhou China
- Henan Key Laboratory of Cold Chain Food Quality and Safety Control Zhengzhou China
- Collaborative Innovation Center of Food Production and Safety Henan Province Zhengzhou China
| | - Yanhong Bai
- College of Food and Bioengineering Zhengzhou University of Light Industry Zhengzhou China
- Henan Key Laboratory of Cold Chain Food Quality and Safety Control Zhengzhou China
- Collaborative Innovation Center of Food Production and Safety Henan Province Zhengzhou China
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8
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Guillén S, Marcén M, Fau E, Mañas P, Cebrián G. Relationship between growth ability, virulence, and resistance to food-processing related stresses in non-typhoidal Salmonellae. Int J Food Microbiol 2022; 361:109462. [PMID: 34749188 DOI: 10.1016/j.ijfoodmicro.2021.109462] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2021] [Revised: 10/01/2021] [Accepted: 10/25/2021] [Indexed: 11/29/2022]
Abstract
The ability of Salmonella to resist and adapt to harsh conditions is one of the major features that have made this microorganism such a relevant health hazard. However, the impact of these resistance responses on other aspects of Salmonella physiology, such as virulence and growth ability, is still not fully understood. The objective of this study was to determine the maximum growth rates (in three different media), virulence (adhesion and invasion of Caco-2 cells), and other phenotypic characteristics (biofilm-forming ability and antimicrobial resistance) of 23 Salmonella strains belonging to different serovars, and to compare them with their previously determined stress resistance parameters. Significant differences (p < 0.05) in growth rates, virulence, and biofilm-forming ability were found among the 23 strains studied. Nevertheless, whereas less than 3-fold change between the lowest and the highest growth rate was observed, the percentage of cells capable of invading Caco-2 cells varied more than 100-fold, that to form biofilms more than 30-fold, and the antibiotic MICs varied up to 512-fold, among the different strains. Results indicate that those strains with the highest cell adhesion ability were not always the most invasive ones and suggest that, in general terms, a higher stress resistance did not imply a reduced growth ability (rate). Similarly, no association between stress resistance and biofilm formation ability (except for acid stress) or antibiotic resistance (with minor exceptions) was found. Our data also suggest that, in Salmonella, acid stress resistance would be associated with virulence, since a positive correlation of that trait with adhesion and a negative correlation with invasion was found. This study contributes to a better understanding of the physiology of Salmonella and the relationship between bacterial stress resistance, growth ability, and virulence. It also provides new data regarding intra-specific variability of a series of phenotypic characteristics of Salmonella that are relevant from the food safety perspective.
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Affiliation(s)
- Silvia Guillén
- Departamento de Producción Animal y Ciencia de los Alimentos, Facultad de Veterinaria, Instituto Agroalimentario de Aragón - IA2 - (Universidad de Zaragoza-CITA), Zaragoza, Spain
| | - María Marcén
- Departamento de Producción Animal y Ciencia de los Alimentos, Facultad de Veterinaria, Instituto Agroalimentario de Aragón - IA2 - (Universidad de Zaragoza-CITA), Zaragoza, Spain
| | - Ester Fau
- Departamento de Producción Animal y Ciencia de los Alimentos, Facultad de Veterinaria, Instituto Agroalimentario de Aragón - IA2 - (Universidad de Zaragoza-CITA), Zaragoza, Spain
| | - Pilar Mañas
- Departamento de Producción Animal y Ciencia de los Alimentos, Facultad de Veterinaria, Instituto Agroalimentario de Aragón - IA2 - (Universidad de Zaragoza-CITA), Zaragoza, Spain
| | - Guillermo Cebrián
- Departamento de Producción Animal y Ciencia de los Alimentos, Facultad de Veterinaria, Instituto Agroalimentario de Aragón - IA2 - (Universidad de Zaragoza-CITA), Zaragoza, Spain.
