Yersinia pestis, the gram-negative causative agent of plague, is a master of immune evasion. The bacterium possesses a type three secretion system which translocates Yop effector proteins into host immune cells to inhibit a number of immune and cell signaling cascades. Interestingly, this apparatus is not expressed at low temperatures such as those found within the flea vector and is therefore neither in place nor functional when the bacteria are first transmitted into a mammalian host. However, the bacterium is still able to avoid activating the immune system, even very early during infection. When grown at 37°C (human body temperature) Y. pestis produces a tetra-acyl lipid A molecule, which is antagonistic to the human Toll like receptor 4/MD2, the major lipopolysaccharide recognition receptor. Although tetra-acyl lipid A binds this receptor complex, it does not induce signaling, and in fact inhibits the receptors interaction with other stimulatory forms of lipid A. The work undertaken in this thesis seeks to determine if the production of tetra-acyl lipid A by Y. pestis is a key virulence determinant and was a critical factor in the evolution of Y. pestis from its ancestral parent Yersinia pseudotuberculosis. By examining the enzymes involved in the lipid A biosynthesis pathway, it has been determined that Y. pestis lacks LpxL, a key enzyme that adds a secondary acyl chain on to the tetra acyl lipid A molecule. In the absence of this enzyme, Y. pestis cannot produce a TLR4 stimulating form of lipid A, whereas Y. pseudotuberculosis does contain the gene for LpxL and produces a stimulatory hexa acyl lipid A. To determine if the absence of LpxL in Y. pestis is important for virulence, LpxL from E. coli and Y. pseudotuberculosis were introduced into Y. pestis. In both cases the addition of LpxL led to bacterium which produced a hexa-acylated lipid A molecule and TLR4/MD2 stimulatory LPS. To verify the LpxL phenotype, lpxL was deleted from Y. pseudotuberculosis, resulting in bacteria which produce tetra-acylated lipid A and nonstimulatory LPS. Mice challenged with LpxL expressing Y. pestis were found to be completely resistant to infection. This profound attenuation in virulence is TLR4 dependent, as mice deficient for this receptor rapidly succumb to disease. These altered strains of the bacterium also act as vaccines, as mice infected with Y. pestis expressing LpxL then challenged with wild type Y. pestis do not become ill. These data demonstrate that the production of tetra-acyl lipid A is a critical virulence determinant for Y. pestis, and that the loss of LpxL formed a major step in the evolution of Y. pestis from Y. pseudotuberculosis. These bacterial strains were also used as tools to determine the contributions of different innate immune receptors and adaptor molecules to the host response during Y. pestis infection. The use of LpxL expressing Y. pestis allowed identification of the innate immune pathways critical for protection during Y. pestis infection. This model also established that CD14 recognition of rough LPS is critical for protection from Y. pestisexpressing LpxL, and activation of the IL-1 receptor and the induction of IL-1β plays a major role in this infection as well. The lipid A acylation profile of gram negative bacteria can have a direct and profound effect on the pathogenesis of the organism. This work illustrates a previously unknown and critical aspect of Y. pestis pathogenesis, which can be extended to other gram-negative pathogens. The greater detail of the contributions which different host adaptor and receptor molecules make to the overall innate immune signaling pathway will allow a better insight into how gram negative infections progress and how they are counteracted by the immune system. Alterations of the lipid A profile of Y. pestis have important implications for the production of vaccines to Y. pestis and other gram negative pathogens. Taken together, this work describes a novel mechanism for immune evasion by gram negative bacteria with consequences for understanding the immune response and the creation of more effective vaccines, both of which will decrease the danger posed by this virulent pathogen.

Yersinia pestis, the causative agent of plague, specializes in causing dense bacteremia following intradermal deposition of a small number of bacteria by the bite of an infected flea. This robust invasiveness requires the ability to evade containment by the innate immune system. Of the various mechanisms employed by Y. pestis to subvert the innate immune response and to proliferate rapidly in mammalian tissue, only a few are well-characterized. Here, I present two complementary genetic analyses of Y. pestis adaptations to the mammalian environment. In the first, genome-wide fitness profiling for Y. pestis by Tn-seq demonstrates that the bacterium has adapted to overcome limitation of diverse nutrients during mammalian infection. In the second, a series of combinatorial targeted mutations disentangles apparent functional redundancy among the effectors of the Y. pestis type III secretion system, and we report that YpkA, YopT, and YopJ contribute to virulence in mice. We have also begun to investigate a novel relationship between Y. pestis and mammalian platelets, a highly abundant cell type in plasma. I present evidence that Y. pestis has evolved specific mechanisms to interfere with platelet activation, likely in order to evade immune responses and promote maintenance of bacteremia by undermining platelet thrombotic and innate immune functions. The principles guiding this work – systematic genetic analysis of complex systems, coupled with rational modification of in vitro assays to more closely mimic the in vivo environment – are a generalizable approach for increasing the efficiency of discovering new virulence determinants in bacterial pathogens.

