La fixation biologique d’azote (réduction du N2 atmosphérique, non biodisponible, en ammonium (NH3) bioassimilable) est catalysée par la métalloenzyme nitrogénase. Cette enzyme existe sous trois isoformes chez la bactérie du sol Azotobacter vinelandii: les nitrogénases au molybdène (Mo), au vanadium (V) et au fer (Fe). L’acquisition des métaux cofacteurs constitue un paramètre d’intérêt majeur car Mo et V sont fortement complexés à la matrice (matière organique et oxydes) ce qui peut limiter leur disponibilité. Ces travaux ont montré que la présence d’acide tannique et d’oxydes de fer entraîne des changements majeurs dans la gestion des métaux cofacteurs (Mo et V) chez A. vinelandii. Les stratégies d’acquisition des métaux cofacteurs sont fortement modifiées en présence de ces complexants avec (i) un changement important de la quantité des metallophores produits ainsi que (ii) une acquisition simultanée de Mo et V dans des conditions traditionnellement considérées comme non limitantes en Mo. Ceci se traduit par un changement important dans l’utilisation des nitrogénases; les niveaux de transcrits élevés des gènes nifD et vnfD, spécifiques des nitrogénases au Mo et au V respectivement, suggèrent une utilisation simultanée de ces isoenzymes pour assurer la fixation d’azote. Ce projet a permis de mettre en évidence que face à un stress métallique, l’utilisation des isoformes de la nitrogénase par A. vinelandii est un processus plus versatile que précédemment décrit et que le coût d’acquisition des métaux dans ces conditions constitue un facteur important de la régulation de l’activité des nitrogénases. Ceci suggère que les nitrogénases alternatives pourraient contribuer à la fixation d’azote de manière plus importante que présentement admis.

Aufgrund der Tatsache, dass die Wahl der Therapie bei Wirbelfrakturen der Klasse A3 nach Magerl et al. (1994) weiterhin kontrovers diskutiert wird, wurden in dieser Arbeit die Patientenfälle der Abteilung Orthopädie und Unfallchirurgie der Universitätsmedizin Göttingen betrachtet, die im Zeitraum von 2008 bis 2013 eine Wirbelfraktur im Bereich der Brust- und Lendenwirbelsäule erlitten. Das gesamte Kollektiv umfasst 475 Patienten, von denen 266 männlich und 209 weiblich sind. Es wurden objektive Daten wie GDW, Kyphosewinkel und Wirbelkörperhöhenminderung zu fest definierten Zeitpunkten erhoben. Anhand dieser Daten konnte der Verlauf der Stabilität und sowohl der Korrekturgewinn durch die Therapie als auch der Korrekturverlust während der Nachsorge für die jeweiligen Therapiemethoden erfasst werden. Die Therapiemethoden, die hier verglichen werden, sind die konservative Therapie, die Kyphoplastie, die dorsale und die kombiniert dorsoventrale Stabilisierung. Die in der radiologischen Verlaufskontrolle erhobenen Parameter zeigen, dass bei Frakturen der Klassen A1 und A2, die als stabil gelten, die konservative Therapie zu einem guten Ergebnis führt. Bei A3- Frakturen, bei denen in der internationalen Literatur starke Unstimmigkeit darüber besteht, ob diese Frakturen als stabil oder instabil gelten und wie solche Frakturen im allgemeinen zu behandeln sind, bringt die operative Vorgehensweise klare Vorteile. Zudem können bei kombiniert dorsoventraler Operation noch stabilere Ergebnisse erzielt werden. Für die Rotationsfrakturen stellt sich heraus, dass nach der Entfernung des eingebrachten Osteosynthesematerials ein größerer Korrekturverlust eintritt. Abschließend lässt sich sagen, dass bei isolierten Berstungsfrakturen ohne Beteiligung des Bandapparates die Indikation für die kombiniert dorsoventrale Operation häufiger und frühzeitiger gestellt werden sollte. Außerdem sollte beachtet werden, dass bei instabilen Frakturen die Verlängerung der Tragezeit des Fixateurs einen positiven Einfluss auf den Korrekturerhalt hat.

Thèse numérisée par la Division de la gestion de documents et des archives de l'Université de Montréal.

