Tableau d'honneur de la Faculté des études supérieures et postdorales, 2015-2016 / Plusieurs protozoaires se nourrissant de bactéries peuvent sécréter des corps multilamellaires (CML) dans lesquels se retrouvent certaines bactéries pathogènes ayant résisté à la digestion par la cellule hôte. Ces bactéries enrobées dans des CML bénéficient de protections supplémentaires contre divers stress et sont susceptibles d’être aérosolisées et inhalées par l’humain. La présente étude visait à élucider le rôle physiologique des CML et les mécanismes de leur formation chez l’amibe modèle Dictyostelium discoideum. L’analyse en spectrométrie de masse du contenu protéique des CML a révélé la présence de quatre protéines majeures, incluant SctA communément associée aux pycnosomes. La fonction biologique des CML reste inconnue, mais il a été déterminé que les amibes et autres protozoaires pouvaient réinternaliser les CML sécrétés. Ces résultats permettent d’orienter les recherches afin d’élucider le véritable rôle des CML et ainsi mieux comprendre leur implication dans la transmission de bactéries pathogènes d’origine environnementale. / Many protozoa that feed on bacteria secrete multilamellar bodies (MLBs). MLBs have been found to harbour pathogenic bacteria that are resistant to degradation by the host cell. MLBs serve to protect these bacteria from various external stresses and could be aerosolized and subsequently inhaled by humans. The aim of this study was to elucidate the physiological role of MLBs and the mechanisms governing their formation in the model amoeba Dictyostelium discoideum. Mass spectrometric analyses of purified MLBs revealed the presence of four major proteins, including SctA, a protein generally associated with pycnosomes. The biological function of MLBs remains unclear, but we demonstrated that the amoeba and another protozoan can reinternalize secreted MLBs. These results provide new insight into the role of MLBs in the cell and deepen our understanding of the involvement of MLBs in the transmission of environmental pathogenic bacteria.

Titre de l'écran-titre (visionné le 2 mai 2023) / Dictyostelium discoideum est un protozoaire largement utilisé comme organisme modèle. Cette amibe se nourrit majoritairement via la phagocytose de bactéries, qui sont digérées dans la voie phago-endocytique. Lorsque nourrie avec des bactéries digestibles, D. discoideum produit des corps fécaux composés de membranes lipidiques concentriques appelés corps multilamellaires (CML). Le rôle exact des CML ainsi que les mécanismes régissant leur production sont encore peu connus. Dans l'optique d'approfondir les connaissances sur les CML et sur le fonctionnement de la voie phago-endocytique en général, la souche mutante de D. discoideum tstD- a été caractérisée. Ce mutant ne possède pas de protéine TSPOON fonctionnelle, une protéine faisant partie du complexe TSET. Chez D. discoideum, le complexe protéique TSET est impliqué dans le transport vésiculaire et dans le renouvellement de la membrane plasmique. Le mutant tstD- semble avoir une morphologie cellulaire et des CML semblables à ceux de sa souche parentale Ax2. De plus, l'osmorégulation, la cytokinèse ainsi que la capacité de prédation ne semblent pas altérées chez le mutant tstD-. Cependant, le mutant tstD- produit des plages de phagocytose différentes de celles d'Ax2 sur des souches d'Aeromonas salmonicida qui ne possèdent pas de système de sécrétion de type trois (SSTT). Au niveau de l'organisation de la voie phago-endocytique, elle semble similaire pour le mutant tstD- et Ax2 de manière générale, mais la détection de la protéine p25 semble affectée en fonction du produit utilisé pour la perméabilisation des cellules et de la souche parentale testée. Cette étude a permis d'en apprendre davantage sur les moyens employés pour étudier les CML chez D. discoideum et ouvre aussi la porte à une meilleure compréhension du fonctionnement de la voie-phago-endocytique et des outils utilisés pour la caractériser à travers l'étude du mutant tstD-. / Dictyostelium discoideum is a protozoan widely used as a model organism. This amoeba feeds mainly through phagocytosis of bacteria, which are digested in the phago-endocytic pathway. When fed with digestible bacteria, D. discoideum produces faecal pellets composed of concentric lipid membranes called multilamellar bodies (MLBs). The exact role of MLBs and the mechanisms governing their production are still poorly understood. In order to deepen the knowledge on MLBs and on the functioning of the phago-endocytic pathway in general, the mutant strain of D. discoideum tstD- was characterized. This mutant lacks a functional TSPOON protein, a protein that is part of the TSET protein complex. In D. discoideum, the protein complex TSET is involved in vesicular transport and in plasma membrane turnover. The mutant tstD- appears to have similar cell morphology and MLBs to its parental strain Ax2. In addition, osmoregulation, cytokinesis, and predation capacity do not seem to be altered in the tstD- mutant. However, tstD- produces different phagocytosis plaques than Ax2 on strains of Aeromonas salmonicida that lack a type three secretion system. Regarding the organization of the phago-endocytic pathway, it seems generally similar in both tstD- and Ax2, but the detection of the p25 protein seems affected depending on the product used for cell permeabilization and the parental strain tested. This study has made it possible to learn more about the means used to study MLBs in D. discoideum and opens the door to a better understanding of the functioning of the phago-endocytic pathway as well as the tools available to characterize it through the study of the mutant tstD-.

