Sous des conditions de croissance particulières, certaines bactéries sont capables d'entrer en état de « compétence » pour la transformation naturelle, c'est-à-dire d'exprimer un ensemble de gènes nécessaires à la mise en place d'un système d'import d'ADN exogène dont l'intégration conduit à une transformation génétique et phénotypique. C'est le cas de Legionella pneumophila, bactérie environnementale et agent étiologique de la légionellose. La transformation naturelle a potentiellement participé à l'évolution du génôme de L. pneumophila.Ainsi, l'objectif premier de cette thèse était de décrire les composants principaux du système de transformation naturelle de L. pneumophila, ainsi que son activation et rôle potentiel dans la relation de la bactérie avec ses hôtes. Des méthodes d'analyse transcriptomique et de mutagénèse dirigée ont permis d'identifier les principaux gènes impliqués dans la mise en place du système de transformation naturelle qui, de façon cohérente avec un rôle adaptatif, ne semble pas impliqué dans la virulence bactérienne. Le système inclut un pilus de transformation, structure fréquemment observée chez les espèces naturellement transformables. Le rôle de la protéine structurale MreB dans le mécanisme de transformation naturelle a également été étudié. En proposant un premier modèle du système de transformation naturelle de L. pneumophila, ces travaux ouvrent la voie à une analyse plus détaillée de la dynamique du système et, plus généralement, à une meilleure compréhension des mécanismes de la transformation naturelle chez les bactéries Gram-négatives / Under certain growth conditions, some bacteria are able to develop a « competence » state for natural transformation, that is, to express a panel of genes involved in the assembly of a DNA uptake system that allows bacteria to take up and recombine free exogenous DNA, leading to a genetic and phenotypic transformation. Natural transformation may have played a role in the evolution of the L. pneumophila genome.Thus, the main objective of this work was to describe the main components of the L. pneumophila DNA uptake system and to investigate its role regarding the host-pathogen interaction. Transcriptomic analysis and directed mutagenesis permitted to identify the main components of the system which is not involved in bacterial virulence. The system include a transformation pilus that is a structure frequently found in transformable species. The role of the structural protein MreB has also been investigated.By describing a first model of the natural transformation system of L. pneumophila, this work paves the way to a deeper analysis of the system dynamics and, more generally, to a better understanding of natural transformation in Gram-negative species

Des souches de Vibrio appartenant au clade Splendidus sont retrouvées de manière récurrente lors des mortalités estivales d'huîtres juvéniles. La souche V. tasmaniensis LGP32 est un pathogène intracellulaire facultatif des hémocytes d'huître, dont elle altère les fonctions de défense. Nous montrons ici que LGP32 se comporte comme un pathogène intravacuolaire qui survit au sein de larges vacuoles intrahémocytaires. Il induit des effets cytopathiques tels qu'une perméabilisation membranaire et un lessivage du contenu cytosolique des hémocytes. Cette cytotoxicité est dépendante de l'invasion hémocytaire. Par ailleurs, à l'intérieur du phagosome, LGP32 sécrète des vésicules de membrane externe (OMVs). Chez LGP32, ces OMVs jouent un rôle protecteur contre les défenses de l'hôte et servent de véhicules pour la délivrance de facteurs de virulence aux cellules de l'hôte. En effet, elles sont capables de titrer les peptides antimicrobiens et présentent un fort contenu en hydrolases (25% du protéome des OMVs). Une sérine protéase, nommée Vsp car elle est uniquement sécrétée par voie vésiculaire participe à la virulence de LGP32 en infections expérimentales mais ne dégraderait pas les peptides antimicrobiens. Par une approche transcriptomique, nous avons identifié une série de gènes impliqués dans la réponse anti-oxydante et l'efflux de cuivre, qui sont surexprimés dans les stades intracellulaires précoces de LGP32. La génomique fonctionnelle a montré que ces deux fonctions importantes sont requises pour la survie intracellulaire, la cytotoxicité et la virulence de LGP32. Leur grande conservation parmi les vibrios laisse supposer qu'elles puissent contribuer à la survie intracellulaire d'autres espèces de Vibrio. / Vibrio strains belonging to the Splendidus Clade have been repeatedly found in juvenile diseased oysters affected by summer mortalities. V. tasmaniensis LGP32 is an intracellular pathogen of oyster hemocytes which has been reported to alter the oxidative burst and inhibit phagosome maturation. We show here that LGP32 behaves as an intravacuolar pathogen that survives within large cytoplasmic vacuoles. LGP32 induces cytotoxic effects such as membrane disruptions and cytoplasmic disorders. Cytotoxicity was shown to be entirely dependent on LGP32 entry into hemocytes. Moreover, LGP32 releases outer membrane vesicles (OMVs) inside the phagosome. LGP32 OMVs were found to be protective against host defenses and to serve as vehicles for the delivery of LGP32 virulence factors to oyster immune cells. Indeed, OMVs conferred a high resistance to antimicrobial peptides. They also displayed a high content in hydrolases (25 % of total proteome) among which a serine protease, named Vsp for vesicular serine protease, was found to be specifically secreted through OMVs. Vsp was shown to participate in the virulence phenotype of LGP32 in oyster experimental infections but did not degrade AMPs entrapped in OMVs. By developing a transcriptomic approach, we identified a series of Vibrio antioxidant and copper efflux genes whose expression is strongly induced within oyster hemocytes. Construction of isogenic deletion mutants showed that resistance to reactive oxygen species and copper efflux are two important functions required for LGP32 intracellular survival, cytotoxic effects and virulence. Their high conservation among vibrios suggests they could contribute to intracellular survival of other Vibrio species.

