scholarly journals Identification and Characterization of Putative Translocated Effector Proteins of the Edwardsiella ictaluri Type III Secretion System

mSphere ◽  
2016 ◽  
Vol 1 (3) ◽  
Author(s):  
Lidiya P. Dubytska ◽  
Matthew L. Rogge ◽  
Ronald L. Thune
Keyword(s):  
Host Cell ◽  
Channel Catfish ◽  
Bacterial Pathogen ◽  
The United States ◽  
Secretion System ◽  
Edwardsiella Ictaluri ◽  
Cell Physiology ◽  
Intracellular Replication ◽  
Content Type ◽  
Significant Disease

ABSTRACT The bacterial pathogen Edwardsiella ictaluri causes enteric septicemia of catfish (ESC), an economically significant disease of farm-raised channel catfish. Commercial catfish production accounts for the majority of the total fin fish aquaculture in the United States, with almost 300,000 tons produced annually, and ESC is the leading cause of disease loss in the industry. We have demonstrated the survival and replication of E. ictaluri within channel catfish cells and identified a secretion system that is essential for E. ictaluri intracellular replication and virulence. We have also identified nine proteins encoded in the E. ictaluri genome that we believe are actively transferred from the bacterium to the cytoplasm of the host cell and act to manipulate host cell physiology to the advantage of the bacterium. The data presented here confirm that the proteins are actually transferred during an infection, which will lead to further work on approaches to preventing or controlling ESC. Edwardsiella ictaluri, a major pathogen in channel catfish aquaculture, encodes a type III secretion system (T3SS) that is essential for intracellular replication and virulence. Previous work identified three putative T3SS effectors in E. ictaluri, and in silico analysis of the E. ictaluri genome identified six additional putative effectors, all located on the chromosome outside the T3SS pathogenicity island. To establish active translocation by the T3SS, we constructed translational fusions of each effector to the amino-terminal adenylate cyclase (AC) domain of the Bordetella pertussis adenylate cyclase toxin CyaA. When translocated through the membrane of the Edwardsiella-containing vacuole (ECV), the cyclic AMP produced by the AC domain in the presence of calmodulin in the host cell cytoplasm can be measured. Results showed that all nine effectors were translocated from E. ictaluri in the ECV to the cytoplasm of the host cells in the wild-type strain but not in a T3SS mutant, indicating that translocation is dependent on the T3SS machinery. This confirms that the E. ictaluri T3SS is similar to the Salmonella pathogenicity island 2 T3SS in that it translocates effectors through the membrane of the bacterial vacuole directly into the host cell cytoplasm. Additional work demonstrated that both initial acidification and subsequent neutralization of the ECV were necessary for effector translocation, except for two of them that did not require neutralization. Single-gene mutants constructed for seven of the individual effectors were all attenuated for replication in CCO cells, but only three were replication deficient in head kidney-derived macrophages (HKDM). IMPORTANCE The bacterial pathogen Edwardsiella ictaluri causes enteric septicemia of catfish (ESC), an economically significant disease of farm-raised channel catfish. Commercial catfish production accounts for the majority of the total fin fish aquaculture in the United States, with almost 300,000 tons produced annually, and ESC is the leading cause of disease loss in the industry. We have demonstrated the survival and replication of E. ictaluri within channel catfish cells and identified a secretion system that is essential for E. ictaluri intracellular replication and virulence. We have also identified nine proteins encoded in the E. ictaluri genome that we believe are actively transferred from the bacterium to the cytoplasm of the host cell and act to manipulate host cell physiology to the advantage of the bacterium. The data presented here confirm that the proteins are actually transferred during an infection, which will lead to further work on approaches to preventing or controlling ESC.

scholarly journals Regulation of the Edwardsiella ictaluri Type III Secretion System by pH and Phosphate Concentration through EsrA, EsrB, and EsrC