Tesis entregada a la Universidad de Chile en cumplimiento parcial de los requisitos para optar al grado de Doctor en Ciencias con Mención Microbiología. / Salmonella Typhimurium is an enteric pathogen able to infect different animal hosts, including humans. In immunocompetent humans, S. Typhimurium mainly causes gastroenteritis, a disease characterized by an inflammatory diarrhoea with massive neutrophil infiltration in the ileum and colon. The infective cycle of Salmonella starts with the ingestion of bacteria that reach the small intestine and invade epithelial cells by its apical face. After crossing the epithelial barrier, bacteria are captured by phagocytic cells of the immune system present in the sub-epithelium, such as macrophages, neutrophils and dendritic cells, being contained within a membrane bound compartment. Here, Salmonella subverts the endocytic route, avoiding the fusion of this compartment with the lysosomes and generating the Salmonella-containing vacuole (SCV). In this compartment, Salmonella is able to survive and replicate. The ability to modify this intracellular niche explains the ability of this pathogen to survive intracellularly. To carry out this process, Salmonella employs two Type Three Secretion Systems (T3SS) and an arsenal of secreted effector proteins in order to take control over the eukaryotic cell. An important aspect of Salmonella’s life cycle that has not been studied in detail is its survival in the environment, where bacteria are exposed to predation by protozoa, and specially by amoebae. These organisms are specialized phagocytes that feed on bacteria and fungi. To address this interaction, we and other groups use amoeba models to characterise the molecular processes involved in the survival of intracellular pathogens within environmental protozoa. Among these model organisms, the social amoeba Dictyostelium discoideum is amenable for molecular analyses in laboratory settings and several tools have been developed in this organism for the study of different aspects of its interaction with bacterial pathogens. Recently, our group described that S. Typhimurium is able to survive intracellularly in the social amoeba Dictyostelium discoideum, and that mutants in genes required for virulence in other infection models present survival defects in this host. Despite of this, the mechanisms that allow the intracellular survival of this pathogen in this kind of organism have not been studied in detail. This Thesis proposed the characterization at the cellular level of this interaction, with a focus on two secreted effector proteins of S. Typhimurium that are directly related to SCV generation and modification in other cell models: SopB and SifA. Our results show that these effectors are needed for intracellular survival of S. Typhimurium in D. discoideum. Furthermore, by means of a combination of microscopy and proteomic analyses we were able to characterise the protein composition of the vacuolar compartment containing Salmonella in this host. Our results show that known markers linked to this compartment in other cell types and the autophagy machinery play a role in the biogenesis of this intracellular niche in D. discoideum. / Salmonella Typhimurium es un patogeno enterico que tiene la capacidad de infectar diversos hospederos animals, incluyendo el ser humano. En individuos inmunocompetentes, S. Typhimurium