Listeria monocytogenes est un pathogène intracellulaire facultatif responsable d’une infection sévère d’origine alimentaire, la listériose. L’étude du processus d’infection cellulaire de cette bactérie a permis d’élucider divers mécanismes impliqués dans les interactions hôte-pathogène et dans le fonctionnement de la cellule eucaryote. En particulier, L. monocytogenes a été l’un des modèles pionniers dans la découverte du ciblage de la chromatine et de régulateurs nucléaires par des microbes. L’étude d’un facteur de virulence de L. monocytogenes, LntA, a permis l’identification d’un de ces régulateurs : BAHD1. En recrutant des protéines impliquées dans la formation de l’hétérochromatine, telles HDAC1/2 et HP1, BAHD1 stimule la formation d’une chromatine compacte à effet répressif. Lors d’une infection de cellules épithéliales par L. monocytogenes, BAHD1 réprime la réponse immunitaire stimulée par les interférons, une fonction inhibée par LntA. BAHD1 demeurant peu étudiée, mon doctorat a eu pour premier objectif de poursuivre la caractérisation de ce régulateur épigénétique. Par ailleurs, des données préliminaires suggéraient qu’un facteur de virulence de Listeria récemment découvert, InlP, avait la potentialité d’être, comme LntA, une nucléomoduline. Mon deuxième objectif a été d’explorer cette hypothèse.Les résultats de mon premier axe montrent que BAHD1 interagit avec MIER1 et que cette interaction est cruciale pour l’association de BAHD1 aux HDAC1/2. Nous reportons également que BAHD1 modifie la chromatine en changement la méthylation et l’acétylation des histones, ainsi que la méthylation de l’ADN, au niveau d’un gène cible, ESR1. Ces résultats nous permettent de proposer que BAHD1 forme, avec MIER1, un échafaudage assemblant un nouveau complexe de remodelage de la chromatine associé aux HDAC1/2 : le complexe BAHD1. Nous avons ensuite étudié un rôle de BAHD1 dans un organe ciblé par la Listeria, le cerveau. Nos résultats indiquent qu’une déficience totale en BAHD1 altère le transcriptome global de cet organe chez la souris. Les gènes majoritairement surexprimés sont impliqués dans des fonctions du système nerveux, le métabolisme et des troubles neurologiques. Les gènes majoritairement sous-exprimés sont impliqués dans des voies de l’immunité innée, dont des gènes de réponses aux interférons. Par ailleurs, une haplo-déficience en Bahd1 provoque des troubles comportementaux. En comparaison des souris Bahd1+/+, les souris Bahd1+/- souffrent d’une anxiété accrue et d’altérations du réflex de sursaut acoustique. Ces résultats suggèrent qu’une dérégulation de BAHD1, par des stimuli de l’environnement ou par des stimuli infectieux, pourrait avoir des effets neuro-pathologiques.Le second axe de ma thèse concernait l’étude des interactions d’InlP avec des protéines nucléaires de l’hôte, identifiées par un crible double-hybride. Nous montrons d’abord qu’InlP est une internaline atypique, avec des répétitions riches en leucine caractérisées par un motif LPX2. Nous identifions, ensuite, deux protéines nucléaires ciblées par InlP : le facteur d’épissage et suppresseur de tumeur RBM5 et le corépresseur RERE. Quand InlP est produite de façon ectopique dans les cellules humaines, elle se localise dans le noyau, où elle altère la formation de corps nucléaires enrichis en RERE. Dans des cellules sur-exprimant RBM5, InlP inhibe l’effet pro-apoptotique de RBM5 et stimule la formation de corps nucléaires denses associés à RBM5. Ces résultats suggèrent qu’InlP est une nucléomoduline agissant sur la l’assemblage et le désassemblage de compartiments de stockage de protéines cibles impliquées dans la synthèse et l’épissage d’ARNs de l’hôte.Ce travail ouvrent des perspectives dans la compréhension