2011 ◽  
Vol 77 (13) ◽  
pp. 4293-4302 ◽  
Author(s):  
Matthew L. Rogge ◽  
Ronald L. Thune
Keyword(s):  
Channel Catfish ◽  
Type Iii Secretion ◽  
Type Iii Secretion System ◽  
Pathogenicity Island ◽  
Low Ph ◽  
Secretion System ◽  
Edwardsiella Ictaluri ◽  
Phosphate Limitation ◽  
Content Type ◽  
Type Iii

ABSTRACTA recently describedEdwardsiella ictaluritype III secretion system (T3SS) with functional similarity to theSalmonellapathogenicity island 2 T3SS is required for replication in channel catfish head-kidney-derived macrophages (HKDM) and virulence in channel catfish. Quantitative PCR and Western blotting identified low pH and phosphate limitation as conducive to expression of theE. ictaluriT3SS, growth conditions that mimic the phagosomal environment. Mutagenesis studies demonstrated that expression is under the control of the EsrAB two-component regulatory system. EsrB also induces upregulation of the AraC-type regulatory protein EsrC, which enhances expression of the EscB/EseG chaperone/effector operon in concert with EsrB and induces expression of the pEI1-encoded effector, EseH. EsrC also induces expression of a putative type VI secretion system translocon protein, EvpC, which is secreted under the same low-pH conditions as the T3SS translocon proteins. The pEI2-encoded effector, EseI, was upregulated under low-pH and low-phosphate conditions but not in an EsrB- or EsrC-dependent manner. Mutations of EsrA and EsrB both resulted in loss of the ability to replicate in HKDM and full attenuation in the channel catfish host. Mutation of EsrC did not affect intracellular replication but did result in attenuation in catfish. Although EsrB is the primary transcriptional regulator forE. ictalurigenes within the T3SS pathogenicity island, EsrC regulates expression of the plasmid-carried effectoreseHand appears to mediate coordinated expression of the T6SS with the T3SS.

scholarly journals Protein Kinase LegK2 Is a Type IV Secretion System Effector Involved in Endoplasmic Reticulum Recruitment and Intracellular Replication of Legionella pneumophila

2011 ◽  
Vol 79 (5) ◽  
pp. 1936-1950 ◽  
Author(s):  
Eva Hervet ◽  
Xavier Charpentier ◽  
Anne Vianney ◽  
Jean-Claude Lazzaroni ◽  
Christophe Gilbert ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Protein Kinase ◽  
Host Cell ◽  
Legionella Pneumophila ◽  
Secretion System ◽  
Type Iv Secretion ◽  
Type Iv Secretion System ◽  
Intracellular Replication ◽  
Content Type ◽  
Type Iv

ABSTRACTLegionella pneumophilais the etiological agent of Legionnaires' disease. Crucial to the pathogenesis of this intracellular pathogen is its ability to subvert host cell defenses, permitting intracellular replication in specialized vacuoles within host cells. The Dot/Icm type IV secretion system (T4SS), which translocates a large number of bacterial effectors into host cell, is absolutely required for rerouting theLegionellaphagosome. ManyLegionellaeffectors display distinctive eukaryotic domains, among which are protein kinase domains.In silicoanalysis andin vitrophosphorylation assays identified five functional protein kinases, LegK1 to LegK5, encoded by the epidemicL. pneumophilaLens strain. Except for LegK5, theLegionellaprotein kinases are all T4SS effectors. LegK2 plays a key role in bacterial virulence, as demonstrated by gene inactivation. ThelegK2mutant containing vacuoles displays less-efficient recruitment of endoplasmic reticulum markers, which results in delayed intracellular replication. Considering that a kinase-dead substitution mutant oflegK2exhibits the same virulence defects, we highlight here a new molecular mechanism, namely, protein phosphorylation, developed byL. pneumophilato establish a replicative niche and evade host cell defenses.