provoca gastroenteriris, una enfermedad diarreica inflamatoria caracterizada por la masiva infiltracion de neutrofilos en el ileon y el colon. El ciclo infectivo de Salmonella comienza con la ingestion de las bacterias que al llegar al intestino delgado invaden las celulas epiteliales por la cara apical. Luego de cruzar la barrera epitelial, las bacterias son capturadas por las celulas fagociticas del sistema inmune que residen en el sub-epitelio, como macrofagos, neutrofilos y celulas dendriticas, quedando contenida en un compartimento membranoso. En esta etapa, Salmonella interviene la ruta endocitica, evitando la fusion de este compartimento con el lisosoma y generando la vacuola contenedora de Salmonella (Salmonella-containing vacuole: SCV). En este compartimento, Salmonella es capaz de sobrevivir y replicarse. La habilidad de modificar este nicho intracelular explica la habilidad de este patogeno de sobrevivir intracelularmente. Para esto, Salmonella utiliza dos Sistemas de Secrecion Tipo Tres (Type Three Secretion Systems: T3SS) y un arsenal de proteinas efectoras secretadas para tomar control sobre la celula eucarionte. Por otra parte, un importante aspecto del ciclo de vida de Salmonella que no ha sido estudiado en detalle es su supervivencia en el ambiente, donde las bacterias se encuentran expuestas a la depredacion por protozoos y en particular, amebas. Estos organismos son fagocitos profesionales que se alimentan de bacteria y hongos. Recientemente, nuestro grupo describio que S. Typhimurium es capaz de sobrevivir intracelularmente en la ameba social Dictyostelium discoideum y que mutantes en genes requeridos para la virulencia en numerosos modelos de infeccion tambien presentan defectos de supervivencia en este hospedero. A pesar de esto, los mecanismos que le permiten a este patogeno en este tipo de organismo no han sido estudiado en detalle. Para entender esta interaccion, nosotros y otros grupos usamos modelos de ameba a fin de caracterizar los procesos moleculares involucrados en la supervivencia de patogenos intracelulares en el interior de protozoos ambientales. Dentro de estos organismos modelo, la ameba social Dictyostelium discoideum es sencilla para el analisis molecular en condiciones de laboratorio. Por otra parte, numerosas herramientas se han desarrollado en este organismo para el estudio de diversos aspectos de su interaccion con patogenos bacterianos. Esta Tesis propuso caracterizar a nivel cellular esta interaccion, enfocandonos en dos proteinas efectoras secretadas de S. Typhimurium que estan directamente relacionadas a la formacion y modificacion de la SCV en otros modelos celulares: SopB y SifA. Nuestros resultados muestran que estos efectores son necesarios para que S. Typhimurium sobreviva intracelularmente en D. discoideum. Adicionalmente, mediante una combinacion de tecnicas de microscopia y analisis proteomicos pudimos caracterizar la composicion proteica de este compartimento vacuolar que contiene a Salmonella en este hospedero. Nuestros resultados muestran que marcadores asociados a la SCV en otras lineas celulares se encuentran en elcompartimento que se genera en D. discoideum y que la maquinaria de autofagia juega un rol importante en la biogenesis de este nicho intracelular en D. discoideum. / FONDECYT grants 1140754 y 1171844, CONICYT Doctoral Fellowship 21140615. / Enero 2020.