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9
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Kim SI, Kim E, Yoon H. σ S-Mediated Stress Response Induced by Outer Membrane Perturbation Dampens Virulence in Salmonella enterica serovar Typhimurium. Front Microbiol 2021; 12:750940. [PMID: 34659184 PMCID: PMC8516096 DOI: 10.3389/fmicb.2021.750940] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2021] [Accepted: 08/30/2021] [Indexed: 12/13/2022] Open
Abstract
Salmonella alters cellular processes as a strategy to improve its intracellular fitness during host infection. Alternative σ factors are known to rewire cellular transcriptional regulation in response to environmental stressors. σs factor encoded by the rpoS gene is a key regulator required for eliciting the general stress response in many proteobacteria. In this study, Salmonella Typhimurium deprived of an outer membrane protein YcfR was attenuated in intracellular survival and exhibited downregulation in Salmonella pathogenicity island-2 (SPI-2) genes. This decreased SPI-2 expression caused by the outer membrane perturbation was abolished in the absence of rpoS. Interestingly, regardless of the defects in the outer membrane integrity, RpoS overproduction decreased transcription from the common promoter of ssrA and ssrB, which encode a two-component regulatory system for SPI-2. RpoS was found to compete with RpoD for binding to the PssrA region, and its binding activity with RNA polymerase (RNAP) to form Eσs holoenzyme was stimulated by the small regulatory protein Crl. This study demonstrates that Salmonella undergoing RpoS-associated stress responses due to impaired envelope integrity may reciprocally downregulate the expression of SPI-2 genes to reduce its virulence.
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Affiliation(s)
- Seul I Kim
- Department of Molecular Science and Technology, Ajou University, Suwon, South Korea
| | - Eunsuk Kim
- Department of Molecular Science and Technology, Ajou University, Suwon, South Korea
| | - Hyunjin Yoon
- Department of Molecular Science and Technology, Ajou University, Suwon, South Korea.,Department of Applied Chemistry and Biological Engineering, Ajou University, Suwon, South Korea
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10
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Impact of the Resistance Responses to Stress Conditions Encountered in Food and Food Processing Environments on the Virulence and Growth Fitness of Non-Typhoidal Salmonellae. Foods 2021; 10:foods10030617. [PMID: 33799446 PMCID: PMC8001757 DOI: 10.3390/foods10030617] [Citation(s) in RCA: 20] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2021] [Revised: 02/24/2021] [Accepted: 03/10/2021] [Indexed: 01/22/2023] Open
Abstract
The success of Salmonella as a foodborne pathogen can probably be attributed to two major features: its remarkable genetic diversity and its extraordinary ability to adapt. Salmonella cells can survive in harsh environments, successfully compete for nutrients, and cause disease once inside the host. Furthermore, they are capable of rapidly reprogramming their metabolism, evolving in a short time from a stress-resistance mode to a growth or virulent mode, or even to express stress resistance and virulence factors at the same time if needed, thanks to a complex and fine-tuned regulatory network. It is nevertheless generally acknowledged that the development of stress resistance usually has a fitness cost for bacterial cells and that induction of stress resistance responses to certain agents can trigger changes in Salmonella virulence. In this review, we summarize and discuss current knowledge concerning the effects that the development of resistance responses to stress conditions encountered in food and food processing environments (including acid, osmotic and oxidative stress, starvation, modified atmospheres, detergents and disinfectants, chilling, heat, and non-thermal technologies) exerts on different aspects of the physiology of non-typhoidal Salmonellae, with special emphasis on virulence and growth fitness.
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11
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Kolenda R, Burdukiewicz M, Wimonć M, Aleksandrowicz A, Ali A, Szabo I, Tedin K, Bartholdson Scott J, Pickard D, Schierack P. Identification of Natural Mutations Responsible for Altered Infection Phenotypes of Salmonella enterica Clinical Isolates by Using Cell Line Infection Screens. Appl Environ Microbiol 2021; 87:e02177-20. [PMID: 33127819 PMCID: PMC7783345 DOI: 10.1128/aem.02177-20] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2020] [Accepted: 10/22/2020] [Indexed: 12/18/2022] Open
Abstract
The initial steps of Salmonella pathogenesis involve adhesion to and invasion into host epithelial cells. While well-studied for Salmonella enterica serovar Typhimurium, the factors contributing to this process in other, host-adapted serovars remains unexplored. Here, we screened clinical isolates of serovars Gallinarum, Dublin, Choleraesuis, Typhimurium, and Enteritidis for adhesion to and invasion into intestinal epithelial cell lines of human, porcine, and chicken origins. Thirty isolates with altered infectivity were used for genomic analyses, and 14 genes and novel mutations associated with high or low infectivity were identified. The functions of candidate genes included virulence gene expression regulation and cell wall or membrane synthesis and components. The role of several of these genes in Salmonella adhesion to and invasion into cells has not previously been investigated. The genes dksA (encoding a stringent response regulator) and sanA (encoding a vancomycin high-temperature exclusion protein) were selected for further analyses, and we confirmed their roles in adhesion to and invasion into host cells. Furthermore, transcriptomic analyses were performed for S Enteritidis and S Typhimurium, with two highly infective and two marginally infective isolates for each serovar. Expression profiles for the isolates with altered infection phenotypes revealed the importance of type 3 secretion system expression levels in the determination of an isolate's infection phenotype. Taken together, these data indicate a new role in cell host infection for genes or gene variants previously not associated with adhesion to and invasion into the epithelial cells.IMPORTANCESalmonella is a foodborne pathogen affecting over 200 million people and resulting in over 200,000 fatal cases per year. Its adhesion to and invasion into intestinal epithelial cells represent one of the first and key steps in the pathogenesis of salmonellosis. Still, around 35 to 40% of bacterial genes have no experimentally validated function, and their contribution to bacterial virulence, including adhesion and invasion, remains largely unknown. Therefore, the significance of this study is in the identification of new genes or gene allelic variants previously not associated with adhesion and invasion. It is well established that blocking adhesion and/or invasion would stop or hamper bacterial infection; therefore, the new findings from this study could be used in future developments of anti-Salmonella therapy targeting genes involved in these key processes. Such treatment could be a valuable alternative, as the prevalence of antibiotic-resistant bacteria is increasing very rapidly.
