Francisella tularensis is a Gram-negative, facultative intracellular coccobacillus and the etiologic agent of tularemia for a wide variety of vertebrate and invertebrate animal species. Several species and subspecies of Francisella are currently recognized. However, the majority of infections are caused by F. tularensis subspecies tularensis (type A) and subspecies holarctica (type B). Given the low infectious dose, multiple transmission routes, severity of illness, and lack of licensed vaccines, F. tularensis has long been considered a potential biological weapon and is now classified as a category A select agent by the National Institutes of Health and the Centers for Disease Control and Prevention. The investigation of the mechanisms of pathogenesis by F. tularensis type A and B strains is hindered by the difficulty and lack of methods to mutate the putative genes that encode for virulence factors. New genetic tools have been developed that have enabled mutagenesis of F. tularensis type A and type B stains. However, site-specific mutations remain difficult to execute or these methods generate random mutations. In this study a novel method was developed to create site-directed mutations in a putative capsule biosynthesis locus to knock out encapsulation of the attenuated F. tularensis live vaccine strain. Two suicide vectors for mutagenesis of F. tularensis were constructed based on the commercial PCR cloning vector pSC-A. These vectors were created by inserting into the cloning site a kanamycin resistance gene boarded upstream by 1.3 kb of N-terminal DNA and downstream by 1.3 kb of C-terminal DNA that flanks the target gene. Cryotransformation was used to introduce the vectors into F. tularensis. Open reading frame (ORF) FTT0793, which may encode for an ABC transporter involved in capsule export, was initially selected for mutagenesis in order to generate a mutant that was nonencapsulated, but could still synthesize capsule and induce a host immune response. Mutagenesis of this gene was successful. However, phenotypic assays could not confirm that the mutant was nonencapsulated compared to the parent. Therefore, adjacent ORFs FTT0798 and FTT0799, which may encode for a galactosyl transferase and mannosyl transferase, respectively, were also deleted to completely knock out capsule synthesis. The resulting mutant appeared to be nonencapsulated as determined by negative staining transmission electron microscopy. In this study, a plasmid and method for generating allelic exchange mutants is reported, which should be useful for generating additional mutants of F. tularensis for use in clarifing the roles of specific genes. This vector is currently being used to make a nonencapsulated mutant of a virulent type A strain to determine the role of capsule in virulence. / Master of Science

The pathogen Francisella tularensis subsp. tularensis has been classified as a Center for Disease Control (CDC) select agent. However, little is still known of what makes the bacteria cause dis-ease, especially the highly virulent type A1 strains. The work in this dissertation focused on type A1 strains from the Inzana laboratory, including a wildtype virulent strain TI0902, an avirulent chemical mutant strain TIGB03 with a Single Nucleotide Polymorphism in the wbtK gene, and several complemented mutants, [wbtK+]TIGB03, with dramatic differences in virulence and growth rates. One of the complemented clones (Clone12 or avp-[wbtK+]TIGB03-C12) was aviru-lent, but protected mice against challenge of a lethal dose of TI0902 and was considered as a possible vaccine strain. Whole genome sequencing was performed to identify genetic differences between the virulent, avirulent and protective strains using both Roche/454 and Illumina next-generation sequencing technologies. Additionally, RNASeq analysis was performed to identify differentially expressed genes between the different strains. This comprehensive genomic analysis revealed the critical role of transposable elements in inducing genomic instability resulting in large du-plications and deletions in the genomes of the chemical mutant and the complemented clones that in turn affect gene dosage and expression of genes known to regulate virulence. For exam-ple, whole genome sequencing of the avirulent chemical mutant TIGB03 revealed a large 75.5 kb tandem duplication flanked by transposable elements, while the genome of a virulent Clone01 (vir-[wbtK+]TIGB03-C1) lost one copy of the 75.5 kb tandem duplicated region but gained a tandem duplication of another large 80kb region that contains a virulence associated transcription factor SspA. RNAseq data showed that the dosage effect of this extra region in Clone1 suppresses expression of MglA regulated genes. Since MglA regulates genes that are known to be crucial for virulence, including the well-studied Francisella Pathogenicity Island (FPI), these results suggest that gene dosage effects arising from large duplications can trigger unknown virulence mechanisms in F. tularensis subsp. tularensis. These results are important especially when designing live vaccine strains that have repeated insertion elements in their genomes. / Ph. D.