Bei der Gattung Legionella handelt es sich um aquatische Stäbchenbakterien, die sich intrazellulär in verschiedenen Protozoen vermehren können. Neben der Nutzung des Protozoenwirtes können humanpathogene Legionella-Spezies in den Alveolarmakrophagen des menschlichen Respirationstraktes replizieren. Diese Besiedelung der Lunge kann zu einer atypischen Pneumonie, der Legionärskrankheit, führen. Humanpathogene Vertreter der Gattung Legionella weisen somit ein duales Wirtssystem auf. Die Wirtsspezifität phylogenetisch verschiedener Legionella Spezies wurde bislang nicht systematisch analysiert. Mit Hilfe von Infektionsversuchen konnte in dieser Arbeit gezeigt werden, dass für unterschiedlichste Legionella Spezies Acanthamoeba castellanii ein gut geeigneter Wirt darstellt. Hartmannella vermiformis und Naegleria gruberi ermöglichen dagegen nur einem eingeschränkten Legionella-Spektrum ein intrazelluläres Wachstum. Die jeweils höchsten Vermehrungsraten zeigten dabei in allen Amöben die Umweltisolate LLAP 10 und L. lytica sowie der humanpathogene Stamm L. pneumophila Corby. Außerdem scheint die Virulenz humanpathogener Legionellen-Spezies korreliert zu sein mit der Nutzung eines breiten Wirtsspektrums. Ciliaten wie Tetrahymena pyriformis sind im Gegensatz zu den Amöben als Wirte nicht so gut geeignet. Im Vergleich zu den Amöben ist sowohl die Anzahl der sich intrazellulär in T. pyriformis replizierenden Legionella-Spezies sowie deren Replikationsrate erniedrigt. Ein Schwerpunkt dieser Arbeit war es Dictyostelium discoideum als neues Wirtsmodell zu etablieren. Bei dieser gut erforschten Bodenamöbe stehen zahlreiche molekularbiologische Methoden für das Manipulieren des Genoms zur Verfügung. Somit ist es möglich, die während einer Infektion benötigten Wirtsfaktoren von Seiten der Amöbe näher zu untersuchen. Mittels Infektionsversuchen sowie fluoreszenz- und elektronenmikroskopischer Methoden konnte die intrazelluläre Replikation von LLAP 10, L. lytica und L. pneumophila in D. discoideum gezeigt werden. Für L. pneumophila konnte durch FACS-Analyse festgestellt werden, dass Bakterien dieser Legionella-Spezies genauso wie in den bisher untersuchten Wirtszellesystemen zu Beginn der Infektion in einem nicht angesäuerten Kompartiment vorliegen. Für alle weiteren verwendeten Legionella Spezies sowie hitzeabgetötete L. pneumophila und die Futterbakterien Klebsiella aerogenes konnte dagegen eine Ansäuerung des Phagosoms nachgewiesen werden. Kolokalisierungsstudien des lysosomalen Markers DdLIMP mit Legionellen bestätigte außerdem eine Inhibierung der Phagolysosomfusion bei L. pneumophila, nicht jedoch bei der sich nicht replizierenden Spezies L. hackeliae. Die Untersuchung einer spezifischen Profilin-minus Dictyostelium-Mutante offenbarte eine erhöhte Phagozytoserate von Legionellen durch die Wirtszellen. Daraus resultierte auch eine leicht gesteigerte intrazelluläre Vermehrungsrate dieser Bakterien. Profilin ist ein Aktin-bindendes Protein und an der Regulation von Aufnahmeprozessen beteiligt. Weiterhin wurde in dieser Arbeit eine Methode zur Isolierung Bakterien-haltiger Phagosomen aus D. discoideum etabliert. Die magnetische Reinigung von Phagosomen über paramagnetische, Bakterien-konjugierte Beads erwies sich als nicht praktikabel. Die daraufhin entwickelte Anreicherung der Phagosomen über Dichtegradienten-Zentrifugation erforderte jedoch zusätzlich die Eliminierung kontaminierender Lysosomen und Mitochondrien. Die Analyse des phagosomalen Proteoms erfolgte mittels Messung von Enzymaktivitäten und Western-Blotting-Experimenten. Dabei konnten keine quantitativen Unterschiede typischer lysosomaler Marker zwischen gereiften und ungereiften Phagosomen mit lebenden bzw. toten L. pneumophila detektiert werden. Ebenso verlief der Vergleich von ungereiften LLAP 10-haltigen Phagosomen und gereiften Klebsiella-haltigen Phagosomen. Dagegen zeigte die 2D-Gelelektrophorese des phagosomalen Proteoms vier Proteine, die in Phagosomen mit toten L. pneumophila Corby stärker exprimiert waren als in Phagosomen mit lebenden Legionellen. Weiterhin wurde ein Protein detektiert, das für Phagosomen, die lebende L. pneumophila Bakterien beinhalten, spezifisch ist. Dabei