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Affiliation(s)
- Rafał Kolenda
- Department of Biochemistry and Molecular Biology, Faculty of Veterinary Medicine, Wrocław University of Environmental and Life Sciences, Wrocław, Poland
- Institute of Biotechnology, Faculty Environment and Natural Sciences, BTU Cottbus-Senftenberg, Senftenberg, Germany
| | | | - Marcjanna Wimonć
- Department of Biochemistry and Molecular Biology, Faculty of Veterinary Medicine, Wrocław University of Environmental and Life Sciences, Wrocław, Poland
| | - Adrianna Aleksandrowicz
- Department of Biochemistry and Molecular Biology, Faculty of Veterinary Medicine, Wrocław University of Environmental and Life Sciences, Wrocław, Poland
| | - Aamir Ali
- National Institute for Biotechnology and Genetic Engineering, Faisalabad, Pakistan
| | - Istvan Szabo
- National Salmonella Reference Laboratory, German Federal Institute for Risk Assessment (BfR), Berlin, Germany
| | | | - Josefin Bartholdson Scott
- Cambridge Institute for Therapeutic Immunology & Infectious Disease, University of Cambridge Department of Medicine, Cambridge, United Kingdom
| | - Derek Pickard
- Cambridge Institute for Therapeutic Immunology & Infectious Disease, University of Cambridge Department of Medicine, Cambridge, United Kingdom
| | - Peter Schierack
- Institute of Biotechnology, Faculty Environment and Natural Sciences, BTU Cottbus-Senftenberg, Senftenberg, Germany
- Faculty of Health Sciences, Public Health Campus, Brandenburg, Germany
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12
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Sofia MK, Dziejman M. DksA coordinates bile-mediated regulation of virulence-associated phenotypes in type three secretion system-positive Vibrio cholerae. MICROBIOLOGY-SGM 2020; 167. [PMID: 33332258 DOI: 10.1099/mic.0.001006] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
In order to cause disease, pathogenic strains of Vibrio cholerae rely on intricate regulatory networks to orchestrate the transition between their native aquatic environment and the human host. For example, bacteria in a nutrient-starved environment undergo a metabolic shift called the stringent response, which is mediated by the alarmone ppGpp and an RNA-polymerase binding transcriptional factor, DksA. In O1 serogroup strains of V. cholerae, which use the toxin co-regulated pilus (TCP) and cholera toxin (CT) as primary virulence factors, DksA was reported to have additional functions as a mediator of virulence gene expression. However, little is known about the regulatory networks coordinating virulence phenotypes in pathogenic strains that use TCP/CT-independent virulence mechanisms. We therefore investigated whether functions of DksA outside of the stringent response are conserved in type three secretion system (T3SS)-positive V. cholerae. In using the T3SS-positive clinically isolated O39 serogroup strain AM-19226, we observed an increase in dksA expression in the presence of bile at 37 °C. However, DksA was not required for wild-type levels of T3SS structural gene expression, or for colonization in vivo. Rather, data indicate that DksA positively regulates the expression of master regulators in the motility hierarchy. Interestingly, the ΔdksA strain forms a less robust biofilm than the WT parent strain at both 30 and 37 °C. We also found that DksA regulates the expression of hapR, encoding a major regulator of biofilm formation and protease expression. Athough DksA does not appear to modulate T3SS virulence factor expression, its activity is integrated into existing regulatory networks governing virulence-related phenotypes. Strain variations therefore may take advantage of conserved ancestral proteins to expand regulons responding to in vivo signals and thus coordinate multiple phenotypes important for infection.
