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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Adaptation of an invasive grass to agriculture: ecological and genomic evidence

Smith, Alyssa Laney 06 June 2017 (has links)
Species vary phenotypically and genetically across their environmental range limits, and this variation can influence ecological processes. Ecologically meaningful intraspecific variation might be particularly important in the context of agricultural weeds and exotic invaders, because intraspecific variation in these species might allow them to rapidly adapt to their unusually dynamic and variable environments. In a greenhouse study, we explored intraspecific variation in the size, rhizome production, and competitive ability of the global invader, Johnsongrass (Sorghum halepense), representing populations from agricultural and non-agricultural habitats across its introduced North American range. We also used these populations to explore the relationship between phenotypic variation and genomic endoreduplication responses to the common stresses herbicides, competition, and clipping. Endoreduplication occurs when plants increase their genome size by increasing their nuclear chromosome number, with some evidence showing correlations with stress response. We found that Johnsongrass plants from agricultural habitats were larger than plants from non-agricultural habitats, but there was no difference between habitats in either rhizome production or competitive ability. Two of the five herbicides we tested, primisulfuron and imazethapyr, had the strongest suppressive effects on Johnsongrass, and also stimulated the greatest rates of endoreduplication. Furthermore, agricultural populations showed higher levels of endoreduplication. We found no overall effect of competition on endoreduplication, although endoreduplication was higher for non-agricultural populations than agricultural populations. When competing with corn, but not with conspecifics, Johnsongrass roots increased endoreduplication by 13%. Clipping induced substantial endoreduplication, but there was no difference between agricultural and non-agricultural populations. Our results suggest that endoreduplication may play a role in some, but not all, stress responses in Johnsongrass. Furthermore, our results indicate that Johnsongrass has adapted in some phenotypic and genomic ways to agricultural habitats in North America. Such adaptation may play a role in this species' success as both an agricultural weed and an exotic invader. / Master of Science in Life Sciences
2

Diversidade intraespecífica em Gracilaria domingensis (Gracilariales, Rhodophyta): estudos fisiológicos na interpretação do polimorfismo de cor / Instraspecific diversity in Gracilaria domingensis (Gracilariales, Rhodophyta): physiological studies on the interpretation of the color polymorphysm