könnte es sich um einen von L. pneumophila zur Replikationsvakuole rekrutierten Wirtsfaktor handeln. / Legionella pneumophila is the causative agent of Legionnaires’ disease. It is able to replicate in cells of the respiratory tract namely the alveolar macrophages. In the environment, L. pneumophila, like other Legionellae lives in fresh water habitats and replicates intracellularly in protozoa. Therefore the pathogenic species of the genus Legionella possess a dual host system. Until now, very little is known about the host specificity of phylogenetically different Legionella species. This work revealed that the amoeba Acanthamoeba castellanii can serve as a host for most of the Legionella species tested. In contrast, in Hartmannella vermiformis and Naegleria gruberi only a reduced number of different Legionella species are able to replicate intracellularly. In all three amoeba species the environmental isolates LLAP 10 and L. lytica, as well as the pathogenic L. pneumophila, showed the highest replication rate among the Legionella species tested. In the ciliate T. pyriformis, the number of replicating Legionella species and the replication rate are diminished. Therefore amoebae are more suitable than ciliates as a host for Legionella infections. A major aim of this work was to establish Dictyostelium discoideum as a new host model system. This soil amoeba is genetically well studied. Furthermore, there are several different methods for the manipulation of the genome. Therefore it is possible to examine the host-pathogen interaction from the perspective of the host. The intracellular replication of LLAP 10, L. lytica and L. pneumophila in D. discoideum has been shown by determination of CFU-values in infection assays, as well as by fluorescent and electron microscopy methods. For L. pneumophila, it could be shown with FACS-analysis that the bacteria live in a phagosome with an almost neutral pH. This corresponds to the observed results in phagosomes in human macrophages and amoebae. All other Legionella species, as well as the food bacterium Klebsiella aerogenes, and heat killed L. pneumophila, are found in an acidic vesicle. Moreover, phagolysosom fusion was inhibited by L. pneumophila as demonstrated by co-localization studies with the lysosomal marker DdLIMP. No co-localization could be shown with L. pneumophila, while non replicating Legionellae clearly indicated that DdLIMP was integrated in the phagosomal membrane. Using a specific profilin minus mutant of Dictyostelium it could be shown by FACS-analysis that the uptake of Legionellae in these mutant cells occurs with a higher phagocytosis rate. Furthermore, the intracellular replication rate of Legionella bacteria is slightly increased. Profilin is an actin binding protein which is involved in regulation uptake processes. A method for isolating bacteria containing phagosomes from Dictyostelium was also established. Because it was not possible to isolate bacteria labeled bead phagosomes magnetically, a density gradient centrifugation was used. Contaminating lysosmes were eliminated by loading these organelles with iron particles and the use of an electromagnet. Contaminating mitochondria were eliminated by “heavy labeling” the organelles with a substrate for the succinat dehydrogenase and thereby increasing the specific density. Analysis of the phagosomal proteom occurred by measuring enzyme activities and western blotting experiments. No differences in the amount of lysosomal markers could be detected between phagosomes harboring living or dead L. pneumophila and phagosomes harboring LLAP 10 or K. aerogenes, respectively. In contrast, 2D gel electrophoresis revealed four proteins expressed in a greater amount in phagosomes containing dead L. pneumophila, and one protein specific for proteins harboring living L. pneumophila. This protein could be a host factor which is recruited to the phagosome by L. pneumophila

No description available.

Thesis (M. Sc)--York University, 2000. Graduate Programme in Biology. / Typescript. Includes bibliographical references (leaves 87-100). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://wwwlib.umi.com/cr/yorku/fullcit?pMQ59208.