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Affiliation(s)
- Madeline K Sofia
- Department of Microbiology and Immunology, University of Rochester School of Medicine and Dentistry, 601 Elmwood Ave., Rochester, NY 14642, USA
| | - Michelle Dziejman
- Department of Microbiology and Immunology, University of Rochester School of Medicine and Dentistry, 601 Elmwood Ave., Rochester, NY 14642, USA
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13
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Wang M, Qazi IH, Wang L, Zhou G, Han H. Salmonella Virulence and Immune Escape. Microorganisms 2020; 8:microorganisms8030407. [PMID: 32183199 PMCID: PMC7143636 DOI: 10.3390/microorganisms8030407] [Citation(s) in RCA: 48] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2020] [Revised: 03/02/2020] [Accepted: 03/10/2020] [Indexed: 02/07/2023] Open
Abstract
Salmonella genus represents the most common foodborne pathogens causing morbidity, mortality, and burden of disease in all regions of the world. The introduction of antimicrobial agents and Salmonella-specific phages has been considered as an effective intervention strategy to reduce Salmonella contamination. However, data from the United States, European countries, and low- and middle-income countries indicate that Salmonella cases are still a commonly encountered cause of bacterial foodborne diseases globally. The control programs have not been successful and even led to the emergence of some multidrug-resistant Salmonella strains. It is known that the host immune system is able to effectively prevent microbial invasion and eliminate microorganisms. However, Salmonella has evolved mechanisms of resisting host physical barriers and inhibiting subsequent activation of immune response through their virulence factors. There has been a high interest in understanding how Salmonella interacts with the host. Therefore, in the present review, we characterize the functions of Salmonella virulence genes and particularly focus on the mechanisms of immune escape in light of evidence from the emerging mainstream literature.
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Affiliation(s)
- Mengyao Wang
- Beijing Key Laboratory for Animal Genetic Improvement, College of Animal Science and Technology, China Agricultural University, Beijing 100193, China; (M.W.); (L.W.)
- Key Laboratory of Animal Genetics and Breeding of the Ministry of Agriculture, College of Animal Science and Technology, China Agricultural University, Beijing 100193, China
| | - Izhar Hyder Qazi
- Farm Animal Genetic Resources Exploration and Innovation Key Laboratory of Sichuan Province, College of Animal Science and Technology, Sichuan Agricultural University, Chengdu 611130, China;
- Department of Veterinary Anatomy and Histology, Shaheed Benazir Bhutto University of Veterinary and Animal Sciences, Sakrand 67210, Pakistan
| | - Linli Wang
- Beijing Key Laboratory for Animal Genetic Improvement, College of Animal Science and Technology, China Agricultural University, Beijing 100193, China; (M.W.); (L.W.)
- Key Laboratory of Animal Genetics and Breeding of the Ministry of Agriculture, College of Animal Science and Technology, China Agricultural University, Beijing 100193, China
| | - Guangbin Zhou
- Farm Animal Genetic Resources Exploration and Innovation Key Laboratory of Sichuan Province, College of Animal Science and Technology, Sichuan Agricultural University, Chengdu 611130, China;
- Correspondence: (H.H.); (G.Z.)
| | - Hongbing Han
- Beijing Key Laboratory for Animal Genetic Improvement, College of Animal Science and Technology, China Agricultural University, Beijing 100193, China; (M.W.); (L.W.)
- Key Laboratory of Animal Genetics and Breeding of the Ministry of Agriculture, College of Animal Science and Technology, China Agricultural University, Beijing 100193, China
- Correspondence: (H.H.); (G.Z.)