scholarly journals Biogenesis of the Spacious Coxiella-Containing Vacuole Depends on Host Transcription Factors TFEB and TFE3

2019 ◽  
Vol 88 (3) ◽  
Author(s):  
Bhavna Padmanabhan ◽  
Laura F. Fielden ◽  
Abderrahman Hachani ◽  
Patrice Newton ◽  
David R. Thomas ◽  
...  
Keyword(s):  
Transcription Factors ◽  
Host Cell ◽  
Isotope Labeling ◽  
Nuclear Translocation ◽  
Bacterial Pathogen ◽  
Effector Proteins ◽  
Content Type ◽  
Cellular Processes ◽  
Type Iv ◽  
Lysosome Biogenesis

ABSTRACT Coxiella burnetii is an obligate intracellular bacterial pathogen that replicates inside the lysosome-derived Coxiella-containing vacuole (CCV). To establish this unique niche, C. burnetii requires the Dot/Icm type IV secretion system (T4SS) to translocate a cohort of effector proteins into the host cell, which modulate multiple cellular processes. To characterize the host-pathogen interactions that occur during C. burnetii infection, stable-isotope labeling by amino acids in cell culture (SILAC)-based proteomics was used to identify changes in the host proteome during infection of a human-derived macrophage cell line. These data revealed that the abundances of many proteins involved in host cell autophagy and lysosome biogenesis were increased in infected cells. Thus, the role of the host transcription factors TFEB and TFE3, which regulate the expression of a network of genes involved in autophagy and lysosomal biogenesis, were examined in the context of C. burnetii infection. During infection with C. burnetii, both TFEB and TFE3 were activated, as demonstrated by the transport of these proteins from the cytoplasm into the nucleus. The nuclear translocation of these transcription factors was shown to be dependent on the T4SS, as a Dot/Icm mutant showed reduced nuclear translocation of TFEB and TFE3. This was supported by the observation that blocking bacterial translation with chloramphenicol resulted in the movement of TFEB and TFE3 back into the cytoplasm. Silencing of the TFEB and TFE3 genes, alone or in combination, significantly reduced the size of the CCV, which indicates that these host transcription factors facilitate the expansion and maintenance of the organelle that supports C. burnetii intracellular replication.

scholarly journals Impact of Active Metabolism onChlamydia trachomatisElementary Body Transcript Profile and Infectivity

2018 ◽  
Vol 200 (14) ◽  
Author(s):  
Scott Grieshaber ◽  
Nicole Grieshaber ◽  
Hong Yang ◽  
Briana Baxter ◽  
Ted Hackstadt ◽  
...  
Keyword(s):  
United States ◽  
Host Cell ◽  
Terminal Differentiation ◽  
The United States ◽  
Target Cells ◽  
Developmental Cycle ◽  
Content Type ◽  
Obligate Intracellular ◽  
Cell Form ◽  
Mucosal Surfaces