<p>This dissertation discusses molecular analyses of dental and skeletal material from victims of the Black Death with the goal of both identifying and describing the evolutionary history of the causative agent of the pandemic. Through this work, <em>Yersinia pestis</em> DNA was successfully identified in skeletal material from a well-documented Black Death burial ground, the East Smithfield cemetery of London, England (1348 -1350). The thesis presents two major methodological advancements in the field of ancient pathogen research: 1) it describes a protocol to confirm the authenticity of ancient pathogen DNA, thus circumventing tenuous issues relating to modern contaminants, and 2) it demonstrates the applicability of DNA capture methods to isolate ancient pathogen DNA from its complex metagenomic background common to ancient DNA extracts. The dissertation is comprised of three publications. The first, submitted to the journal BMC Systems Biology, describes a computational software program for oligo design that has applications to PCR, and capture techniques such as primer extension capture (PEC) and array-based capture. The second manuscript, published in the Proceedings of the National Academy of Sciences, presents a novel capture technique for retrieval of the <em>pestis</em>-specific pPCP (9.6kb) plasmid which can be used as a simple screening tool for the presence of <em>Y. pestis</em> DNA in ancient remains, and describes a method for authenticating ancient pathogen DNA. The third paper, published in the journal Nature, presents a draft genome of <em>Yersinia pestis </em>isolated from the individuals of the East Smithfield collection, thus presenting the first ancient pathogen genome in published literature. Evolutionary changes as they relate to phylogenetic placement and the evolution of virulence are discussed within an anthropological framework.</p> / Doctor of Philosophy (PhD)

Avec l'augmentation des menaces asymétriques partout sur la planète depuis le début des années 1990s impliquant des armes produisant de forts dommages par rapport à leurs coûts, plusieurs types d'armes biologiques sont devenus une menace d'importance croissante dans le théâtre militaire ainsi que dans le monde civil. Les armes biologiques peuvent êtres facilement dissimulées sur une personne. Elles sont difficilement détectables et leurs déploiements peuvent causer des dommages psychologiques incommensurables sur les populations affectées, assmant un ravage souvent loin au delà de leur emplacement physique. Pour essayer de diminuer l'efficacité de ces armes, des méthodes pour détecter et distinguer en retrait les agents biologiques parmi les autres aérosols naturels présents dans l'atmosphère sont actuellement en développement. Recherche et Développement pour la Défense Canada (RDDC) et le gouvernement du Canada explorent actuellement les LIDARs comme la technologie principale visant la détection à distance d'organismes biologiques. Toutes informations pouvant êtres récoltées à propos des armes biologiques en utilisant cette technologie sont utiles à l'avancement de la cause de la biodétection à distance. Ce rapport présente les résultats d'un projet ayant pom but de décrire les effets de l'âge des bactéries sur leurs propriétés spectrales de fluorescence en utilisant la technologie LIDAR. Les expériences ont été exécutées dans une chambre hermétique LIDAR de laboratoire sur des simulants d'agents biologiques connues, trois desquelles (2 souches de Bacillus subtilis var. niger identifiées comme BGnew et BGold et une souche de Bacillus thuringiensis identifié comme BT) étant des simulants de la bactérie Bacillus anthracis (l'anthrax), sans doute l'agent biologique le plus probable à être utilisé, et l'autre (Erwinia herbicola identifié comme EH) étant un simulant de Yersinia pestis (la peste). Les bactéries étaient mélangées avec leur milieu de culture, soit le ± Tryptic soy broth ¿ (TSB). Bien que plus de tests soient nécessaires afin de pouvoir finaliser des conclusions plus robustes, certaines tendances ont été observées. Le mélange de Erwinia herbicola a montré une fluorescence induite ayant une tendance vers les courtes longueurs d'ondes lorsque la culture était plus âgée. Le mélange de Bacillus thuringiensis (BT) a démontré une petite tendance vers les longues longueurs d'ondes avec l'âge. Les deux différentes souches de Bacillus globigii ont montrées des fluorescences induites ayant des tendances vers les courtes longueurs d'ondes après un mois et vers les longues longueurs d'ondes après trois mois. En bref, la signature de fluorescence semble dépendre de l'âge du mélange bactérie-bouillon de culture bien que cet effet varie en fonction du type mélange. Certains mélanges étaient plus efficaces à produire de la fluorescence que d'autres. Le mélange de BGnew-ljour a démontré la plus haute efficacité de fluorescence tandis que BG_old-3mois, BGold-ljour et EH-ljour ont démontrés les plus faibles. Nos résultats démontrent que la signature spectrale d'une bactérie est influencée par le temps d'incubation dans son milieu de culture. Cette information est très importante lors de l'élaboration de banques de signatures standardisées servant à la classification bactérienne à distance dans le cadre d'intervention sur le terrain. Dans des contextes militaires et de sécurité publique, cette information serait aussi un outil important pour retrouver l'origine des agents biologiques (ex: s'ils parviennent d'un labo ou d'un lieu d'entreposage).