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14
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Abstract
Pathogenic bacteria experience nutritional challenges during colonization and infection of mammalian hosts. Binding of the alarmone nucleotide guanosine tetraphosphate (ppGpp) to RNA polymerase coordinates metabolic adaptations and virulence gene transcription, increasing the fitness of diverse Gram-positive and Gram-negative bacteria as well as that of actinomycetes. Gammaproteobacteria such as Salmonella synthesize ppGpp by the combined activities of the closely related RelA and SpoT synthetases. Due to its profound inhibitory effects on growth, ppGpp must be removed; in Salmonella, this process is catalyzed by the vital hydrolytic activity of the bifunctional SpoT protein. Because SpoT hydrolase activity is essential in cells expressing a functional RelA, we have a very limited understanding of unique roles these two synthetases may assume during interactions of bacterial pathogens with their hosts. We describe here a SpoT truncation mutant that lacks ppGpp synthetase activity and all C-terminal regulatory domains but retains excellent hydrolase activity. Our studies of this mutant reveal that SpoT uniquely senses the acidification of phagosomes, inducing virulence programs that increase Salmonella fitness in an acute model of infection. Our investigations indicate that the coexistence of RelA/SpoT homologues in a bacterial cell is driven by the need to mount a stringent response to a myriad of physiological and host-specific signatures. Guanosine tetraphosphate (ppGpp) and guanosine pentaphosphate (pppGpp), together named (p)ppGpp, regulate diverse aspects of Salmonella pathogenesis, including synthesis of nutrients, resistance to inflammatory mediators, and expression of secretion systems. In Salmonella, these nucleotide alarmones are generated by the synthetase activities of RelA and SpoT proteins. In addition, the (p)ppGpp hydrolase activity of the bifunctional SpoT protein is essential to preserve cell viability. The contribution of SpoT to physiology and pathogenesis has proven elusive in organisms such as Salmonella, because the hydrolytic activity of this RelA and SpoT homologue (RSH) is vital to prevent inhibitory effects of (p)ppGpp produced by a functional RelA. Here, we describe the biochemical and functional characterization of a spoT-Δctd mutant Salmonella strain encoding a SpoT protein that lacks the C-terminal regulatory elements collectively referred to as “ctd.” Salmonella expressing the spoT-Δctd variant hydrolyzes (p)ppGpp with similar kinetics to those of wild-type bacteria, but it is defective at synthesizing (p)ppGpp in response to acidic pH. Salmonella spoT-Δctd mutants have virtually normal adaptations to nutritional, nitrosative, and oxidative stresses, but poorly induce metal cation uptake systems and Salmonella pathogenicity island 2 (SPI-2) genes in response to the acidic pH of the phagosome. Importantly, spoT-Δctd mutant Salmonella replicates poorly intracellularly and is attenuated in a murine model of acute salmonellosis. Collectively, these investigations indicate that (p)ppGpp synthesized by SpoT serves a unique function in the adaptation of Salmonella to the intracellular environment of host phagocytes that cannot be compensated by the presence of a functional RelA.
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15
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Basu P, Bhadra RK. Post-transcriptional regulation of cholera toxin production in Vibrio cholerae by the stringent response regulator DksA. MICROBIOLOGY-SGM 2018; 165:102-112. [PMID: 30444469 DOI: 10.1099/mic.0.000743] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Expression of cholera toxin (CT), the principal virulence factor of the cholera pathogen Vibrio cholerae, is positively modulated by the RNA polymerase binding unusual transcription factor DksA (DksAVc) of the stringent response pathway. Here we report that even though CT (encoded by the genes ctxAB) production is downregulated in the V. cholerae ΔdksA (ΔdksAVc) mutant, the expression of the ctxA gene as well as the genes encoding different virulence regulators, namely, AphA, TcpP and ToxT, were also upregulated. Since DksAVc positively regulates HapR, a known negative regulator of CT production, the increased expression of different virulence genes in ΔdksAVc was due most probably to downregulation of HapR. There was no secretion/transport-related defect in ΔdksAVc cells because whole cell lysates of the mutant showed a negligible amount of CT accumulation similar to WT cells. To understand further, the hapR gene was deleted in ΔdksAVc background, however, the double mutant failed to rescue the CT production defect suggesting strongly towards post-transcriptional/translational regulation by DksAVc. This hypothesis was further confirmed when the site-directed mutagenesis of each or both of the conserved aspartic acid residues at positions 68 and 71 of DksAVc, which are essential for transcription initiation during the stringent response, had no effect in the regulation of CT expression. Interestingly, progressive deletion analysis indicated that the C4-type Zn finger motif present in the C-terminus of DksAVc is essential for optimal CT production. Since this motif plays important roles in DNA/RNA binding, the present study indicates a novel complex post-transcriptional regulation of CT expression by DksAVc.