Au Canada, Francisella tularensis, une bactérie zoonotique causant la tularémie, affecte principalement le lièvre d’Amérique, le rat musqué et le castor. Malgré les nombreuses études sur cette maladie, les connaissances sur l’écologie et les réservoirs naturels de la tularémie demeurent limitées. Une étude transversale a été réalisée afin d’estimer la prévalence d’infection par F. tularensis chez le lièvre d’Amérique, le rat musqué et le coyote dans quatre régions du Québec (Canada) et de décrire le risque d’infection d’après des caractéristiques individuelles (âge, sexe et état de chair) et environnementales. D’octobre 2012 à avril 2013, 345 lièvres d’Amérique, 411 rats musqués et 385 coyotes capturés par des trappeurs ont été échantillonnés. Les caractéristiques environnementales autour du site de capture ont été extraites de base de données géographiques. La séroprévalence (test de microagglutination) était de 2.9% chez les coyotes, 0.6% chez les lièvres et 0% chez les rats musqués. Tous les rats musqués et les lièvres étaient négatifs à une PCR en temps réel réalisée à partir d’un pool de foie, rein, rate et poumon; par contre, le type AI a été détecté dans les organes individuels des deux lièvres séropositifs. Des analyses de régression logistique exacte ont démontré que l’âge était un facteur de risque pour la séropositivité du coyote, ainsi que la proportion de forêts et la proportion de l’environnement considéré approprié pour le lièvre autour de la localisation de capture des coyotes. Les résultats de cette étude suggèrent la présence du cycle terrestre dans les régions étudiées. / In Canada, Francisella tularensis, the zoonotic bacterial agent of tularemia, affects mostly snowshoe hares, muskrats and beavers. Despite numerous studies, knowledge of its ecological occurrence and natural reservoirs is limited. A cross-sectional study was conducted to estimate the prevalence of F. tularensis in snowshoe hares, muskrats and coyotes in four regions of Québec, Canada, and to describe the risk of infection in relation to individual host (age, sex and body condition) and environmental characteristics. Between October 2012 and April 2013, 345 snowshoe hares, 411 muskrats and 385 coyotes were captured by trappers. Ecological characteristics of the location of capture were extracted from geographical databases. Prevalence of antibodies against F. tularensis (microagglutination test) was 2.9% in coyotes, 0.6% in hares and 0% in muskrats. F. tularensis DNA was not detected by real-time PCR in the pools of liver, kidney, lung and spleen from muskrats and hares but F. tularensis type AI was detected during testing of individual organs of two seropositive hares. Exact logistic regression analyses showed that age was a significant risk factor for seropositivity of coyotes, as were the proportion of forest and the proportion of area considered suitable for hares in the environment around the location of capture of the coyotes. The results of this study suggest the presence of the terrestrial cycle of F. tularensis in the regions studied.