ABSTRACTBacteria of the genusChlamydiainclude the significant human pathogensChlamydia trachomatisandC. pneumoniae. All chlamydiae are obligate intracellular parasites that depend on infection of a host cell and transition through a biphasic developmental cycle. Following host cell invasion by the infectious elementary body (EB), the pathogen transitions to the replicative but noninfectious reticulate body (RB). Differentiation of the RB back to the EB is essential to generate infectious progeny. While the EB form has historically been regarded as metabolically inert, maintenance of infectivity during incubation with specific nutrients has revealed active maintenance of the infectious phenotype. Using transcriptome sequencing, we show that the transcriptome of extracellular EBs incubated under metabolically stimulating conditions does not cluster with germinating EBs but rather with the transcriptome of EBs isolated directly from infected cells. In addition, the transcriptional profile of the extracellular metabolizing EBs more closely resembled that of EB production than germination. Maintenance of infectivity of extracellular EBs was achieved by metabolizing chemically diverse compounds, including glucose 6-phosphate, ATP, and amino acids, all of which can be found in extracellular environments, including mucosal secretions. We further show that the EB cell type actively maintains infectivity in the inclusion after terminal differentiation. Overall, these findings contribute to the emerging understanding that the EB cell form is actively maintained through metabolic processes after terminal differentiation to facilitate prolonged infectivity within the inclusion and under host cell free conditions, for example, following deposition at mucosal surfaces.IMPORTANCEChlamydiae are obligate intracellular Gram-negative bacteria that are responsible for a wide range of diseases in both animal and human hosts. According to the Centers for Disease Control and Prevention,C. trachomatisis the most frequently reported sexually transmitted infection in the United States, costing the American health care system nearly $2.4 billion annually. Every year, there are over 4 million new cases ofChlamydiainfections in the United States and an estimated 100 million cases worldwide. To cause disease,Chlamydiamust successfully complete its complex biphasic developmental cycle, alternating between an infectious cell form (EB) specialized for initiating entry into target cells and a replicative form (RB) specialized for creating and maintaining the intracellular replication niche. The EB cell form has historically been considered metabolically quiescent, a passive entity simply waiting for contact with a host cell to initiate the next round of infection. Recent studies and data presented here demonstrate that the EB maintains its infectious phenotype by actively metabolizing a variety of nutrients. Therefore, the EB appears to have an active role in chlamydial biology, possibly within multiple environments, such as mucosal surfaces, fomites, and inside the host cell after formation.

scholarly journals Novel Type III Effectors in Pseudomonas aeruginosa

mBio ◽  
2015 ◽  
Vol 6 (2) ◽  
Author(s):  
David Burstein ◽  
Shirley Satanower ◽  
Michal Simovitch ◽  
Yana Belnik ◽  
Meital Zehavi ◽  
...  
Keyword(s):  
Machine Learning ◽  
Pseudomonas Aeruginosa ◽  
Host Cell ◽  
Type Iii Secretion ◽  
Type Iii Secretion System ◽  
Secretion System ◽  
Content Type ◽  
Machine Learning Classification ◽  
Type Iii ◽  
Wide Range

ABSTRACT Pseudomonas aeruginosa is a Gram-negative, opportunistic pathogen that causes chronic and acute infections in immunocompromised patients. Most P. aeruginosa strains encode an active type III secretion system (T3SS), utilized by the bacteria to deliver effector proteins from the bacterial cell directly into the cytoplasm of the host cell. Four T3SS effectors have been discovered and extensively studied in P. aeruginosa: ExoT, ExoS, ExoU, and ExoY. This is especially intriguing in light of P. aeruginosa's ability to infect a wide range of hosts. We therefore hypothesized that additional T3SS effectors that have not yet been discovered are encoded in the genome of P. aeruginosa. Here, we applied a machine learning classification algorithm to identify novel P. aeruginosa effectors. In this approach, various types of data are integrated to differentiate effectors from the rest of the open reading frames of the bacterial genome. Due to the lack of a sufficient learning set of positive effectors, our machine learning algorithm integrated genomic information from another Pseudomonas species and utilized dozens of features accounting for various aspects of the effector coding genes and their products. Twelve top-ranking predictions were experimentally tested for T3SS-specific translocation, leading to the discovery of two novel T3SS effectors. We demonstrate that these effectors are not part of the injection structural complex and report initial efforts toward their characterization. IMPORTANCE Pseudomonas aeruginosa uses a type III secretion system (T3SS) to secrete toxic proteins, termed effectors, directly into the cytoplasm of the host cell. The activation of this secretion system is correlated with disease severity and patient death. Compared with many other T3SS-utilizing pathogenic bacteria, P. aeruginosa has a fairly limited arsenal of effectors that have been identified. This is in sharp contrast with the wide range of hosts that this bacterium can infect. The discovery of two novel effectors described here is an important step toward better understanding of the virulence and host evasion mechanisms adopted by this versatile pathogen and may provide novel approaches to treat P. aeruginosa infections.