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Affiliation(s)
- Pallabi Basu
- Infectious Diseases and Immunology Division, CSIR-Indian Institute of Chemical Biology, Kolkata-700 032, India
| | - Rupak K Bhadra
- Infectious Diseases and Immunology Division, CSIR-Indian Institute of Chemical Biology, Kolkata-700 032, India
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16
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Mechanisms of Bacterial Tolerance and Persistence in the Gastrointestinal and Respiratory Environments. Clin Microbiol Rev 2018; 31:31/4/e00023-18. [PMID: 30068737 DOI: 10.1128/cmr.00023-18] [Citation(s) in RCA: 91] [Impact Index Per Article: 15.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
Pathogens that infect the gastrointestinal and respiratory tracts are subjected to intense pressure due to the environmental conditions of the surroundings. This pressure has led to the development of mechanisms of bacterial tolerance or persistence which enable microorganisms to survive in these locations. In this review, we analyze the general stress response (RpoS mediated), reactive oxygen species (ROS) tolerance, energy metabolism, drug efflux pumps, SOS response, quorum sensing (QS) bacterial communication, (p)ppGpp signaling, and toxin-antitoxin (TA) systems of pathogens, such as Escherichia coli, Salmonella spp., Vibrio spp., Helicobacter spp., Campylobacter jejuni, Enterococcus spp., Shigella spp., Yersinia spp., and Clostridium difficile, all of which inhabit the gastrointestinal tract. The following respiratory tract pathogens are also considered: Staphylococcus aureus, Pseudomonas aeruginosa, Acinetobacter baumannii, Burkholderia cenocepacia, and Mycobacterium tuberculosis Knowledge of the molecular mechanisms regulating the bacterial tolerance and persistence phenotypes is essential in the fight against multiresistant pathogens, as it will enable the identification of new targets for developing innovative anti-infective treatments.
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Tapscott T, Kim JS, Crawford MA, Fitzsimmons L, Liu L, Jones-Carson J, Vázquez-Torres A. Guanosine tetraphosphate relieves the negative regulation of Salmonella pathogenicity island-2 gene transcription exerted by the AT-rich ssrA discriminator region. Sci Rep 2018; 8:9465. [PMID: 29930310 PMCID: PMC6013443 DOI: 10.1038/s41598-018-27780-9] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2017] [Accepted: 06/01/2018] [Indexed: 01/09/2023] Open
Abstract
The repressive activity of ancestral histone-like proteins helps integrate transcription of foreign genes with discrepant AT content into existing regulatory networks. Our investigations indicate that the AT-rich discriminator region located between the −10 promoter element and the transcription start site of the regulatory gene ssrA plays a distinct role in the balanced expression of the Salmonella pathogenicity island-2 (SPI2) type III secretion system. The RNA polymerase-binding protein DksA activates the ssrAB regulon post-transcriptionally, whereas the alarmone guanosine tetraphosphate (ppGpp) relieves the negative regulation imposed by the AT-rich ssrA discriminator region. An increase in the GC-content of the ssrA discriminator region enhances ssrAB transcription and SsrB translation, thus activating the expression of downstream SPI2 genes. A Salmonella strain expressing a GC-rich ssrA discriminator region is attenuated in mice and grows poorly intracellularly. The combined actions of ppGpp and DksA on SPI2 expression enable Salmonella to grow intracellularly, and cause disease in a murine model of infection. Collectively, these findings indicate that (p)ppGpp relieves the negative regulation associated with the AT-rich discriminator region in the promoter of the horizontally-acquired ssrA gene, whereas DksA activates ssrB gene expression post-transcriptionally. The combined effects of (p)ppGpp and DksA on the ssrAB locus facilitate a balanced SPI2 virulence gene transcription that is essential for Salmonella pathogenesis.
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Affiliation(s)
- Timothy Tapscott
- Molecular Biology Program, University of Colorado School of Medicine, Aurora, CO, USA
| | - Ju-Sim Kim
- Department of Immunology and Microbiology, University of Colorado School of Medicine, Aurora, CO, USA
| | - Matthew A Crawford
- Department of Immunology and Microbiology, University of Colorado School of Medicine, Aurora, CO, USA
| | - Liam Fitzsimmons
- Department of Immunology and Microbiology, University of Colorado School of Medicine, Aurora, CO, USA
| | - Lin Liu
- Department of Immunology and Microbiology, University of Colorado School of Medicine, Aurora, CO, USA
| | - Jessica Jones-Carson
- Department of Immunology and Microbiology, University of Colorado School of Medicine, Aurora, CO, USA.,Division of Infectious Diseases, University of Colorado School of Medicine, Aurora, CO, USA
| | - Andrés Vázquez-Torres
- Molecular Biology Program, University of Colorado School of Medicine, Aurora, CO, USA. .,Department of Immunology and Microbiology, University of Colorado School of Medicine, Aurora, CO, USA. .,Veterans Affairs Eastern Colorado Health Care System, Denver, CO, USA.