Die genomische Insel (GI) FhaGI 1 des Stammes Francisella hispaniensis (Fhis) AS02 814 kann sowohl in die tRNAVal integriert als auch als episomale Form vorliegen und kodiert für einen putativen Prophagen. Im Rahmen dieser Arbeit konnte durch Verwendung synthetisch hergestellter, verkürzter Varianten von FhaGI-1 gezeigt werden, dass die GI auf andere Francisella Spezies übertragbar ist. Die ortsspezifische Integration und Exzision der GI sind Integrase-abhängige Prozesse, die durch weitere regulatorische Gene beeinflusst werden. Die Identifizierung der GI FphGI 1 in drei F. philomiragia-Stämmen zeigt, dass die tRNAVal als Integrationsort für GIs in Francisella dient. Die vermutlich nicht funktionale Integrase von FphGI 1 ist wahrscheinlich die Ursache für das Fehlen einer episomalen Form der GI. Das Vorhandensein von GIs in Francisella liefert einen Hinweis darauf, dass horizontaler Gentransfer zwischen verschiedenen Francisella Spezies möglich ist. Auf Grundlage von FhaGI 1 wurden zwei Varianten eines Francisella- Phagenintegrationsvektors (pFIV1-Val und pFIV2 Val) generiert. Der FIV Teil der Vektoren bildet eine zirkuläre, episomale Form, die nach der Transformation in verschiedene Francisella Spezies ortspezifisch in die tRNAVal integriert. Es konnte gezeigt werden, dass die Vektoren für die Expression von Reportergenen sowie die Komplementation von Francisella Deletionsmutanten geeignet sind. Sie sind sowohl in vitro als auch während der Infektion von Wirtszellen ohne Selektionsdruck stabil und zählen zu den low-copy-Vektoren. Damit erweitern die FIV-Vektoren das Repertoire der vorhandenen Werkzeuge zur genetischen Manipulation von Francisellen. Da der Stamm Fhis AS02 814 für Untersuchungen nicht zur Verfügung stand, wurde FhaGI 1 synthetisch in zwei Hälften hergestellt, die jedoch bisher nicht zusammengeführt werden konnten. Damit ist eine Aussage darüber, ob es sich bei FhaGI 1 tatsächlich um einen funktionalen Prophagen handelt, bis jetzt nicht möglich / The genomic island (GI) FhaGI 1 of strain Francisella hispaniensis (Fhis) AS02 814 can exist as a circular episomal form or integrated into the tRNAVal gene and codes for a putative prophage. In this work small-sized variants of FhaGI 1 were used to show that the GI can be transferred to other Francisella species. The site-specific integration and excision of the GI are integrase-dependent processes that are influenced by further regulatory genes. The identification of the GI FphGI 1 in three F. philomiragia strains shows that the tRNAVal gene serves as an integration site for GIs in Francisella. The integrase of FphGI 1 is probably non-functional and hence presumably the reason for the missing episomal form of the GI. The presence of GIs in Francisella might be an indication that horizontal gene transfer between different Francisella species could be possible. Two variants of a Francisella phage integration vector (pFIV1 Val and pFIV2 Val) were successfully constructed based on FhaGI 1. The FIV Val part of the vectors integrates site-specifically into the tRNAVal after transformation into different Francisella species. It was demonstrated that the vectors can be used for the expression of reporter genes as well as for the complementation of Francisella deletion mutants. They remain stable without selective pressure during in vitro growth and during the infection of host cells and fall into the group of low-copy-vectors. The FIV Val vectors expand the repertoire of tools that can be used for the genetic manipulation of Francisella. As strain Fhis AS02 814 could not be obtained for further analysis, FhaGI 1 was synthetically generated in two halves which could not be joined so far. Consequently, it is not possible to state whether FhaGI 1 actually codes for a functional prophage.

The lack of vaccines for emerging and re-emerging diseases highlights technical gaps and indicates a need for innovative approaches to produce new vaccines. Vaccines may be improved by knowledge of host responses to vaccination, disease pathogenesis, and the effect of age and genetics on vaccine outcome. This study's purpose was to quantitatively assess the molecular epidemiology of Francisella tularensis (Ft) and Venezuelan Equine Encephalitis Virus (VEEV). Study results support the Epidemiology Nexus model which holds that association of changes in gene expression to vaccination facilitate understanding the mechanisms of immune development and link public health and disease epidemiology. My research questions assessed the relationship between gene expression following vaccination, the relationship between age and vaccine response, and the association between Human Leukocyte Antigen (HLA) allele and vaccine response. The study was a novel secondary analysis of human data subjected to ANOVA to measure association between treatment and outcome, correlation to measure association of age with vaccine outcome, and Mann-Whitney U tests to measure association of HLA allele with vaccine outcome. Both Ft and VEEV vaccination elicited significant changes in gene expression. A highly positive relationship between age and vaccine outcome was shown for VEEV. The results may affect positive social change by contributing to a growing compendium of evidence of vaccine efficacy mechanisms that may function to assure the public of vaccine safety, combat vaccine hesitancy, and promote vaccine acceptance, as well as contribute mechanistic knowledge to reduce developmental costs of novel vaccines.