scholarly journals Coxiella burnetii Effector Proteins That Localize to the Parasitophorous Vacuole Membrane Promote Intracellular Replication

2014 ◽  
Vol 83 (2) ◽  
pp. 661-670 ◽  
Author(s):  
Charles L. Larson ◽  
Paul A. Beare ◽  
Daniel E. Voth ◽  
Dale Howe ◽  
Diane C. Cockrell ◽  
...  
Keyword(s):  
Coxiella Burnetii ◽  
Parasitophorous Vacuole ◽  
Coiled Coil ◽  
Bacterial Pathogen ◽  
Effector Proteins ◽  
Intracellular Replication ◽  
Intracellular Growth ◽  
Content Type ◽  
Cell Cytosol ◽  
Pv Generation

The intracellular bacterial pathogenCoxiella burnetiidirects biogenesis of a parasitophorous vacuole (PV) that acquires host endolysosomal components. Formation of a PV that supportsC. burnetiireplication requires a Dot/Icm type 4B secretion system (T4BSS) that delivers bacterial effector proteins into the host cell cytosol. Thus, a subset of T4BSS effectors are presumed to direct PV biogenesis. Recently, the PV-localized effector protein CvpA was found to promoteC. burnetiiintracellular growth and PV expansion. We predict additionalC. burnetiieffectors localize to the PV membrane and regulate eukaryotic vesicle trafficking events that promote pathogen growth. To identify these vacuolar effector proteins, a list of predictedC. burnetiiT4BSS substrates was compiled using bioinformatic criteria, such as the presence of eukaryote-like coiled-coil domains. Adenylate cyclase translocation assays revealed 13 proteins were secreted in a Dot/Icm-dependent fashion byC. burnetiiduring infection of human THP-1 macrophages. Four of the Dot/Icm substrates, termedCoxiellavacuolarprotein B (CvpB), CvpC, CvpD, and CvpE, labeled the PV membrane and LAMP1-positive vesicles when ectopically expressed as fluorescently tagged fusion proteins.C. burnetiiΔcvpB, ΔcvpC, ΔcvpD, and ΔcvpEmutants exhibited significant defects in intracellular replication and PV formation. Genetic complementation of the ΔcvpDand ΔcvpEmutants rescued intracellular growth and PV generation, whereas the growth ofC. burnetiiΔcvpBand ΔcvpCwas rescued upon cohabitation with wild-type bacteria in a common PV. Collectively, these data indicateC. burnetiiencodes multiple effector proteins that target the PV membrane and benefit pathogen replication in human macrophages.

scholarly journals The Legionella Kinase LegK2 Targets the ARP2/3 Complex To Inhibit Actin Nucleation on Phagosomes and Allow Bacterial Evasion of the Late Endocytic Pathway

mBio ◽  
2015 ◽  
Vol 6 (3) ◽  
Author(s):  
Céline Michard ◽  
Daniel Sperandio ◽  
Nathalie Baïlo ◽  
Javier Pizarro-Cerdá ◽  
Lawrence LeClaire ◽  
...  
Keyword(s):  
Protein Kinase ◽  
Host Cell ◽  
Legionella Pneumophila ◽  
Actin Polymerization ◽  
Secretion System ◽  
Endocytic Pathway ◽  
Specific Chemical ◽  
Actin Remodeling ◽  
Content Type