des interactions hôte-pathogène et dans une meilleure connaissance des mécanismes patho-épigénétiques, ainsi qu’en biologie cellulaire, dans la compréhension de la dynamique des organites nucléaires sans membrane. / Listeria monocytogenes is an optional intracellular pathogen responsible for a severe foodborne infection called listeriosis. The study of the cellular infection process of this bacterium has shed light on various mechanisms involved in host-pathogen interactions and in the functioning of the eukaryotic cell. In particular, L. monocytogenes has emerged as one of the pioneering models in the discovery of microbial targeting of chromatin and nuclear regulators. The study of a virulence factor of L. monocytogenes, LntA, allowed the identification of one of these regulators : BAHD1. By recruiting proteins involved in the formation of heterochromatin, such as HDAC1/2 and HP1, BAHD1 stimulates the formation of a compact chromatin with a repressive effect. When epithelial cells are infected with L. monocytogenes, BAHD1 suppresses the immune response stimulated by interferons, a function inhibited by LntA. Since BAHD1 is still under-researched, the first objective for my thesis was to further characterize this epigenetic regulator. In addition, preliminary data suggested that a recently discovered virulence factor of Listeria, InlP, had the potential to be, like LntA, a nucleomodulin. My second objective was to explore this hypothesis.The results of my first axis show that BAHD1 interacts with MIER1 and that this interaction is crucial for the association of BAHD1 with HDAC1/2. We also report that BAHD1 modifies chromatin by changing histone methylation and acetylation, as well as DNA methylation, at a target gene, ESR1. These results allow us to propose that BAHD1 form, with MIER1, a scaffold assembling a new chromatin remodeling complex associated with HDAC1/2 : the BAHD1 complex. We then studied the role of BAHD1 in an organ targeted by Listeria, the brain. Our results indicate that a total deficiency in BAHD1 alters the overall transcriptome of this organ in mice. Most of the overexpressed genes are involved in nervous system functions, metabolism and neurological disorders. The predominantly downregulated genes are involved in innate immunity pathways, including interferon response genes. In addition, a haplodeficiency in Bahd1 causes behavioral problems. Compared to Bahd1+/+ mice, Bahd1+/- mice suffer from increased anxiety and changes in acoustic startle reflex. These results suggest that deregulation of BAHD1, through environmental or infectious stimuli, may have neuro-pathological effects.The second axis of my thesis focused on the study of InlP interactions with host nuclear proteins, identified by a double-hybrid screen. First, we show that InlP is an atypical internalin, with leucine-rich repeats characterized by an LPX2 motif. We then identify two nuclear proteins targeted by InlP: the splicing factor and tumor suppressor RBM5 and the corepressor RERE. When InlP is produced ectopically in human cells, it is localized in the nucleus, where it alters the formation of nuclear bodies enriched in RERE. In RBM5-overexpressing cells, InlP inhibits the pro-apoptotic effect of RBM5 and stimulates the formation of dense nuclear bodies associated with RBM5. These results suggest that InlP is a nucleomodulin acting on the assembly and disassembly of target protein storage compartments involved in the synthesis and splicing of host RNAs.This work opens perspectives in the understanding of host-pathogen interactions and in a better knowledge of patho-epigenetic mechanisms, as well as in cell biology and the understanding of membraneless nuclear organelles dynamics.