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The Aurora kinases are highly conserved serine/threonine kinases that play essential roles throughout mitosis. In metazoans, these functions are mediated by Aurora A and B at the spindle poles and the equatorial region respectively. I show here that Dictyostelium contains a single Aurora kinase, DdAurora that displays characteristics of both Aurora A and B. Like Aurora A, DdAurora has an extended N-terminal domain with an A-box and localizes to the spindle poles during early mitosis. Like Aurora B, DdAurora localizes to centromeres in metaphase, the central spindle during anaphase and the cleavage furrow at the end of cytokinesis. In addition to these known features of Aurora A and B, I found that DdAurora remains associated with centromeres during anaphase and telophase which has not been shown in any other organisms. INCENP is known to be an important binding partner of Aurora B. In Dictyostelium the conserved C-terminal IN-box domain of DdINCENP is essential for its interaction with DdAurora and for the localization of DdAurora to the central spindle. In contrast, the centromeric and spindle pole localization of DdAurora does not require an interaction with DdINCENP. Surprisingly, a truncated DdINCENP protein lacking the IN-box domain can still localize on centromeres and the central spindle even though it does not bind to DdAurora. I also found that the localization of DdAurora to the central spindle requires Kif12, a protein similar to mitotic kinesin like protein 2 (MKLP2). However, this requirement is suppressed by the overexpression of GFP-DdINCENP. GFP-DdINCENP can localize to the central spindle in the absence of Kif12 and it probably recruits DdAurora to the same location through their strong interaction. Finally, I demonstrated that Myosin II heavy chain is important for the proper localization of the DdAurora/DdINCENP complex to the cleavage furrow during late cytokinesis. With the exception of DdINCENP, no other binding partner or substrate of DdAurora has been identified in Dictyostelium. By performing large-scale immunoprecipitation in wild-type cells, I identified several potential binding partners/substrates of DdAurora, including topoisomerase B and HspA. Future esearch on these proteins may help to elucidate DdAurora function in different stages of M phase.

During development, Dictyostelium discoideum cells assume muticellularity via their collective aggregation. Cell-cell adhesion is required for morphogenesis, cell differentiation, cell sorting and gene expression during development. TgrC1 is a heterophilic cell adhesion molecule which is indispendable for complete development. TgrC1 can be considered as the most important cell adhesion molecule for D. discoideum development because deletion of the tgrC1 gene completely arrests development at the loose aggregate stage and inhibits fruiting body formation. In order to investigate the biological role of TgrC1 during development, I have chosen to identify and charactize the extracellular heterophilic partner and the cytoplasmic binding partner(s) of TgrC1. Using different biochemical approaches, we identified TgrB1 as the heterophilic binding partner of TgrC1 and demonstrated that their association is mediated through IPT/TIG domains in the extracellular region of both proteins. Both tgrB1 and tgrC1 share the same transcriptional promoter and their spatiotemporal expression pattern is identical during development. We also examined the assembly of TgrC1-TgrB1 complexes via the split green fluorescence protein complementation assay and the fluorescence resonance energy transfer approach. Whereas TgrC1 is capable of forming cis-homodimers spontaneously, cis-homodimerization of TgrB1 depends on its trans-interaction with TgrC1. A model of the assembly process has been proposed. To investigate signalling events initiated by the interaction between TgrB1 and TgrC1, pull-down assays were employed and led to the identification of myosin heavy chain kinase C as the cytoplamic partner of TgrC1. Mutational analysis showed that the basic residues in the short cytoplasmic domain of TgrC1 are critical to the binding with MHCK-C. Disruption of the interation between MHCK-C and TgrC1 results in an alteration of cell motility at the aggregation stage and aberrant cell sorting in slugs. These studies have highlighted the role of TgrB1-TgrC1 complexes in the regulation of morphogenesis during Dictyostelium development.

The slime mould Dictyostelium discoideum contains a novel cAMP-binding protein, CABPl, that is composed of two subunits. Anti-CABPl monoclonal antibodies were used to isolate a cDNA from a $ lambda$gtll expression library. In hybrid selection experiments, this cDNA was found to be complementary to mRNAs encoding both CABPl subunits and also to share some homology with two polypeptides, p34 and p31, that copurify with CABPl. Further analysis showed that the two CABPl polypeptides are identical except for an additional 37 amino acids present in the larger polypeptide. Both polypeptides are encoded by a single gene and the production of the two CABPl mRNAs is accomplished by an unusual splicing event. The p34 and p31 polypeptides are smaller but highly homologous to the two CABPl polypeptides and are probably produced in a similar fashion. The carboxyl halves of the four polypeptides show a 50% similarity to two polypeptides of a tellurium anion resistance determinant encoded on a bacterial plasmid.