ABSTRACTLegionella pneumophila, the etiological agent of legionellosis, replicates within phagocytic cells. Crucial to biogenesis of the replicative vacuole is the Dot/Icm type 4 secretion system, which translocates a large number of effectors into the host cell cytosol. Among them is LegK2, a protein kinase that plays a key role inLegionellainfection. Here, we identified the actin nucleator ARP2/3 complex as a target of LegK2. LegK2 phosphorylates the ARPC1B and ARP3 subunits of the ARP2/3 complex. LegK2-dependent ARP2/3 phosphorylation triggers global actin cytoskeleton remodeling in cells, and it impairs actin tail formation byListeria monocytogenes, a well-known ARP2/3-dependent process. During infection, LegK2 is addressed to theLegionella-containing vacuole surface and inhibits actin polymerization on the phagosome, as revealed by legK2 gene inactivation. Consequently, LegK2 prevents late endosome/lysosome association with the phagosome and finally contributes to remodeling of the bacterium-containing phagosome into a replicative niche. The inhibition of actin polymerization by LegK2 and its effect on endosome trafficking are ARP2/3 dependent since it can be phenocopied by a specific chemical inhibitor of the ARP2/3 complex. Thus, LegK2-ARP2/3 interplay highlights an original mechanism of bacterial virulence with an unexpected role in local actin remodeling that allows bacteria to control vesicle trafficking in order to escape host defenses.IMPORTANCEDeciphering the individual contribution of each Dot/Icm type 4 secretion system substrate to the intracellular life-style ofL. pneumophilaremains the principal challenge in understanding the molecular basis ofLegionellavirulence. Our finding that LegK2 is a Dot/Icm effector that inhibits actin polymerization on theLegionella-containing vacuole importantly contributes to the deciphering of the molecular mechanisms evolved byLegionellato counteract the endocytic pathway. Indeed, our results highlight the essential role of LegK2 in preventing late endosomes from fusing with the phagosome. More generally, this work is the first demonstration of local actin remodeling as a mechanism used by bacteria to control organelle trafficking. Further, by characterizing the role of the bacterial protein kinase LegK2, we reinforce the concept that posttranslational modifications are key strategies used by pathogens to evade host cell defenses.

scholarly journals Dependency of Coxiella burnetii Type 4B Secretion on the Chaperone IcmS

2019 ◽  
Vol 201 (23) ◽  
Author(s):  
Charles L. Larson ◽  
Paul A. Beare ◽  
Robert A. Heinzen
Keyword(s):  
Host Cell ◽  
Coxiella Burnetii ◽  
Legionella Pneumophila ◽  
Q Fever ◽  
Secretion System ◽  
Host Cells ◽  
Growth Defect ◽  
Wild Type ◽  
Signal Sequences ◽  
Content Type

ABSTRACT Macrophage parasitism by Coxiella burnetii, the cause of human Q fever, requires the translocation of proteins with effector functions directly into the host cell cytosol via a Dot/Icm type 4B secretion system (T4BSS). Secretion by the analogous Legionella pneumophila T4BSS involves signal sequences within the C-terminal and internal domains of effector proteins. The cytoplasmic chaperone pair IcmSW promotes secretion and binds internal sites distinct from signal sequences. In the present study, we investigated requirements of C. burnetii IcmS for host cell parasitism and effector translocation. A C. burnetii icmS deletion mutant (ΔicmS) exhibited impaired replication in Vero epithelial cells, deficient formation of the Coxiella-containing vacuole, and aberrant T4BSS secretion. Three secretion phenotypes were identified from a screen of 50 Dot/Icm substrates: IcmS dependent (secreted by only wild-type bacteria), IcmS independent (secreted by both wild-type and ΔicmS bacteria), or IcmS inhibited (secreted by only ΔicmS bacteria). Secretion was assessed for N-terminal or C-terminal truncated forms of CBU0794 and CBU1525. IcmS-inhibited secretion of CBU1525 required a C-terminal secretion signal whereas IcmS-dependent secretion of CBU0794 was directed by C-terminal and internal signals. Interchange of the C-terminal 50 amino acids of CBU0794 and CBU1525 revealed that sites within the C terminus regulate IcmS dependency. Glutathione S-transferase-tagged IcmSW bound internal sequences of IcmS-dependent and -inhibited substrates. Thus, the growth defect of the C. burnetii ΔicmS strain is associated with a loss of T4BSS chaperone activity that both positively and negatively regulates effector translocation. IMPORTANCE The intracellular pathogen Coxiella burnetii employs a type 4B secretion system (T4BSS) that promotes growth by translocating effectors of eukaryotic pathways into host cells. T4BSS regulation modeled in Legionella pneumophila indicates IcmS facilitates effector translocation. Here, we characterized type 4B secretion by a Coxiella ΔicmS mutant that exhibits intracellular growth defects. T4BSS substrates demonstrated increased, equivalent, or decreased secretion by the ΔicmS mutant relative to wild-type Coxiella. Similar to the Legionella T4BSS, IcmS dependency in Coxiella was determined by C-terminal and/or internal secretion signals. However, IcmS inhibited secretion of some effectors by Coxiella that were previously shown to be translocated by Legionella. Thus, Coxiella has a unique IcmS regulatory mechanism that both positively and negatively regulates T4BSS export.