Campylobacteriosis is a leading foodborne illness worldwide, primarily caused by Campylobacter jejuni (C. jejuni) which is associated with poultry consumption. The emergence of antibiotic resistance has emphasized the need for alternative strategies to control C. jejuni colonization in poultry. To assess the prevalence of C. jejuni in poultry, 270 cloacal swab samples were collected from broilers raised under No-Antibiotics Ever system. Among these samples, 16.3% were identified as C. jejuni positive. Notably, these isolates exhibited a diverse range of virulence factors and antimicrobial resistance genes, with 61.36% of isolates showing hyper-motile and 20.45% demonstrating multidrug resistance. Following isolation, whole genome sequencing was conducted on four selected strains using a hybrid sequencing approach. Subsequently, the complete genomes of these C. jejuni strains were analyzed to identify vaccine candidates using reverse vaccinology. Three conserved potential vaccine candidates were identified as suitable targets for vaccine development, namely phospholipase A (PldA), TonB dependent transporter (ChuA), and cytolethal distending toxin (CdtB). Furthermore, the gene expression of these candidates was examined in four C. jejuni strains during host-pathogen interactions using avian macrophage cell line HD11. Significant upregulation of all three candidate genes were observed in the four tested C. jejuni strains during interaction with host cells, indicating their crucial role in C. jejuni infection. Additionally, the expression of immune genes was evaluated in avian macrophage cells to understand the immune responses during C. jejuni infection. The infection resulted in the upregulation of toll-like receptor genes (TLR-4), pro-inflammatory genes (IL-1β, IFN-γ, IL-6, IL-8L1), anti-inflammatory gene (IL-10), and iNOS2 gene expression. The observed immune response demonstrates the potential of C. jejuni to induce host immunity for protection. In conclusion, our study identifies three conserved potential vaccine candidates and provides insights into the immune responses induced by C. jejuni infection in avian macrophage cells. These findings are crucial for the development of an effective vaccine against C. jejuni, aiming to reduce C. jejuni transmission through poultry consumption and the risk of human infection.

Human coronavirus OC43 (HCoV-OC43) is a beta-coronavirus from the coronaviridae family. In contrast to SARS-CoV-2, HCoV-OC43 causes upper respiratory tract disease. However, because of their close phylogenic proximity but distinct pathologies, HCoV-OC43 is a very interesting surrogate to study and compare beta coronaviruses. As all viruses, the latter hijack cell machinery proteins to complete their life cycle. Cellular proteins, particularly those incorporated into virions are of particular interest since they often play a vital role in the virus life cycle. Our goal is to employ the proteomic pipeline we developed for HSV-1 to characterize the host proteins associated with highly purified extracellular HCoV-OC43 particles and finally expand it to SARS-CoV-2. To this end, high purity in sufficient yields is crucial as mass spectrometers pick up contaminants. The proteins present in cell culture medium serum, as well as the proteins carried by the exosomes produced by the cells or by the exosomes present in the cell culture media serum, are of particular concern. We utilized a series of methods to eliminate cell culture serum protein contaminations, enrich the viral particles, and separate exosomes from viral particles. For example, we have obtained an efficient separation of concentrated HCoV-OC43 virions from exosomes using density gradient fractionation. Mass spectrometry results on the purified fractions validated the enrichment of viral particles in the virus fraction and the lack of viral proteins in the mock samples. Most interestingly, we detected 69 host proteins unique to the virus fraction (compared to the mock), mostly regulating the RNA metabolism pathway followed by metabolite interconversion, protein modifying enzymes, and protein-binding activity modulator pathways. Since we also purified extracellular exosomes in the process, we probed whether the virus alters their protein content. Mass spectrometry revealed 51 unique proteins exclusively found in exosomes produced by HCoV-OC43 infected cells. These included translational proteins, metabolite interconversion enzymes, and scaffold proteins. Our preliminary RNA interference studies showed that knocking down 14 of these host proteins altered HCoV-OC43 titers. Studying host-virus protein interactions allows us to gain a deeper understanding of how viruses take advantage of host cells, and how we can develop novel viral therapeutics. / Le coronavirus humain OC43 (HCoV-OC43) est un bêta-coronavirus de la famille des coronaviridae. Contrairement au SRAS-CoV2, le HCoV-OC43 provoque une maladie des voies respiratoires supérieures. Cependant, en raison de leur proximité phylogénique étroite mais leur pathologie distincte, HCoV-OC43 est un substitut fort intéressant pour étudier et comparer les bêta-coronavirus. Comme tous les virus, ces derniers détournent les protéines de la machinerie cellulaire pour compléter leur cycle de vie. Les protéines cellulaires, en particulier celles incorporées dans les virions, sont particulièrement intéressantes puisqu'elles jouent souvent un rôle vital dans le cycle de vie du virus. Notre objectif est d'utiliser le pipeline protéomique que nous avons développé pour le HSV-1 afin de caractériser les protéines hôtes associées à des particules virales extracellulaires de HCoV-OC43 hautement purifiées et d'étendre cette