Génératrice depuis le VIe siècle de notre ère de crises épidémiques récurrentes en Occident, la peste a profondémentmarqué l’histoire des sociétés européennes, tant sur le plan biologique que culturel, économique et politique. Sil’histoire des épidémies qu’elle a engendrées est aujourd’hui relativement bien connue, un certain nombre de questionssur ses caractéristiques épidémiologiques passées demeurent pour partie irrésolues. En particulier, le caractère sélectifou non de la mortalité par peste à l’égard de l’âge, du sexe et de l’état de santé préexistant des individus faitactuellement débat. À partir d’une approche anthropobiologique, le présent travail se propose de contribuer à cettediscussion. Il livre les résultats de l’étude d’un corpus de 1090 squelettes provenant, d’une part, de quatre sitesd’inhumation de pestiférés de la fin du Moyen Âge et du début de l’époque moderne et, d’autre part, de deuxcimetières paroissiaux médiévaux utilisés hors contexte épidémique. Cette étude révèle en premier lieu l’existenced’une signature démographique commune aux séries en lien avec la peste. Leur composition par âge et par sexe,distincte de celle caractérisant la mortalité naturelle, est au contraire en adéquation avec la structure théorique d’unepopulation vivante préindustrielle. L’examen de divers indicateurs de stress suggèrent par ailleurs que les victimes dela peste jouissaient, à la veille de leur décès, d’un meilleur état de santé que les individus morts en temps normal. Lesrésultats obtenus concourent à démontrer que les facteurs causals de ces lésions squelettiques, d’accoutuméresponsables d’une diminution des chances de survie, n’eurent au contraire qu’une influence mineure, si ce n’est nulle,sur le risque de mourir de l’infection à Yersinia pestis. Ce travail livre in fine un faisceau d’arguments convergents quitendent à prouver que les épidémies de peste anciennes furent à l’origine d’une mortalité non sélective, la maladiefrappant indistinctement les individus des deux sexes, de tous âges et de toutes conditions sanitaires. / From the 6th century onwards, plague caused recurring mortality crises in the Western world. Such epidemics hadprofound biological, cultural, economic and political impacts on European societies. Some aspects of the history ofplague epidemics are currently well known, but many questions remain unanswered, such as the preciseepidemiological pattern of the disease in ancient times. It is unclear whether plague killed people indiscriminately orwhether this disease was selective with respect to age, sex and health. This research contributes to this debate.It consists of an anthropological and paleopathological study of skeletal remains of 1090 individuals, including plaguevictims from four medieval and post-medieval burial grounds, and individuals from two parochial cemeteries in useduring periods of normal mortality. Results from the four plague-related assemblages reveal a peculiar demographicsignature. Age and sex distribution differs clearly from what is expected in non-epidemic periods, when it is shown tocorrespond closely to the demographic structure of the living population. Moreover, the study of various non-specificskeletal stress markers shows that plague victims were in a better health before they passed away than people who diedin non-epidemic periods. The results demonstrate that individuals who suffered stress and disease had a reducedchance of survival in non-epidemic periods, whereas they were not at a higher risk to die during plague epidemics.This study provides evidence that plague was not selective, and that it killed regardless of sex, age, and pre-existing health.

Of the eleven species of bacteria that comprise the genus Yersinia of the family Enterobacteriaceae, three species are pathogenic for humans. Yersinia pseudotuberculosis and Yersinia enterocolitica usually cause a mild, self-limiting mesenteric lymphadenitis or ileitis. Yersinia pestis causes a highly invasive often fatal disease known as plague. All three elaborate a type three secretion system that is essential for virulence and encoded on closely related plasmids. In Y. pestis, all the effectors, structural components and chaperones are encoded on the 70kb plasmid, pCD1. Of these, LcrV from Y. enterocolitica has been implicated in playing an immunosuppressive role through its interaction with host Toll-like receptor 2 (TLR2) and induction of IL-10. Through expression and purification of recombinant LcrV from Escherichia coliwe show that only high molecular weight species of rLcrV are able to stimulate TLR2. In a highly sensitive subcutaneous mouse infection model we demonstrate no difference in the time to death between TLR2-sufficient or deficient mice. Analysis of cytokine levels between these two genotypes also shows no significant difference between splenic IL-10 and IL-6 or levels of bacteria. We conclusively show that this interaction, if it does occur, plays no significant role in vivo. In a separate set of experiments, we also determined that the expression of F1, a peptide shown to be responsible for 37°C-dependent inhibition of invasion by Y. pestis in vitro, was significantly decreased under high oxygen conditions. This led us to re-examine the invasion phenotype both in vitro and in vivo. These results give new insights into virulence gene expression in Y. pestis by environmental cues other than temperature.

