Vibrio tapetis est une bactérie pathogène responsable de la Maladie de l'Anneau Brun(MAB) chez la palourde japonaise Ruditapes philippinarum. Cette vibriose est induite par l'adhésion du pathogène à la lame périostracale provoquant ainsi une décalcification de la coquille du bivalve. Nous nous sommes intéressés à un aspect de la pathogénicité de V tapetis encore jamais exploré jusqu'à présent : la formation de biofilm. Chez de nombreuses espèces bactériennes, la pathogénicité est étroitement liée à ce comportement microbien particulier qu'est le biofilm. Au cours de cette étude, nous avons ainsi caractérisé pour la première fois le biofilm de la souche V tapetis CECT4600. La composition de la matrice du biofilm a également été examinée. Différents types de microscopies ont été utilisés pour observer le biofilm de V tapetis, nous permettant de mettre en évidence à la surface du biofilm la présence de composants sphériques de nature inconnue. Ces composants ont été retrouvés dans les biofilms de différentes souches de V tapetis et une analyse ultra-structurelle indique qu'il pourrait y avoir un lien physique entre ces composants et les bactéries. Ces composants particuliers du biofilm de V tapetis présentent une taille et un aspect de surface différents de ceux de la bactérie et semblent également contenir de l'ADN et des protéines. L'étude de l'effet de paramètres ayant un effet sur la prévalence de MAB a été réalisée et a permis notamment de mettre en évidence la capacité de V tapetis à persister et à développer des biofilms dans ces conditions jugées défavorables à l'établissement de la maladie. L'étude expérimentale de gènes potentiellement impliqués dans des fonctions liées à la formation de biofilm a été menée par la construction d'un mutant de V tapetis. La délétion d'un gène du quorum sensing (cqsA) a été réalisée et la formation de biofilm par ce mutant a également été examinée, révélant un effet exacerbé sur le biovolume du biofilm à 24h de culture. Enfin, l'activité anti- biofilm du surnageant de culture d'une bactérie marine, Pseudoalteromonas sp. 3J6, sur le biofilm de V tapetis a été testée, révélant une inhibition de l'adhésion bactérienne et de la formation du biofilm. Le traitement d'un biofilm préformé par ce surnageant s'est révélé également très efficace, manifestant ainsi le potentiel de cette bactérie et son surnageant pour la lutte « anti-Vibrio » en aquaculture. / Vibrio tapetis is a pathogenic bacterium causing the Brown Ring Disease (BRD) in Manilaclam Ruditapes philippinarum. This vibriosis is induced by bacterial adhesion on the periostracal lamina, yielding a decalcification of bivalve shell. We focused on one aspect of V tapetis pathogenicity never explored so far: biofilm formation. As in many bacterial species, pathogenesis is likely related to this microbial behavior that is the biofilm. In this study, V tapetis biofilm was characterized for the first time. The composition of the biofilm matrix was also examined. Different microcopy techniques were used to observe V tapetis biofilm, allowing us to highlight at the top of the biofilm the presence of spherical components. These peculiar components were found in biofilms of different V tapetis strains and an ultra- structure analysis indicates that there may be a physical link between these components and bacterial cells. The spherical components of V tapetis biofilm display a size and a different surface aspect than bacteria ones. Moreover, they seem to contain DNA and proteins. We also examined the effect of parameters that affect BRD prevalence and we highlighted the ability of V tapetis to persist and form biofilms in these unfavorable conditions for the disease development. Experimental study of genes potentially involved in functions related to biofilm formation was carried out by construction of a V tapetis mutant. The deletion of a quorum sensing gene (cqsA) was performed and subsequent biofilm formation was examined, revealing an exacerbated effect on the biovolume of a 24h biofilm. Finally, the antibiofilm activity of the culture supernatant of a marine bacterium, Pseudoalteromonas sp. 3}6, against V tapetis biofilm was tested, revealing the inhibition of bacterial attachment and biofilm formation. Treatment of a preformed biofilm by this supernatant also very efficient, highlighting the potential of this bacterium and its supernatant in the "anti-Vibrio" fight inaquaculture.

The Hubble Space Telescope Wide Field Camera 3 (WFC3) near-IR channel is extensively used in time-resolved observations, especially for transiting exoplanet spectroscopy as well as. brown dwarf and directly imaged exoplanet rotational phase mapping. The ramp effect is the dominant source of systematics in the WFC3 for time-resolved observations, which limits its photometric precision. Current mitigation strategies are based on empirical fits and require additional orbits to help the telescope reach a thermal equilibrium. We show that the ramp-effect profiles can be explained and corrected with high fidelity using charge trapping theories. We also present a model for this process that can be used to predict and to correct charge trap systematics. Our model is based on a very small number of parameters that are intrinsic to the detector. We find that these parameters are very stable between the different data sets, and we provide best-fit values. Our model is tested with more than 120 orbits (similar to 40 visits) of WFC3 observations. and is proved to be able to provide near photon noise limited corrections for observations made with both staring and scanning modes of transiting exoplanets as well as for starting-mode observations of brown dwarfs. After our model correction, the light curve of the first orbit in each visit has the same photometric precision as subsequent orbits, so data from the first orbit no longer need. to. be discarded. Near-IR arrays with the same physical characteristics (e.g., JWST/NIRCam) may also benefit from the extension of this model if similar systematic profiles are observed.