scholarly journals Noncanonical Inhibition of mTORC1 byCoxiella burnetiiPromotes Replication within a Phagolysosome-Like Vacuole

mBio ◽  
2019 ◽  
Vol 10 (1) ◽  
Author(s):  
Charles L. Larson ◽  
Kelsi M. Sandoz ◽  
Diane C. Cockrell ◽  
Robert A. Heinzen
Keyword(s):  
Host Cell ◽  
Coxiella Burnetii ◽  
Secretion System ◽  
Effector Proteins ◽  
Nutrient Deprivation ◽  
Autophagic Flux ◽  
Content Type ◽  
Mechanistic Target Of Rapamycin ◽  
Infected Cells ◽  
Bacterial Replication

ABSTRACTThe Q fever agentCoxiella burnetiiis a Gram-negative bacterium that invades macrophages and replicates inside a specialized lysosomal vacuole. The pathogen employs a type 4B secretion system (T4BSS) to deliver effector proteins into the host cell that modify theCoxiella-containing vacuole (CCV) into a replication-permissive niche. Mature CCVs are massive degradative organelles that acquire lysosomal proteins. Inhibition of mammalian (or mechanistic) target of rapamycin complex 1 (mTORC1) kinase by nutrient deprivation promotes autophagy and lysosome fusion, as well as activation of the transcription factors TFE3 and TFEB (TFE3/B), which upregulates expression of lysosomal genes. Here, we report thatC. burnetiiinhibits mTORC1 as evidenced by impaired localization of mTORC1 to endolysosomal membranes and decreased phosphorylation of elF4E-binding protein 1 (4E-BP1) and S6 kinase 1 in infected cells. Infected cells exhibit increased amounts of autophagy-related proteins protein 1A/1B-light chain 3 (LC3) and p62 as well as of activated TFE3. However,C. burnetiidid not accelerate autophagy or block autophagic flux triggered by cell starvation. Activation of autophagy or transcription by TFE3/B increased CCV expansion without enhancing bacterial replication. By contrast, knockdown of tuberous sclerosis complex 1 (TSC1) or TSC2, which hyperactivates mTORC1, impaired CCV expansion and bacterial replication. Together, these data demonstrate that specific inhibition of mTORC1 byC. burnetii, but not amplified cell catabolism via autophagy, is required for optimal pathogen replication. These data reveal a complex interplay between lysosomal function and host cell metabolism that regulatesC. burnetiiintracellular growth.IMPORTANCECoxiella burnetiiis an intracellular pathogenic bacterium that replicates within a lysosomal vacuole. Biogenesis of theCoxiella-containing vacuole (CCV) requires effector proteins delivered into the host cell cytosol by the type 4B secretion system (T4BSS). Modifications to lysosomal physiology required for pathogen replication within the CCV are poorly understood. Mammalian (or mechanistic) target of rapamycin complex 1 (mTORC1) is a master kinase that regulates lysosome structure and function. Nutrient deprivation inhibits mTORC1, which promotes cell catabolism in the form of accelerated autophagy and increased lysosome biosynthesis. Here, we report thatC. burnetiigrowth is enhanced by T4BSS-dependent inhibition of mTORC1 that does not activate autophagy. Canonical inhibition of mTORC1 by starvation or inhibitor treatment that induces autophagic flux does not benefitC. burnetiigrowth. Furthermore, hyperactivation of mTORC1 impairs bacterial replication. These findings indicate thatC. burnetiiinhibition of mTORC1 without accelerated autophagy promotes bacterial growth.