Yersinia pestis (Y. pestis), as the causative agent of plague, has caused deaths estimated to more than 200 million people in three historical plague pandemics, including the infamous Black Death in medieval Europe. Although infection with Yersinia pestis can mostly be limited by antibiotics and only 2000-5000 cases are observed worldwide each year, this bacterium is still a concern for bioterrorism and recognized as a category A select agent by the Centers for Disease Control and Prevention (CDC). The investigation into the host-pathogen interactions during Y. pestis infection is important to advance and broaden our knowledge about plague pathogenesis for the development of better vaccines and treatments. Y. pestis is an expert at evading innate immune surveillance through multiple strategies, several mediated by its type three secretion system (T3SS). It is known that the bacterium induces rapid and robust cell death in host macrophages and dendritic cells. Although the T3SS effector YopJ has been determined to be the factor inducing cytotoxicity, the specific host cellular pathways which are targeted by YopJ and responsible for cell death remain poorly defined. This thesis research has established the critical roles of caspase-8 and RIP kinases in Y. pestis-induced macrophage cell death. Y. pestis-induced cytotoxicity is completely inhibited in RIP1-/- or RIP3-/-caspase-8-/- macrophages or by specific chemical inhibitors. Strikingly, this work also indicates that macrophages deficient in either RIP1, or caspase-8 and RIP3, have significantly reduced infection-induced production of IL-1β, IL-18, TNFα and IL-6 cytokines; impaired activation of NF-κB signaling pathway and greatly compromised caspase-1 processing; all of which are critical for innate immune responses and contribute to fight against pathogen infection. Y. pestis infection causes severe and often rapid fatal disease before the development of adaptive immunity to the V bacterium, thus the innate immune responses are critical to control Y. pestis infection. Our group has previously established the important roles of key molecules of the innate immune system: TLR4, MyD88, NLRP12, NLRP3, IL-18 and IL-1β, in host responses against Y. pestis and attenuated strains. Yersinia has proven to be a good model for evaluating the innate immune responses during bacterial infection. Using this model, the role of caspase-8 and RIP3 in counteracting bacterial infection has been determined in this thesis work. Mice deficient in caspase-8 and RIP3 are very susceptible to Y. pestis infection and display reduced levels of pro-inflammatory cytokines in spleen and serum, and decreased myeloid cell death. Thus, both in vitro and in vivo results indicate that caspase-8 and RIP kinases are key regulators of macrophage cell death, NF-κB and caspase-1 activation in Yersinia infection. This thesis work defines novel roles for caspase-8 and RIP kinases as the central components in innate immune responses against Y. pestis infection, and provides further insights to the host-pathogen interaction during bacterial challenge.

Ausgehend von dem geschichtlichen Pestausbruch des 14. Jahrhunderts in Europa werden 350 Jahre Geschichte der Pest als Pandemie, Epidemie, Endemie und Pest der Kinder in Deutschland, dem Kurfürstentum Sachsen und der Residenzstadt Dresden mit dem Amt Radeberg untersucht und dargestellt. Wichtig war dabei die Herausstellung, dass Pandemien durchaus die Welt verändern und der „Krieg der Mikroben, als sogenannte „Unsichtbare Feinde”, Zivilisationen immer wieder mit ihren eingefahrenen Strukturen zum Wanken bringen können. Dokumentiert wird die Sterbensgefahr durch die Pestausbrüche und deren Überlieferung in Dresdner Akten und dem Amt Radeberg, welches auch zum Fluchtort der Kurfürsten bei Pestgefahr wurde. Herausgearbeitet wurde ebenfalls die stetige Pestgefahr, die als Bedrohung durch das nahe Grenzgebiet von Böhmen ausging, durch Glaubensflüchtlinge beziehungsweise mit dem Handel auf dem Wasser- oder Landwege nach Sachsen gebracht oder durch die Heerscharen des Dreißigjährigen Krieges verbreitet wurde. Nachdem die Pest 1682 offiziell als „überwunden“ erklärt wurde, traten bis in die Jetztzeit immer wieder epidemische oder endemische Pestausbrüche auf, die zeigen - die Pest lebt weiter…