<p><i>Francisella tularensis</i> is a Gram-negative intracellular pathogen causing the zoonotic disease tularemia. <i>F. tularensis</i> can be found almost all over the world and has been recovered from several animal species, even though the natural reservoir of the bacterium and parts of its life cycle are still unknown. Humans usually get infected after handling infected animals or from bites of blood-feeding arthropod vectors. There are four subspecies of <i>F. tularensis</i>: the highly virulent <i>tularensis</i> (Type A) that causes a very aggressive form of the disease, with mortality as high as 60% if untreated, the moderately virulent <i>holarctica</i> (Type B) and <i>mediasiatica</i>, and the essentially avirulent subspecies <i>F. novicida</i>. So far, our knowledge of the molecular mechanisms that would explain these differences in virulence among the subspecies is poor. However, recent developments of genetic tools and access to genomic sequences have laid the ground for progress in this research field. Analysis of genome sequences have identified several regions that differ between <i>F. tularensis</i> subspecies. One of these regions, RD19, encodes proteins postulated to be involved in assembly of type IV pili (Tfp), organelles that have been implicated in processes like twitching motility, biofilm formation and cell-to-cell communication in pathogenic bacteria. While there have been reports of pili-like structures on the surface of <i>F. tularensis</i>, these have not been linked to the Tfp encoding gene clusters until now. Herein, I present evidence that the <i>Francisella</i> pilin, PilA, can complement pilin-like characteristics and promote assembly of fibers in a heterologous system in <i>Neisseria gonorrhoeae. pilA</i> was demonstrated to be required for full virulence of both type A and type B strains in mice when infected via peripheral routes. A second region, RD18, encoding a protein unique to <i>F. tularensis</i> and without any known function, was verified to be essential for virulence in a type A strain. Interestingly, the non-licensed live vaccine strain, LVS (Type B), lacks both RD18 and RD19 (<i>pilA</i>) due to deletion events mediated by flanking direct repeats. The loss of RD18 and RD19 is responsible for the attenuation of LVS, since re-introducing them <i>in cis</i> could restore the virulence to a level similar to a virulent type B strain. Significantly, these deletion events are irreversible, preventing LVS to revert to a more virulent form. Therefore, this important finding could facilitate the licensing of LVS as a vaccine against tularemia.</p>

Francisella tularensis is a Gram-negative intracellular pathogen causing the zoonotic disease tularemia. F. tularensis can be found almost all over the world and has been recovered from several animal species, even though the natural reservoir of the bacterium and parts of its life cycle are still unknown. Humans usually get infected after handling infected animals or from bites of blood-feeding arthropod vectors. There are four subspecies of F. tularensis: the highly virulent tularensis (Type A) that causes a very aggressive form of the disease, with mortality as high as 60% if untreated, the moderately virulent holarctica (Type B) and mediasiatica, and the essentially avirulent subspecies F. novicida. So far, our knowledge of the molecular mechanisms that would explain these differences in virulence among the subspecies is poor. However, recent developments of genetic tools and access to genomic sequences have laid the ground for progress in this research field. Analysis of genome sequences have identified several regions that differ between F. tularensis subspecies. One of these regions, RD19, encodes proteins postulated to be involved in assembly of type IV pili (Tfp), organelles that have been implicated in processes like twitching motility, biofilm formation and cell-to-cell communication in pathogenic bacteria. While there have been reports of pili-like structures on the surface of F. tularensis, these have not been linked to the Tfp encoding gene clusters until now. Herein, I present evidence that the Francisella pilin, PilA, can complement pilin-like characteristics and promote assembly of fibers in a heterologous system in Neisseria gonorrhoeae. pilA was demonstrated to be required for full virulence of both type A and type B strains in mice when infected via peripheral routes. A second region, RD18, encoding a protein unique to F. tularensis and without any known function, was verified to be essential for virulence in a type A strain. Interestingly, the non-licensed live vaccine strain, LVS (Type B), lacks both RD18 and RD19 (pilA) due to deletion events mediated by flanking direct repeats. The loss of RD18 and RD19 is responsible for the attenuation of LVS, since re-introducing them in cis could restore the virulence to a level similar to a virulent type B strain. Significantly, these deletion events are irreversible, preventing LVS to revert to a more virulent form. Therefore, this important finding could facilitate the licensing of LVS as a vaccine against tularemia.