Ferreira, Luciana Bastos 04 December 2008 (has links)
O presente trabalho analisou as fases gametofítica e tetrasporofítica de morfos verde, vermelho e marrons de Gracilaria domingensis em laboratório. A capacidade reprodutiva foi testada considerando-se: i, número de cistocarpos diferenciados; ii, número de carpósporos e tetrásporos liberados; iii, diâmetro desses esporos; e iv, sobrevivência de carpósporos e tetrásporos, esse último em diferentes condições de irradiância, nutrientes, e radiação ultravioleta. A capacidade somática foi testada em diferentes fases do desenvolvimento por meio da análise dos seguintes parâmetros: i, taxas de crescimento em diferentes condições nutricionais; ii, taxas de crescimento em diferentes condições de radiação ultra-violeta; iii, atividade da enzima nitrato redutase em diferentes condições nutricionais; iv, taxas de fotossíntese; e v, síntese de aminoácidos semelhantes a micosporinas (MAAs) em diferentes condições de radiação UV-B. Uma das únicas diferenças observadas na capacidade reprodutiva entre as linhagens foi o maior período de liberação de carpósporos derivados dos cruzamentos envolvendo apenas gametófitos vermelhos. Essa característica disponibilizaria uma maior quantidade de propágulos dessa linhagem, trazendo vantagens competitivas em relação às demais no ambiente natural. Plantas verdes mostraram maiores valores de fotossíntese máxima, maior síntese de MAAs quando expostas à radiação UV-B, e maior teor de proteínas solúveis totais quando comparadas às plantas vermelhas. Essas respostas sugerem adaptações a ambientes oligotróficos e com intensa luminosidade. Foi observada heterose nas linhagens de tetrasporófitos marrons (VmVd ou VdVm) com relação a pelo menos um dos seguintes parâmetros: fotossíntese máxima e eficiência fotossintetizante; taxas de crescimento; conteúdo de proteínas solúveis totais; atividade da NR; e sobrevivência de carpósporos. Esse vigor híbrido, pelo menos quanto a alguns aspectos, favoreceria a manutenção do alelo verde na natureza. As linhagens de tetrasporófitos marrons apresentaram desempenho distinto quando comparadas entre si com relação a sobrevivência de esporos e taxas de crescimento, indicando que os dois genótipos se expressam de forma diferente frente a condições abióticas distintas. O número de carpósporos liberados foi semelhante ao de tetrásporos considerando-se a massa fresca das plantas férteis, porém, a sobrevivência desses últimos foi sempre maior. O desempenho somático e reprodutivo de tetrasporófitos foi maior que o de gametófitos na maior parte das condições testadas, independentemente da linhagem. Esses resultados demonstraram que as diferentes fases do histórico de vida de G. domingensis têm características metabólicas distintas, o que confere às plantas uma maior plasticidade fenotípica. As diferenças detectadas entre as linhagens no presente trabalho foram discretas. Caso as vantagens proporcionadas pelo alelo verde fossem muito superiores às apresentadas pelo alelo vermelho, ou vice-versa, seria esperado que, ao longo do tempo, uma das duas formas excluísse a outra. A coexistência dos morfos, porém, indica que cada um deles deve ocupar um nicho ligeiramente distinto do outro, o que confere à espécie vantagens frente a ambientes heterogêneos e/ou mudanças ambientais, possibilitando uma maior capacidade de adaptação. / This work investigated gametophytic and tetrasporophytic phases of green, red and brown morphs of Gracilaria domingensis in laboratory. The reproductive performance was tested considering the following: i, number of cystocarps produced; ii, number of carpospores and tetraspores released; iii, diameter of these spores; and iv, survival of carpospores and tetraspores in different nutrient, irradiance and UV-B conditions. The somatic performance of different life phases was tested considering the following: i, growth rates on different nutritional conditions; ii, growth rates on different UV-B conditions; iii, nitrate reductase (NR) activity on different nutritional conditions; iv, photosynthetic rates; and v, mycosporine-like amino acids (MAAs) synthesis on different UV-B conditions. Carpospores originated by the cross of red males x red females were released by a longer period of time when compared to the other carpospores strains. This was almost the only difference found in the reproductive performance among different strains, and could make a greater number of the red strain propagules available for settling. This result could represent competitive advantages in the natural environment. Green plants showed greater values of maximum photosynthesis, a greater MAAs synthesis when exposed to UV-B radiation, and greater amounts of total soluble proteins when compared to the red plants. These responses suggest adaptations to high irradiances and oligotrophic environments. Heterosis was observed in one of the two brown tetrasporophyte strains considering, at least, one of the following parameters: maximum photosynthesis and photosynthetic efficiency; growth rates; total soluble proteins content; NR activity; and survival of carpospores. The heterosis related to these aspects could favor the maintenance of the green allele in nature. The two brown tetrasporophytic strains showed different performance considering the survival of spores and growth rates, which indicates that the two genotypes are expressed in different ways depending on the abiotic conditions. The number of spores released was the same for carpospores and tetraspores when expressed by the fresh biomass of the fertile plants. However, survival of tetraspores was always higher. The somatic and reproductive performance of tettrasporphytes were higher than the gametophytes ones for most of the conditions tested, regardless the strain. These results demonstrate that the different life phases of G. domingensis have specific metabolic characteristics, which contributes to a higher phenotypic plasticity of this species. The differences found among the strains were slight. If the green allele promoted very superior advantages when compared to the ones promoted by the red allele, or vice-versa, it would be expected that, within time, one of the two morphs would exclude the other. The coexistence of the morphs, however, indicates that each one of them must occupy a slightly different niche, which provides advantages to the species concerning heterogonous environments, and /or environmental changes, and enable it with a greater adaptative capacity.
3

High thoughput study of biofilm and virulence in Listeria monocytogenes using innovative approaches / Étude à haut débit du biofilm et de la virulence de Listeria monocytogenes en utilisant des approches innovantes