approche au SRAS-CoV2. À cette fin, une pureté élevée avec des rendements suffisants est cruciale car les spectromètres de masse détectent les contaminants. Les protéines présentes dans le sérum du milieu de culture cellulaire, ainsi que les protéines portées par les exosomes produits par les cellules ou par les exosomes présentes dans le sérum du milieu de culture cellulaire, sont particulièrement concernées. Nous avons utilisé une série de méthodes pour éliminer les contaminations par les protéines sériques des cultures cellulaires, enrichir les particules virales et séparer les exosomes des virus. Nous avons ainsi obtenu une excellente séparation des virions HCoV-OC43 concentrés des exosomes en utilisant le fractionnement par gradient de densité. Les résultats de spectrométrie de masse sur les fractions purifiées ont validé l'enrichissement en particules virales dans la fraction virale et l'absence de protéines virales dans les échantillons contrôles. Plus intéressant encore, nous avons détecté 69 protéines hôtes uniques à la fraction virale (par rapport aux cellules non-infectées). Ces protéines sont principalement associées à la voie du métabolisme de l'ARN suivie de l'interconversion des métabolites, des enzymes modifiant les protéines et des voies modulatrices de l'activité de liaison aux protéines. Puisque nous avons séparés les exosomes des virus, nous en avons profiter pour évaluer si le virus altère leur contenu protéines. La spectrométrie de masse a de facto identifié 51 protéines uniques aux exosomes produits par les cellules infectées par HCoV-OC43. Celles-ci régulent des voies des protéines traductionnelles, des enzymes d'interconversion des métabolites et des voies des protéines d'échafaudage. Nos études préliminaires sur l’interférence ARN ont montré que l’inactivation de 14 de ces protéines hôtes modifiait le titre de HCoV-OC43. L'étude des interactions hôte-protéine virale nous permet de mieux comprendre comment les virus tirent parti des cellules hôtes et comment nous pouvons développer de nouvelles thérapies virales.

Le nicotinamide est une vitamine fournie par l'alimentation et utilisée en thérapie dans le traitement de certaines pathologies humaines. Chez Leishmania, un protozoaire parasite responsable des leishmanioses, cette vitamine présente une action toxique contre le parasite et une action synergique avec l'antimoine, la principale molécule utilisée dans le traitement des leishmanioses. En recherchant le mode d'action de cette vitamine, nous avons observé qu'elle était en réalité un précurseur essentiel à la synthèse du NAD+ chez le parasite, un cofacteur responsable de la plupart des réactions d'oxydoréduction chez tous les êtres vivants. Leishmania étant en effet dépourvu des voies de synthèse de novo du NAD+, il doit le générer à partir de précurseurs qu'il importe depuis son environnement (nicotinamide, nicotinamide riboside, acide nicotinique). Cette auxotrophie du parasite pour le NAD+ révèle donc un rôle ambivalent du nicotinamide, à la fois toxique à fortes concentrations et pourtant essentiel à sa survie en tant que précurseur majeur du NAD+. À partir des bases de données, nous avons reconstitué l'ensemble de la voie de synthèse du NAD+ chez Leishmania. Parmi les enzymes impliquées, nous avons identifié une nicotinamidase qui n'a pas d'homologue chez les mammifères, et qui assure la conversion du nicotinamide en acide nicotinique, première étape à la synthèse du NAD+. Cette enzyme étant un candidat intéressant pour le développement de molécules ciblant spécifiquement le parasite, nous avons réalisé la caractérisation fonctionnelle de ce gène. Son inactivation induit une diminution importante de la concentration en NAD+ chez le parasite et provoque un arrêt de la prolifération en culture, ainsi qu'une incapacité des mutants à établir une infection durable chez la souris. L'obtention de la structure de la nicotinamidase de L. infantum nous offre désormais la possibilité de développer des inhibiteurs spécifiques contre cette nouvelle cible thérapeutique. / Nicotinamide is a vitamin provided by food that is already used in human therapy. In Leishmania protozoan parasites, this molecule shows toxic activity against parasites and has synergistic activity with antimonials, the main drugs used to treat leishmaniasis. By investigating the mode of action of this cheap vitamin, we discovered that nicotinamide is in fact the main precursor of NAD+ synthesis in Leishmania, a redox cofactor essential for all living cells. Leishmania are indeed devoid of a de novo NAD+ pathway and must synthesize it by scavenging precursors from their environment (nicotinamide, nicotinic acid and nicotinamide riboside). This NAD+ auxotrophy reveals a mixed pattern of activity of nicotinamide in Leishmania, i.e. toxic at high concentrations but also essential for parasite survival through its role in NAD+ synthesis. All enzymes of the Leishmania NAD+ salvage pathway were then identified from genome databases. We focused on a putative nicotinamidase, which has no homolog in mammals and governs the conversion of nicotinamide to nicotinic acid, the first step in the NAD+ salvage pathway. Since this enzyme could be considered as an attractive therapeutic target to develop specific parasite inhibitors, we performed a functional analysis of the corresponding gene. Targeted deletion of the nicotinamidase encoding gene induced a marked drop in parasite NAD+ content and a phenotype with strongly delayed growth. Additionally, these mutants are unable to establish durable infections in mice. The crystal structure of the nicotinamidase from L. infantum will allow us to develop specific inhibitors against this new therapeutic target.