Francisella tularensis, the causative agent of tularemia, is a potent human and animal pathogen. Initially upon infection of the host, intramacrophage proliferation of F. tularensis occurs but after activation of the acquired host immunity, the phagocytes become activated to kill the bacterium. In my thesis, I focused on mechanisms utilized by F. tularensis to survive intracellularly and on host mechanisms responsible for macrophage-mediated killing and control of infection. The F. tularensis-specific protein IglC has been previously shown to be essential to the intramacrophage proliferation and virulence of the bacterium in mice. By electron microscopy of macrophages infected with either the live vaccine strain of F. tularensis or an isogenic mutant, denoted ∆iglC, expression of IglC was found to be necessary for the bacterium to escape from the phagosome. IFN-g-activated macrophages significantly inhibited the escape of the live vaccine strain of F. tularensis from the phagosome. iNOS and phox generate NO and O2-, respectively. These molecules and their reaction products possess both bactericidal and immunoregulatory properties. We investigated the capability of IFN-g-activated peritoneal exudate cells from gene deficient iNOS-/- or p47phox-/- mice to control an intracellular F. tularensis LVS infection. iNOS was found to contribute significantly to the IFN-g induced killing, while phox contributed only to a minor extent. Unexpectedly, bacteria were eradicated even in the absence of both a functional phox and an active iNOS. The eradication was found to depend on ONOO-, the reaction product of NO and O2-, because addition of a decomposition catalyst of ONOO- completely inhibited the killing. Studies on iNOS-/- or p47phox-/- mice infected with F. tularensis LVS showed phox to be important during the first days of infection, a stage when iNOS seemed dispensable. Eventually, iNOS-/- mice died of the infection, suggesting a role of iNOS later in the course of infection. iNOS-/- mice exhibited elevated IFN-g serum levels and severe liver damage suggesting that the outcome of infection was at least in part related to an uncontrolled immune response. Several pathogenic bacteria express Cu,Zn-SOD, which in combination with other enzymes detoxifies reactive oxygen species produced by the host. A deletion mutant of F. tularensis LVS lacking the gene encoding Cu,Zn-SOD was attenuated at least 100-fold compared to LVS in mice. In peritoneal exudate cells from mice, Cu,Zn-SOD was found to be required for effective intramacrophage proliferation and, in mice, important for bacterial replication at the very early phase of infection. In summary, the most conspicuous findings were a capability of IFN-g activated macrophages to retain F. tularensis LVS in the phagosome, an essential role of ONOO- in intracellular killing of F. tularensis, and an importance of Cu,Zn-SOD to the virulence of F. tularensis LVS.

Francisella tularensis, agent étiologique de la tularémie, est un pathogène intracellulaire facultatif capable d'infecter de nombreuses cellules de mammifères. Pour se multiplier activement dans le cytoplasme des cellules hôtes, la bactérie doit être en mesure de capter dans cet environnement tous les composés nécessaires à son métabolisme, et notamment des acides aminés qui représentent ses principales sources de carbone et d'azote. Les pathogènes à multiplication intracellulaire ont mis en place un ensemble de mécanismes, visant i) la manipulation des voies métaboliques de l'hôte, pour accroître le pool de nutriments disponibles, et ii) l'expression de transporteurs dédiés, pour la captation optimale de ces nutriments. Cet ensemble de mécanismes est regroupé sous le terme de " virulence nutritionnelle ". Chez Legionella pneumophila, plusieurs membres d'une sous-famille de transporteurs actifs secondaires (désignés Pht, ou transporteurs phagosomaux), responsables de la captation des acides aminés lors de la phase intracellulaire de la bactérie, ont été caractérisés. Dans ce travail, nous avons établi le rôle de deux membres de la sous-famille des transporteurs Pht (désignés AnsP et IleP), dans le transport d'acides aminés et la virulence de Francisella. La protéine AnsP est un transporteur d'asparagine. La délétion du gène codant pour ce transporteur n'a pas d'effet sur la croissance de Francisella en milieu synthétique, mais entraîne une diminution drastique de sa multiplication intracellulaire dans tous les types cellulaires testés, ainsi qu'une atténuation importante de la virulence chez la souris. La perte de virulence du mutant asnP est réversible aussi bien in vivo qu'in vitro par ajout d'asparagine en excès. F. tularensis, qui est prototrophe pour l'asparagine en milieu minimum, devient