Injury to the medial malleolus, the distal end of the tibia and one of the bones comprising the ankle joint, can occur in various loading scenarios. Open reduction/internal fixation (ORIF) to reattach the malleolar fragment to the proximal tibia can be achieved via various devices, however small fragments are particularly challenging to treat. In this study, computational finite element analysis (FEA) was utilized to investigate the fixation of transverse medial malleolar fractures by two cancellous screws or by a new fixation device, the Medial Malleolar Sled™. Cadaveric testing assessed the performance of the two constructs in both tension and torsion. Following experimentation, the cadaveric study was modeled in SolidWorks and analyzed via FEA to validate the model against the experimental results. Overall, stress analysis was indicative of areas of relatively higher stress concentrations that correlated with failure locations in the experiment. Such results speak to the predictive nature of the tension and torsion models created in the study, and to the general utility of computational modeling for the study of biomechanical systems.

Woody plant expansion has been documented for decades in many different ecosystems, often due to anthropogenic disturbances to the environment and yielding vast changes in ecosystem functioning. While causes and consequences of woody expansion have been well documented, few studies have investigated functional traits of woody species that promote rapid expansion in range. My objective was to determine if hydraulic efficiency confers enhanced photosynthetic efficiency so that functional traits representing light and water use may be possible mechanisms facilitating woody encroachment into grasslands and forest understories. I quantified leaf-level light environment, photosynthetic activity, and hydraulic characteristics of three sympatric broadleaf evergreens of varying leaf life span (Ilex opaca, Kalmia latifolia, and Myrica cerifera) in a deciduous forest understory to understand seasonal intra- and interspecific ranges of broadleaf evergreen physiology. Additionally, I investigated the effects of age on physiological efficiency of M. cerifera across a chronosequence (i.e., space for time substitution) of shrub thicket development in order to understand possible age-related physiological mechanisms facilitating shrub expansion. Lastly, I determined functional traits and resulting physiology that contribute to rapid expansion and thicket formation of an invasive, deciduous, N-fixing shrub, Elaeagnus umbellata, and a native, evergreen, N-fixing shrub M. cerifera. When compared to co-occurring evergreen species, electron transport rate (ETR) of M. cerifera was nearly double that of I. opaca or K. latifolia in summer. Photosynthetic capacity was positively related to hydraulic capacity among understory evergreens. Furthermore, photosynthetic and hydraulic efficiency of M. cerifera remained consistent despite considerable differences in thicket age and development. Both similar and contrasting functional traits of E. umbellata and M. cerifera allowed for enhanced light capture and water movement, and reductions in subcanopy light penetration. Enhanced hydraulic and photosynthetic efficiency relative to co-occurring species contributes to rapid range expansion and thicket formation by promoting enhanced productivity and limiting successful colonization of other species. My results indicate that there may be suites of functional traits linked to expansive success and thicket-formation, yet differences in functional traits between native and invasive species represent alternative strategies leading to rapid growth and thicketization.

In the nutrient-poor soils characteristic of coastal environments, symbiotic association with the nitrogen-fixing root endosymbiont Frankia is essential to establishment and survival of the woody shrub Morella cerifera. Nutrient deficiency quickly becomes severe unless seedlings are infected by Frankia soon after germination. However, the means of arrival of Frankia prior to shrub establishment has not been determined. Using sterilized lab-grown M. cerifera seedlings and fecal samples collected from passerine birds on the Eastern Shore of Virginia, viability of avian dispersal of the bacteria was tested. Although passerine fecal samples did produce nodules on some sterilized M. cerifera seedlings, these experimental inoculations did not lead to significantly higher likelihood of nodulation, relative to sterilized reference seedlings. Non-sterilized seedlings displayed greatest percent nodulation; results suggest that passerines contribute to Frankia dispersal, but also that the actinomycete is contained on or within viable seeds or fruits of M. cerifera, and therefore may be co-dispersed directly from the parent plant.