Ce travail a contribué à la compréhension des bases moléculaires de l'immunité de l'huître creuse par la caractérisation la diversité de trois effecteurs antimicrobiens de C. gigas et par l'appréhension du rôle de cette diversité dans les mécanismes de défense. Des analyses phylogénétiques de deux peptides antimicrobiens (AMPs), Cg-Défensines (Cg-Defs) et Cg-Proline rich peptide (Cg-Prp), et d'une protéine de type Bactericidal Permeability Increasing protein, Cg-BPI, nous a permis montrer la grande diversité pour les 2 AMPs, qui est générée par plusieurs mécanismes génétiques et par des pressions de sélection directionnelles, suggèrant une diversité fonctionnelle des variants. L'importance biologique de cette diversité a été étudiée pour trois variants de Cg-Defs. Une forte activité antimicrobienne a été mise en évidence contre les bactéries à Gram positive, mais celle-ci diffère selon les variants. De plus, nous avons démontré que le mécanisme d'action des Cg-Defs contre S. aureus repose sur l'inhibition de la biosynthèse du peptidoglycane par le piegeage de son précurseur, le lipide II. Finalement, l'expression des transcrits et la localisation de ces effecteurs en réponse à une infection par un Vibrio pathogène ont montré un réseau complexe des profils d'expression des différents antimicrobiens, au niveau des populations hémocytaires et des tissus d'huître, suggérant une interaction entre les antimicrobiens du fait de leur colocalization. La combinaison entre les familles ou entre les variants d'une même famille produit de fortes activités synergiques qui élargissent les spectres d'activité. Ainsi, la diversité produit par la coévolution entre hôte et pathogènes pourrait améliorer l'activité des AMPs d'huître, lui conférant une plus grande protection contre les pathogènes de son environnement. / This work contributed to the knowledge of the molecular bases of oyster immunity by the characterization of the diversity of three antimicrobials of C. gigas and the understanding of the role played by their diversity in the oyster antimicrobial response. Phylogenetic analyses of two antimicrobial peptides (AMPs), Cg-Defensins (Cg-Defs) and Cg-Proline rich peptide (Cg-Prp), and one Bactericidal Permeability Increasing protein, Cg-BPI, led us to the identification of a high diversity for both AMPs. Further analyses showed that this diversity is generated by gene duplication, allelic recombination and directional selection pressures, suggesting their functional diversification. The biological meaning of AMP diversity was investigated for the three major variants of Cg-Defs, which revealed a strong but variable potency against Gram-positive bacteria. We evidenced that oyster defensins kill S. aureus through binding to the cell wall precursor lipid II, resulting in the inhibition of peptidoglycan biosynthesis. Finally, transcript expression and localization of oyster antimicrobials after a pathogenic infection evidenced a complex network in their expression profiles in hemocyte populations and oyster tissues, suggesting a potential interplay between antimicrobials as a result of their colocalization. Indeed, the combination of oyster antimicrobials produced strong synergistic activities that enlarged their antimicrobial spectra. Thus, the diversity of oyster antimicrobials may provide significant means in acquiring functional divergence, probably concerned in the evolutionary arms race between hosts and their pathogens.From our data, it would provide oysters with a higher protection against the potential pathogens from their environment.