donc auxotrophe dans le cadre de sa croissance intracellulaire, et nécessite un transport de cet acide aminé via AnsP. Ce changement de besoins en asparagine entre le milieu extérieur et le milieu intracellulaire illustre bien le phénomène d'adaptation nutritionnel que réalise la bactérie dans le cadre d'une infection. La délétion du second transporteur, IleP, entraine un défaut de croissance en milieu minimum, réversible par ajout de thréonine, un précurseur métabolique de l'isoleucine chez F. tularensis subsp. novicida. Des expériences d'incorporation d'isoleucine marquée ont permis de mettre en évidence la fonction de transporteur d'isoleucine de la protéine IleP. La délétion du gène codant pour IleP entraine également un défaut de multiplication in vitro, associé à un léger retard de sortie du phagosome ainsi qu'une atténuation importante de la virulence chez la souris. Ce transporteur assure donc la captation de l'isoleucine dans des conditions où l'utilisation de la thréonine, ne permet pas d'assouvir les besoins de la bactérie. De façon remarquable, la voie de biosynthèse de l'isoleucine via la thréonine est interrompue chez les sous-espèces tularensis et holarctica. La croissance de ces sous espèces, plus virulentes que novicida, dans la cellule infectée devient donc strictement dépendante du transport de l'isoleucine par IleP. Cet exemple constitue une parfaite illustration de la spécialisation des souches pathogènes aux conditions nutritionnelles de leur hôte. En conclusion, l'ensemble des travaux présentés dans cette thèse a permis de démontrer la participation de deux transporteurs d'acides aminés à la virulence nutritionnelle de la bactérie Francisella.

Francisella tularensis is a highly virulent, intracellular pathogen that causes the disease tularaemia. Francisella species contain a cluster of genes referred to as the Francisella pathogenicity island (FPI). Several genes contained in the FPI encode proteins needed for the intracellular growth and virulence of Francisella tularensis. Pathogenicity determinant protein A (PdpA), encoded by the pdpA gene, is located within the FPI and has been associated with the virulence of Francisella species. The experiments outlined in this dissertation examine the properties of PdpA protein expression and localization as well as the phenotypes of non-polar F. novicida pdpA mutants. Monoclonal antibody detection of PdpA showed that it is a soluble protein that is upregulated in iron-limiting conditions and undetectable in an mglA or mglB mutant background. Deletion of pdpA resulted in a strain that was highly attenuated for virulence in chicken embryos and mice. The ΔpdpA strain was capable of a small amount of intracellular replication but, unlike wild-type F. novicida, remained associated with the lysosomal marker LAMP-1, suggesting that PdpA is necessary for progression from the early phagosome phase of infection. Infection of macrophages with the ΔpdpA mutant generated a host-cell mRNA profile distinct from that generated by infection with wild type F. novicida. The transcriptional response of the host macrophage indicates that PdpA functions directly or indirectly to suppress macrophage ability to signal via growth factors, cytokines and adhesion ligands. Experiments were designed to mutagenize a putative F-box domain within the amino terminus of PdpA. Deletion of amino acids 112-227 created a strain which was impaired in intracellular replication and exhibited severely reduced virulence. However, alanine mutagenesis of key conserved leucine residues required for the interaction of F-box domains with host proteins had no observed effect on bacterial growth in macrophages and did not affect virulence in chicken embryos or mice. Mono and polyubiquitinated proteins associated with both the wild type F. novicida and ΔpdpA bacterial strains early during the infection of J774A.1 macrophages. After 1 hour of infection the wild type strain developed a more intimate association with mono and polyubiquitinated proteins whereas the ΔpdpA strain did not. Inhibition of the host cell proteasome during infection did not affect the intracellular growth of wild type F. novicida. PdpA research concludes by examining the secretion patterns of F. novicida. PdpA was not detected as a surface exposed protein using biotinylation whereas IglA, IglB and IglC were found to be surface exposed in both wild type and ΔpdpA backgrounds. These observations suggest that PdpA is not involved in the assembly or function of the Francisella secretion system. FLAG tagged PdpA protein could not be detected in the TCA precipitated supernatant of broth grown cultures or in the immunoprecipitated cytosol of infected macrophages suggesting that PdpA is not a secreted protein.