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18
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Conversion of RpoS - Attenuated Salmonella enterica Serovar Typhi Vaccine Strains to RpoS + Improves Their Resistance to Host Defense Barriers. mSphere 2018; 3:mSphere00006-18. [PMID: 29507892 PMCID: PMC5830471 DOI: 10.1128/msphere.00006-18] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2018] [Accepted: 01/30/2018] [Indexed: 12/13/2022] Open
Abstract
Recombinant attenuated Salmonella vaccines (RASVs) represent a unique prevention strategy to combating infectious disease because they utilize the ability of Salmonella to invade and colonize deep effector lymphoid tissues and deliver hetero- and homologous derived antigens at the lowest immunizing dose. Our recent clinical trial in human volunteers indicated that an RpoS+ derivative of Ty2 was better at inducing immune responses than its RpoS− counterpart. In this study, we demonstrate that a functional RpoS allele is beneficial for developing effective live attenuated vaccines against S. Typhi or in using S. Typhi as a recombinant attenuated vaccine vector to deliver other protective antigens. The vast majority of live attenuated typhoid vaccines are constructed from the Salmonella enterica serovar Typhi strain Ty2, which is devoid of a functioning alternative sigma factor, RpoS, due to the presence of a frameshift mutation. RpoS is a specialized sigma factor that plays an important role in the general stress response of a number of Gram-negative organisms, including Salmonella. Previous studies have demonstrated that this sigma factor is necessary for survival following exposure to acid, hydrogen peroxide, nutrient-limiting conditions, and starvation. In addition, studies with Salmonella enterica serovar Typhimurium and the mouse model of typhoid fever have shown that RpoS is important in colonization and survival within the infected murine host. We converted 4 clinically studied candidate typhoid vaccine strains derived from Ty2 [CVD908-htrA, Ty800, and χ9639(pYA3493)] and the licensed live typhoid vaccine Ty21a (also derived from Ty2) to RpoS+ and compared their abilities to withstand environmental stresses that may be encountered within the host to those of the RpoS− parent strains. The results of our study indicate that strains that contain a functional RpoS were better able to survive following stress and that they would be ideal for further development as safe, effective vaccines to prevent S. Typhi infections or as vectors in recombinant attenuated Salmonella vaccines (RASVs) designed to protect against other infectious disease agents in humans. The S. Typhi strains constructed and described here will be made freely available upon request, as will the suicide vector used to convert rpoS mutants to RpoS+. IMPORTANCE Recombinant attenuated Salmonella vaccines (RASVs) represent a unique prevention strategy to combating infectious disease because they utilize the ability of Salmonella to invade and colonize deep effector lymphoid tissues and deliver hetero- and homologous derived antigens at the lowest immunizing dose. Our recent clinical trial in human volunteers indicated that an RpoS+ derivative of Ty2 was better at inducing immune responses than its RpoS− counterpart. In this study, we demonstrate that a functional RpoS allele is beneficial for developing effective live attenuated vaccines against S. Typhi or in using S. Typhi as a recombinant attenuated vaccine vector to deliver other protective antigens.
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19
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Endogenously generated 2-aminoacrylate inhibits motility in Salmonella enterica. Sci Rep 2017; 7:12971. [PMID: 29021529 PMCID: PMC5636819 DOI: 10.1038/s41598-017-13030-x] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2017] [Accepted: 09/19/2017] [Indexed: 11/21/2022] Open
Abstract
Members of the broadly distributed Rid/YER057c/UK114 protein family have imine/enamine deaminase activity, notably on 2-aminoacrylate (2AA). Strains of Salmonella enterica, and other organisms lacking RidA, have diverse growth phenotypes, attributed to the accumulation of 2AA. In S. enterica, 2AA inactivates a number of pyridoxal 5’-phosephate(PLP)-dependent enzymes, some of which have been linked to the growth phenotypes of a ridA mutant. This study used transcriptional differences between S. enterica wild-type and ridA strains to explore the breadth of the cellular consequences that resulted from accumulation of 2AA. Accumulation of endogenously generated 2AA in a ridA mutant resulted in lower expression of genes encoding many flagellar assembly components, which led to a motility defect. qRT-PCR results were consistent with the motility phenotype of a ridA mutant resulting from a defect in FlhD4C2 activity. In total, the results of comparative transcriptomics correctly predicted a 2AA-dependent motility defect and identified additional areas of metabolism impacted by the metabolic stress of 2AA in Salmonella enterica. Further, the data emphasized the value of integrating global approaches with biochemical genetic approaches to understand the complex system of microbial metabolism.