Mycobacterium tuberculosis (Mtb) is the pathogen causing tuberculosis (TB), a disease most often affecting the lung. 1.5 million people die annually due to TB, mainly in low-income countries. Usually considered a disease of the poor, also developed nations recently put TB back on their agenda, fueled by the HIV epidemic and the global emergence of drug-resistant Mtb strains. HIV-coinfection is a predisposing factor for TB, and infection with multi-drug resistant and extremely drug resistant strains significantly impedes and lengthens antibiotic treatment, and increases fatality. Mtb is transmitted from a sick individual via coughing, and resident macrophages are the first cells to encounter the bacterium upon inhalation. These cells phagocytose intruders and subject them to a range of destructive mechanisms, aiming at killing pathogens and protecting the host. Mtb, however, has evolved to cope with host pressures, and has developed mechanisms to submerge macrophage defenses. Among these, inhibition of phagosomal maturation and adaptation to the intracellular environment are important features. Mtb profoundly alters its phenotype inside host cells, characterized by altered metabolism and slower growth. These adaptations contribute to the ability of Mtb to remain dormant inside a host during latent TB infection, a state that can last for decades. According to recent estimates, one third of the world’s population is latently infected with Mtb, which represents a huge reservoir for active TB disease. Mtb is also intrinsically tolerant to many antibiotics, and adaptation to host pressures enhances tolerance to first-line TB drugs. Therefore, TB antibiotic therapy takes 6 to 9 months, and current treatment regimens involve a combination of several antibiotics. Patient noncompliance due to therapeutic side effects as well as insufficient penetration of drugs into TB lesions are reasons for treatment failure and can lead to the rise of drug-resistant populations. In view of the global spread of drug-resistant strains, new antibiotics and treatment strategies are urgently needed. In this thesis, we studied the interplay of the primary host cell of Mtb, human macrophages, and different Mtb phenotypes. A low-burden infection resulted in restriction of Mtb replication via phagolysosomal effectors and the maintenance of an inactive Mtb phenotype reminiscent of dormant bacteria. Macrophages remained viable for up to 14 days, and profiling of secreted cytokines mirrored a silent infection. On the contrary, higher bacterial numbers inside macrophages could not be controlled by phagolysosomal functions, and intracellular Mtb shifted their phenotype towards active replication. Although slowed mycobacterial replication is believed to render Mtb tolerant to antibiotics, we did not observe such an effect. Mtb-induced macrophage cell death is dependent on ESAT6, a small mycobacterial virulence factor involved in host cell necrosis and the spread of the pathogen. Although well-studied, the fate of ESAT6 inside infected macrophages has been enigmatic. Cultivation of Mtb is commonly carried out in broth containing detergent to avoid aggregation of bacilli due to their waxy cell wall. Altering cultivation conditions revealed the presence of a mycobacterial capsule, and ESAT6 situated on the mycobacterial surface. Infection of macrophages with this encapsulated Mtb phenotype resulted in rapid ESAT6-dependent host cell death, and ESAT6 staining was lost as bacilli were ingested by macrophages. These observations could reflect the earlier reported integration of ESAT6 into membranes followed by membrane rupture and host cell death. In conclusion, the work presented in this thesis shows that the phenotype of Mtb has a significant impact on the struggle between the pathogen and human macrophages. Taking the bacterial phenotype into account can lead to the development of drugs active against altered bacterial populations that are not targeted by conventional antibiotics. Furthermore, deeper knowledge on Mtb virulence factors can inform the development of virulence blockers, a new class of antibiotics with great therapeutic potential.

A leishmaniose é um termo global para doenças causadas por parasitos do gênero Leishmania, sendo a Leishmaniose Visceral (LV) a forma mais grave da doença. No Brasil é causada pelo parasita Leishmania (Leishmania) infantum chagasi. Para garantir a sua sobrevivência, alguns parasitas são capazes de manipular respostas de defesa das células do sistema imune. Recentes estudos demonstraram a participação da proteína imunomodulatória CD200 durante o processo de infecção de L. (L.) amazonenses. O presente estudo teve como objetivo investigar se os parasitos L. (L.) infantum chagasi são capazes de induzir a expressão da proteína CD200 durante o processo infeccioso. Em ensaios de infecção ex vivo, não foi observado proliferação de parasitas intracelulares. Apesar disso, L. (L.) infantum chagasi foi capaz de induzir a expressão do gene CD200. De maneira interessante, diferente de infecções por L. (L.) amazonenses, a indução de CD200 nessas células foi observada em tempos mais tardios de infecção. Ensaios de imunoprecipitação e Western blot indicaram a síntese da proteína, que atingiu os seus maiores níveis a 120 horas pós-infecção. A presença de CD200 sugere o envolvimento dessa molécula em tempos mais tardios de infecção por L. (L.) infantum chagasi. / Leishmaniasis is a global term for diseases caused by parasites of the genus Leishmania, and Visceral Leishmaniasis (VL) are the most severe form of the disease. In Brazil is caused by the parasite Leishmania (Leishmania) infantum chagasi. To ensure their survival, some parasites can handle defensive responses of the cells of the immune system. Recent studies have demonstrated the participation of immunomodulatory protein CD200 during the infection process of L. (L.) amazonenses. This study aimed to investigate whether the parasites L. (L.) infantum chagasi are capable of inducing the expression of CD200 protein during the infectious process. In trials of ex vivo infection, there was no proliferation of intracellular parasites. Nevertheless, L. (L.) infantum chagasi was able to induce the expression of CD200 gene. Interestingly, unlike infection by L. (L.) amazonenses, CD200 induction of these cells was observed at later times in infection. Immunoprecipitation assays and Western blot indicated protein synthesis, which reached their highest levels at 120 hours post-infection. The presence of CD200 suggests the involvement of this molecule at later times of infection with L. (L.) infantum chagasi.