Shrub expansion in herbaceous ecosystems is emerging as an important ecological response to global change, especially in mesic systems where increases in canopy biomass are greatest. Two consequences of woody encroachment are increases in belowground resources, such as carbon and nitrogen, and reductions in above-ground resources such as light, which affect diversity, community trajectory, and ecosystem function. My objective was to determine how expansion of the nitrogen-fixing shrub Morella cerifera affected the resource environment across a chronosequence of shrub expansion on a Virginia barrier island. I quantified changes in carbon (C) and nitrogen (N) cycling, canopy structure and understory light associated with M. cerifera expansion. Litterfall in shrub thickets exceeded litterfall for other woody communities in the same region, and due to high N concentration, resulted in a return of as much as 169 kg N ha-1 yr-1 to the soil, 70% of which was from symbiotic N fixation. Litter and soil C and N pools were 3-10 times higher in shrub thickets than in adjacent grasslands. Understory light in shrub thickets decreased to as low as 0.5% of above-canopy light. Sunflecks in shrub thickets were shorter, smaller and less intense than sunflecks in forest understories. However, relative to other shrub species such as Elaeagnus umbellata, M. cerifera was less efficient at intercepting light. Although M. cerifera had the highest leaf area index (LAI) of five shrub species studied, M. cerifera was relatively inefficient at light attenuation due to low levels of branching, steep leaf angles and a relatively shallow canopy. The shift from grassland to shrub thicket on barrier islands, and in other mesic systems, results in a significant change in canopy structure that alters understory resource availability and greatly alters ecosystem function and trajectory.

Formaldehyde is widely used fixative. Its advantages are low cost, simplicity of use and good fixation traits, which are fast tissue penetration, good preservation of morphological structures and compatibility with downstream histological applications. Formaldehyde disadvantages are negative effects on nucleic acids. Formaldehyde solutions modify primary structure of deoxyribonucleic acid (DNA), fragment DNA and create protein-DNA covalent bonds that hinder DNA isolation procedures. Level of negative effects of formaldehyde is dependent on many factors. Effect of formaldehyde chemical composition (formaldehyde dilution, presence of buffer or formic acid) and effect of fixation length were studied in this work. On DNA extracted from fixed tissues, DNA quantity and level of DNA fragmentation were studied by quantitative polymerase chain reaction, fluorescence assay for DNA quantification and by on- chip electrophoresis on bioanalyzer Agilent 2100. Quality and quantity of acquired DNA were tested by DNA profile determination for identification purposes using STR (short tandem repeats) analysis. Results show that of all tested fixatives, buffered 4% formaldehyde is the most suited solution in regards of sufficient amount of DNA and sufficient DNA quality. Other formaldehyde variants (non-buffered 4%...

Natural and artificial selection cause changes in certain regions of the genome resulting in selection signatures. Thus, is expected to identify genes associated with the traits under selection in such regions. Selection signatures may be identified using different methodologies, and some are based on detecting of contiguous sequences of homozygous identical-by-descent haplotypes, called runs of homozygosity (ROH), or estimating fixation index (FST) of genomic windows that indicates genetic differentiation. In our study, we aimed to identify selection signatures in a paternal broiler line and to investigate the genes annotated in these regions as well as the biological phenomena involved. For such purpose, ROH and FST-based analysis were performed using whole genome sequence of twenty eight chickens from two different generations. ROH analysis identified homozygous regions of short and moderate length. Analyzing ROH patterns it was observed regions commonly shared among some animals and changes in ROH abundance and length between the two generations. The results also suggests that WGS outperforms SNPchip data, however the number of individuals analyzed must be properly chosen. FST-based analysis revealed genetic differentiation in some genomic windows. Annotation of the consensus regions of ROH and FST windows counted for many genes of which some were previously associated with traits of economic interest, such as APOB, IGF1, IGFBP2, POMC, PPARG, and ZNF423. Overrepresentation analysis of the genes resulted in biological terms of skeletal muscle, matrilin proteins, adipose tissue, hyperglycemia and diabetes, Salmonella infections and tyrosine. Therefore, suggested that ancient and recent selection in TT line acted over regions affecting performance traits. / Identificação de assinaturas de seleção envolvidas com características de desempenho em uma linhagem paterna de frangos de corte Seleção natural e artificial causam mudanças em determinadas regiões do genoma, resultando em assinaturas de seleção. Assim, espera-se identificar genes associados às características sob seleção nessas regiões. Assinaturas de seleção podem ser identificadas usando diferentes metodologias, e algumas delas são baseadas na detecção de sequências contíguas de haplótipos homozigotos idênticos por descendência, chamados segmentos de homozigose (ROH), ou na estimativa do índice de fixação (FST) de janelas genômicas que indicam diferenciação genética. Em nosso estudo, objetivamos identificar assinaturas de seleção em uma linha paterna de frangos de corte e investigar os genes anotados nessas regiões, bem como os fenômenos biológicos envolvidos. Para tal propósito, as análises de ROH e FST foram realizadas usando dados de sequenciamento completo do genoma (WGS) de vinte e oito aves de duas gerações diferentes. A análise de ROH identificou regiões em homozigose de comprimentos curto e moderado. Analisando os padrões de ROH, foram observadas regiões comumente compartilhadas entre alguns animais e mudanças na abundância e no comprimento da ROH entre as duas gerações. Os resultados também sugerem que dados de WGS apresentam vantagens sobre os dados de SNPchip, porém o número de indivíduos analisados deve ser levado em consideração. A análise baseada em FST revelou diferenciação genética em algumas janelas genômicas. Anotação das regiões consenso de ROH e das janelas FST identificaram diversos genes, alguns dos quais já foram associados a características de interesse econômico, como APOB, IGF1, IGFBP2, POMC, PPARG e ZNF423. Análises de enriquecimento dos genes resultaram em termos biológicos de músculo esquelético, proteínas matrilinas, tecido adiposo, hiperglicemia e diabetes, infecções por Salmonella e tirosina. Portanto, sugerimos que a seleção ocorrida durante várias gerações na linha TT atuou sobre as regiões que afetam as características de desempenho destes animais.