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20
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Marzel A, Desai PT, Goren A, Schorr YI, Nissan I, Porwollik S, Valinsky L, McClelland M, Rahav G, Gal-Mor O. Persistent Infections by Nontyphoidal Salmonella in Humans: Epidemiology and Genetics. Clin Infect Dis 2016; 62:879-886. [PMID: 26740515 DOI: 10.1093/cid/civ1221] [Citation(s) in RCA: 74] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2015] [Accepted: 12/22/2015] [Indexed: 11/13/2022] Open
Abstract
BACKGROUND Although chronic infections by typhoidal Salmonella are well-known, prolonged human infections by nontyphoidal Salmonella (NTS) are poorly characterized. METHODS We retrospectively analyzed 48 345 culture-confirmed NTS infections that occurred in Israel 1995-2012. A case-control study was performed to identify risk factors associated with persistent infections. Whole-genome-sequencing, pulsed-field gel electrophoresis (PFGE), and a mouse infection model were used to study genetic and phenotypic differences between same-patient persistent, recurring isolates. RESULTS In total, 1047 cases of persistent NTS infections, comprising 2.2% of all reported cases of salmonellosis, were identified. The persistence periods ranged between 30 days to 8.3 years. The majority (93%) of the persistently infected patients were immunocompetent, and 65% were symptomatic with relapsing diarrhea, indicating a distinct clinical manifestation from the asymptomatic carriage of typhoidal Salmonella. Four NTS serovars (Mbandaka, Bredeney, Infantis and Virchow) were found to be significantly more frequently associated with persistence than others. Comparative genomics between early and later isolates obtained from the same patients confirmed clonal infection and showed 0 to 10 SNPs between persistent isolates. A different composition of mobile genetic elements (plasmids and phages) or amino acid substitutions in global regulators was identified in multiple cases. These changes resulted in differences in phenotype and virulence between early and later same-patient isolates. CONCLUSIONS These results illuminate the overlooked clinical manifestation of persistent salmonellosis that can serve as a human reservoir for NTS infections. Additionally, we demonstrate mechanisms of in-host microevolution and exhibit their potential to shape Salmonella pathogenicity, antimicrobial resistance and host-pathogen interactions.
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Affiliation(s)
- Alex Marzel
- Infectious Diseases Research Laboratory, Sheba Medical Center, Tel-Hashomer.,Department of Epidemiology and Preventive Medicine, Sackler Faculty of Medicine, Tel Aviv University, Israel
| | - Prerak T Desai
- Department of Microbiology and Molecular Genetics, University of California, Irvine
| | - Alina Goren
- Infectious Diseases Research Laboratory, Sheba Medical Center, Tel-Hashomer.,Department of Clinical Microbiology and Immunology, Sackler Faculty of Medicine, Tel Aviv University
| | | | | | - Steffen Porwollik
- Department of Microbiology and Molecular Genetics, University of California, Irvine
| | - Lea Valinsky
- Ministry of Health Central Laboratories, Jerusalem
| | - Michael McClelland
- Department of Microbiology and Molecular Genetics, University of California, Irvine
| | - Galia Rahav
- Infectious Diseases Research Laboratory, Sheba Medical Center, Tel-Hashomer.,Sackler Faculty of Medicine, Tel Aviv University, Israel
| | - Ohad Gal-Mor
- Infectious Diseases Research Laboratory, Sheba Medical Center, Tel-Hashomer.,Department of Clinical Microbiology and Immunology, Sackler Faculty of Medicine, Tel Aviv University
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21
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The Stringent Response Regulator DksA Is Required for Salmonella enterica Serovar Typhimurium Growth in Minimal Medium, Motility, Biofilm Formation, and Intestinal Colonization. Infect Immun 2015; 84:375-84. [PMID: 26553464 DOI: 10.1128/iai.01135-15] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2015] [Accepted: 11/03/2015] [Indexed: 02/04/2023] Open
Abstract
Salmonella enterica serovar Typhimurium is a facultative intracellular human and animal bacterial pathogen posing a major threat to public health worldwide. Salmonella pathogenicity requires complex coordination of multiple physiological and virulence pathways. DksA is a conserved Gram-negative regulator that belongs to a distinct group of transcription factors that bind directly to the RNA polymerase secondary channel, potentiating the effect of the signaling molecule ppGpp during a stringent response. Here, we established that in S. Typhimurium, dksA is induced during the logarithmic phase and DksA is essential for growth in minimal defined medium and plays an important role in motility and biofilm formation. Furthermore, we determined that DksA positively regulates the Salmonella pathogenicity island 1 and motility-chemotaxis genes and is necessary for S. Typhimurium invasion of human epithelial cells and uptake by macrophages. In contrast, DksA was found to be dispensable for S. Typhimurium host cell adhesion. Finally, using the colitis mouse model, we found that dksA is spatially induced at the midcecum during the early stage of the infection and required for gastrointestinal colonization and systemic infection in vivo. Taken together, these data indicate that the ancestral stringent response regulator DksA coordinates various physiological and virulence S. Typhimurium programs and therefore is a key virulence regulator of Salmonella.
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