A murcha bacteriana, causada por Ralstonia solanacearum, afeta principalmente as solanáceas, destacando-se as culturas da batata, berinjela, jiló, pimentão e tomate. No presente trabalho foi conduzida a caracterização molecular de isolados de R. solanacearum e sua possível relação com características relacionadas à morfologia, bioquímica, patogenicidade, agressividade e distribuição geográfica. Foram utilizados 51 isolados pertencentes à biovar 2, sendo 9 provenientes de berinjela e 42 de batata, coletados em diversas regiões brasileiras. A análise molecular permitiu separar os isolados em quatro grupos distintos de padrões de bandas para os iniciadores BOX e ERIC, e em cinco para o iniciador REP. Não foi encontrada relação dos grupos de isolados caracterizados molecularmente com tamanho de colônias, ocorrência de mutantes, produção de melanina, capacidade de colonização do sistema radicular e resistência a antibióticos/fungicidas. A identificação de isolados de batata, como biovar 2-A, e de berinjela, como biovar 2-T, com base em teste bioquímico do uso de trealose, foi confirmadas pela análise molecular. Não houve variação de agressividade entre os isolados inoculados em batata e berinjela, exceção feita ao isolado avirulento CNPH-65. Portanto, isolados das biovares 2-A e 2-T podem infectar estas duas hospedeiras com a mesma intensidade sob altas temperaturas. Para todos os isolados, o desenvolvimento da população bacteriana foi significativamente maior no sistema radicular de plantas das cultivares suscetíveis, tanto para batata como para berinjela. No entanto, dentro de cada cultivar, os isolados se comportaram de maneira semelhante, não sendo possível fazer distinção entre os mesmos. A tentativa de se associar grupos de isolados caracterizados molecularmente com os locais de origem revelou alguns aspectos interessantes. O grupo I agregou somente isolados do Paraná. No grupo II ficaram isolados da Bahia, Distrito Federal e do Paraná. No Grupo III, foram reunidos todos os isolados de berinjela e um único de batata, sendo todos procedentes do Distrito Federal. O grupo IV, de forma semelhante ao grupo II, reuniu isolados de locais diversos como Paraná, Goiás, Rio Grande do Sul e Distrito Federal. Portanto, nos grupos I e III parece haver uma tendência de relação entre grupamento molecular e local de origem, enquanto que para os grupos II e IV, isolados de características genéticas similares são provenientes de locais distintos, apontando considerável diversidade genética do patógeno. / The bacterial wilt disease caused by Ralstonia solonacearum affects mainly the solanaceous species, specially potato, eggplant, peppers, tomato and brazilian gilo (Solanum gilo). This work reports the molecular characterization of R. solanacearum biovar 2 isolates and the possible relationship of this molecular data with other characteristics related to morphology, biochemistry, pathogenicity, aggressiveness and geographical distribution. Fifty-one biovar 2 isolates were studied, 9 isolated from eggplant and 42 from potato, all of them collected from different regions of Brazil. According to the molecular analysis, the isolates were clustered in four different groups, with distinct band patterns to the primers BOX and ERIC, and five groups to the primers REP. There was no relationship between the groups clustered through molecular analyses and phenotypic characteristics, such as colony size, presence of mutants, melanin presence, capability of root system colonization and antibiotic/fungicide resistance. The identification of potato isolates as the biovar 2-A, and the eggplant isolates as biovar 2-T, based on biochemical tests using trealose were confirmed with the molecular analyses. There was no variation of aggressiveness in the isolates inoculated on potato an eggplant, except the avirulent isolate CNPH-65. Consequently, isolates of biovars 2-A and 2-T are able to infect both hosts with the same aggressiveness under high temperatures. The population of all isolates developed in significant levels at the root system of susceptible cultivars of both hosts, potato and eggplant. However, considering each cultivar tested, there was no difference between isolates. Interesting results were observed when the isolates clustered based on molecular data were associated with the geographical region of their collection. The group I clustered only the isolates collected in Paraná. The group II clustered the isolates collected in Bahia, Federal District and some in Paraná. The group III clustered all isolates from eggplant and only one of potato, all of them collected in the Federal District. The group IV, as the group II, clustered isolates from different regions, like Paraná, Goiás, Rio Grande do Sul and Federal District. These results suggest a relationship between the isolates clustered through molecular analysis in the groups II and III and their geographical region of collection. The isolates clustered in the same way, with similar genetic background in the groups II and IV, were however collected in different regions, showing the great genetic variation of this pathogen.