The genes of the Major Histocompatibility Complex (MHC) represent the most diverse genomic region in vertebrates, and has become a paradigm both for adaptively important genetic variation and how balancing selection can act to retain diversity in the face of gene flow. Within this thesis I examined how the natural mating system of a population of sea trout (Salmo trutta) located in a stream in N E Scotland, affected levels of genetic diversity at both neutral microsatellite loci and at the MHC. High levels of multiple mating were observed for both males and females whereby females mated with as many as nine males during one spawning event and often spawned at multiple nests and males mated with as many as nine females. Repeat spawning events including the same mate pairs was common, perhaps indicating mate choice. Indeed majority males (those which sired the highest number of offspring within a nest) sired more MHC divergent offspring than expected under random mating i.e. individual offspring's maternally and paternally inherited MHC sequences contained a higher number of polymorphic sites than expected under random mating. This may indicate a mating strategy whereby disassortative MHC mate choice increases offspring diversity. Although, MHC played a significant role in mate selection¸ no selective effect of MHC diversity or genotype was found to influence offspring survival in c.8 month old parr. However, any affect may be masked by the strong family group structure within the offspring population with clustering of highly related individuals. Selective mating resulting in high individual diversity and high diversity across the offspring cohort may act as a bet hedging mechanism maximising the chances that at least some offspring will be genetically equipped to deal with selective pressures in the environment. The findings of this thesis highlight the complexity of individual mating systems and the implications that mating practices such as multiple mating and mate choice can have on offspring genetic diversity.

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I use Heidegger’s Being and Time to understand and critique racial discourse, but to also determine Heidegger’s reach into issues like racial identity. I start by examining how his introductory statements in Being and Time on the term “existentiell” suggest a path towards a conception of identity. I then go into how a racial identity could, through his terminology, be conceived as what I call a “fear existentiell.” I demonstrate how society assists the individual in maintaining a racialized existence that is embedded in fear. I move toward an examination of Heidegger’s three concepts of death to demonstrate how two of these death concepts (verenden and ableben) are often attached to a racial identity through racial discourse. I move into a discussion that relies on W.E.B. Du Bois’s conception of the black American as a problem for America and, using his seminal question, “How does it feel to be a problem?” I show that the individual’s existence, as discussed in Heidegger, becomes a problem for itself through the racial discourse about its identity. I call this “Being-a-problem.” At first, I discuss it as inauthentic, as it is driven by social fear and generalized discussions about racial identity; however, I later demonstrate how it can move from inauthentic Being-a-problem to authentic Being-a-problem. I end with an analysis of racial discourse, showing that it exemplifies what I call, “race reports,” which are comprised of reports about the individual’s racial identity that conceal a person’s potential for authenticity.

Chronic exposure of humans or rodents to high calorie diets leads to hypertriglyceridemia and ectopic lipid deposition throughout the body, resulting in metabolic disease. Cellular lipids are stored in organelles termed lipid droplets (LDs) that are regulated by tissue-specific LD proteins. These proteins are critical for lipid homeostasis, as humans with LD protein mutations manifest metabolic dysfunction. Identification of novel components of the LD machinery could shed light on human disease mechanisms and suggest potential therapeutics for Type 2 Diabetes. Microarray analyses pinpointed the largely unstudied Hypoxia-Inducible Gene 2 (Hig2) as a gene that was highly expressed in obese human adipocytes. Imaging studies demonstrated that Hig2 localized to LDs in mouse hepatocytes and the human SGBS adipocyte cell line. Thus, this work examined the role of Hig2 as a LD protein in liver and adipose tissue. Hig2 deficiency reduced triglyceride deposition in hepatocytes; conversely, ectopic Hig2 expression promoted lipid deposition. Furthermore, liver-specific Hig2-deficient mice displayed improved glucose tolerance and reduced liver triglyceride content. Hig2 deficiency increased lipolysis and -oxidation, accounting for the reduced triglyceride accumulation. Similarly, adipocyte-specific Hig2-deficient mice displayed improved glucose tolerance, reduced adipose tissue weight and brown adipose tissue that was largely cleared of lipids. These improvements were abrogated when the animals were placed in thermoneutral housing and brown adipocyte-specific Hig2-deficient mice also displayed improved glucose tolerance, suggesting that active brown fat largely mediates the metabolic phenotype of Hig2 deletion. Thus, this work demonstrates that Hig2 localizes to LDs in liver and adipose tissue and promotes glucose intolerance.

Summary in English. / Bibliography: pages 146-169. / The biology, population dynamics, and the environmental tolerances (temperature and light) in laboratory culture, of the endemic intertidal South African fucoid Bifurcaria brassicaeformis (Kütz) Barton have been investigated. A general description is included of the morphology and anatomy, and comparisons made with that of other species in the genus. Studies on plants collected from contrasting habitats on the lowshore and from mid-shore pools revealed that while cortical thickness of vegetative uprights were similar for both habitats, medullary diameters were generally higher, corresponding to generally thicker uprights in the low-shore. Observations on the method of zygote attachment revealed that attachment of the species resembles that of the European Bifurcaria and Halidrys siliguosa which both also display delayed rhizoidal development and initially attach by means of a mucilage secretion of the zygote wall. Observations on receptacle anatomy revealed that size of conceptacles increase from the apex to the base of a receptacle.

This work is a compilation and analysis of ultracool dwarfs (UCDs) and brown dwarfs within 25 parsecs. It supplements the work of Stauffer et al. [2010] who updated the reputable and widely relied upon Third Catalog of Nearby Stars [Gliese & Jahreiß 1991] with revised coordinates and cross-matched each object with the 2MASS point source catalog [Cutri et al. 2003]. I began by incorporating newly discovered (post 1991) cool companions to Gliese-Jahreiß stars that had been previously undetectable. I then expanded the compilation to include isolated UCDs and other nearby systems with at least one UCD component. Multiple systems are a panacea for astrophysical problems: by applying Kepler’s laws, the model-independent mass of brown dwarfs and low mass stars can be determined and hence serve to constrain theory. This work puts this data into context by exploring the history of brown dwarf theory and reviewing open questions concerning their nature.

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