scholarly journals Barcoded Consortium Infections Resolve Cell Type-Dependent Salmonella enterica Serovar Typhimurium Entry Mechanisms

mBio ◽  
2019 ◽  
Vol 10 (3) ◽  
Author(s):  
Maria Letizia Di Martino ◽  
Viktor Ek ◽  
Wolf-Dietrich Hardt ◽  
Jens Eriksson ◽  
Mikael E. Sellin
Keyword(s):  
Host Cell ◽  
Salmonella Enterica ◽  
Cell Types ◽  
Secretion System ◽  
Host Cells ◽  
Host Cell Invasion ◽  
Cell Type ◽  
Content Type ◽  
Invasion Mechanisms ◽  
Serovar Typhimurium

ABSTRACT Bacterial host cell invasion mechanisms depend on the bacterium’s virulence factors and the properties of the target cell. The enteropathogen Salmonella enterica serovar Typhimurium (S.Tm) invades epithelial cell types in the gut mucosa and a variety of immune cell types at later infection stages. The molecular mechanism(s) of host cell entry has, however, been studied predominantly in epithelial cell lines. S.Tm uses a type three secretion system (TTSS-1) to translocate effectors into the host cell cytosol, thereby sparking actin ruffle-dependent entry. The ruffles also fuel cooperative invasion by bystander bacteria. In addition, several TTSS-1-independent entry mechanisms exist, involving alternative S.Tm virulence factors, or the passive uptake of bacteria by phagocytosis. However, it remains ill-defined how S.Tm invasion mechanisms vary between host cells. Here, we developed an internally controlled and scalable method to map S.Tm invasion mechanisms across host cell types and conditions. The method relies on host cell infections with consortia of chromosomally tagged wild-type and mutant S.Tm strains, where the abundance of each strain can be quantified by qPCR or amplicon sequencing. Using this methodology, we quantified cooccurring TTSS-1-dependent, cooperative, and TTSS-1-independent invasion events in epithelial, monocyte, and macrophage cells. We found S.Tm invasion of epithelial cells and monocytes to proceed by a similar MOI-dependent mix of TTSS-1-dependent and cooperative mechanisms. TTSS-1-independent entry was more frequent in macrophages. Still, TTSS-1-dependent invasion dominated during the first minutes of interaction also with this cell type. Finally, the combined action of the SopB/SopE/SopE2 effectors was sufficient to explain TTSS-1-dependent invasion across both epithelial and phagocytic cells. IMPORTANCE Salmonella enterica serovar Typhimurium (S.Tm) is a widespread and broad-host-spectrum enteropathogen with the capacity to invade diverse cell types. Still, the molecular basis for the host cell invasion process has largely been inferred from studies of a few selected cell lines. Our work resolves the mechanisms that Salmonellae employ to invade prototypical host cell types, i.e., human epithelial, monocyte, and macrophage cells, at a previously unattainable level of temporal and quantitative precision. This highlights efficient bacterium-driven entry into innate immune cells and uncovers a type III secretion system effector module that dominates active bacterial invasion of not only epithelial cells but also monocytes and macrophages. The results are derived from a generalizable method, where we combine barcoding of the bacterial chromosome with mixed consortium infections of cultured host cells. The application of this methodology across bacterial species and infection models will provide a scalable means to address host-pathogen interactions in diverse contexts.

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