Le cycle océanique de l'azote est à l'origine de deux rétro-actions climatiques au sein du système terre. D'unepart, il participe au contrôle du réservoir d'azote fixé disponible au développement du phytoplancton et à lamodulation de la pompe biologique, un des mécanismes de séquestration du carbone anthropique. D'autre part,le cycle de l'azote produit un gaz à effet de serre et destructuer d'ozone, le protoxyde d'azote (N2O). L'évolutionfuture du cycle de l'azote sous l'influence du rechauffement climatique, de la déoxygénation et de l'acidificationdes océans reste une question ouverte. Les processus tels que la fixation d'azote, la dénitrification et laproduction de protoxyde d'azote seront modifiés sous l'influence conjuguée des ces trois stresseurs. Cesinteractions peuvent être évaluées grâce aux modèles globaux de biogéochimie marine. Nous utilisons NEMOPISCESet l'ensemble des modèles CMIP5 pour projeter les modifications des taux de fixation d'azote, denitrification, de production et des flux air-mer de N2O à l'horizon de 2100 en réponse au scénario 'business-asusual'.Les effets liés à l'action combinée du rechauffement climatique et de l'acidification des océans sur leréservoir d'azote fixé, la production primaire et la rétro-action sur le bilan radiatif sont également évalués danscette thèse.! / The marine nitrogen cycle is responsible for two climate feedbacks in the Earth System. Firstly, it modulates thefixed nitrogen pool available for phytoplankton growth and hence it modulates in part the strength of thebiological pump, one of the mechanisms contributing to the oceanic uptake of anthropogenic CO2. Secondly, thenitrogen cycle produces a powerful greenhouse gas and ozone (O3) depletion agent called nitrous oxide (N2O).Future changes of the nitrogen cycle in response to global warming, ocean deoxygenation and oceanacidification are largely unknown. Processes such as N2-fixation, nitrification, denitrification and N2Oproduction will experience changes under the simultaneous effect of these three stressors. Global oceanbiogeochemical models allow us to study such interactions. Using NEMO-PISCES and the CMIP5 modelensemble we project changes in year 2100 under the business-as-usual high CO2 emissions scenario in globalscale N2-fixation rates, nitrification rates, N2O production and N2O sea-to-air fluxes adding CO2 sensitivefunctions into the model parameterizations. Second order effects due to the combination of global warming intandem with ocean acidification on the fixed nitrogen pool, primary productivity and N2O radiative forcingfeedbacks are also evaluated in this thesis.