Lee, Bo-Hyung 28 May 2019 (has links)
Listeria monocytogenes est un pathogène d'origine alimentaire à multiples facettes caractérisé par sa capacité d'adaptation dans des conditions défavorables et par sa prolifération dans une vaste gamme d'environnements, du sol aux cellules hôtes des mammifères. L'hétérogénéité génétique de L. monocytogenes se reflète dans sa structure clonale diversifiée, ce qui corrèle, dans une certaine mesure, avec des traits phénotypiques tels que la virulence ou la résistance au stress. La thèse portait sur deux phénotypes les plus éminents, la formation d'un biofilm et le potentiel de virulence, sous différents angles et à l'aide des technologies les plus récentes. Tout au long des études, des grands panels d'isolats ont été utilisés pour représenter la diversité intraspécifique. Stimulants défavorables tels que le choc froid et la privation d'éléments nutritifs induits par l'étape d'adhésion bactérienne. L'ajout de NaCl aux cultures de croissance a stimulé la production de biofilm et, de manière surprenante, il a considérablement intensifié la maturation du biofilm de cellules privées de nutriments. Un degré élevé de variation de la productivité relative du biofilm a été observé parmi les sérotypes, les génotypes, de même que les isolats selon les conditions de culture. Cependant, un certain génotype (complexe clonal 26) a révélé de manière caractéristique une production de biofilm plus élevée à froid (10°C), suggérant une association du génotype avec le phénotype du biofilm. Pan-GWAS a identifié un certain nombre de gènes parmi lesquels ceux impliqués dans des fonctions telles que la ‘transformation/compétence’, les ‘gènes liés aux phages’ et le ‘métabolisme du phosphate’ devront faire l'objet d'études plus approfondies sur leur rôle dans la formation du biofilm. L'analyse du séquençage de l'ARN a révélé une grande hétérogénéité intraspécifique dans les profils de transcriptome basal qui mettaient en évidence le rôle du réseau de régulation, y compris certains facteurs transcriptionnels avec des rôles clés dans la virulence tels que σB, PrfA, et CodY. La plasticité transcriptomique entre les lignées I et II ainsi que les génotypes hyper et hypovirulents ont confirmé les caractéristiques évolutives et épidémiologiques de L. monocytogenes. De plus, la voie métabolique centrale a été impliquée dans l'infection dans le système modèle de Galleria mellonella. En conclusion, la thèse a exploré la diversité intraspécifique de L. monocytogenes et a donné lieu à de nombreux résultats phénotypiques, génomiques et transcriptomiques. Grâce à l'approche intégrative des omiques en listeriologie, le présent travail contribuera à dévoiler la physiologie et la pathogenèse de la bactérie. / Conditions and proliferation in a wide range of environments from soil to mammalian host cells. The genetic heterogeneity in L. monocytogenes is reflected on its diversified clonal structure which correlates, to some extent, with phenotypic traits such as virulence or stress resistance. The thesis investigated two most prominent phenotypes, biofilm formation and virulence potential, from various perspectives using state-of-the art technologies. Throughout the studies, large panels of isolates were used to represent the intraspecific diversity. Unfavourable stimuli such as cold shock and nutrient deprivation induced bacterial adhesion step. Addition of NaCl to growth cultures stimulated biofilm production and, surprisingly, it significantly intensified biofilm maturation of nutrient-deprived cells. High degree of variation in relative biofilm productivity was observed among serotypes, genotypes, as well as isolates across culture conditions, however, certain genotype (clonal complex 26) revealed distinctively higher biofilm production under cold temperature (10°C) suggesting an association of genotype with biofilm phenotype. Pan-GWAS identified a number of genes among which those implicated in functions such as ‘transformation/competence’, ‘phage-related genes’, and ‘metabolism of phosphate’ will need further investigations for their roles in biofilm formation. RNA sequencing analysis revealed high intraspecific heterogeneity in basal transcriptome profiles that featured the role of regulatory network including certain transcriptional factors with key roles in virulence such as σB, PrfA, and CodY. The transcriptomic plasticity between lineage I and II as well as hyper- and hypovirulent genotypes supported the evolutionary and epidemiological characteristics of L. monocytogenes. Moreover, the central metabolic pathway was implicated in the infection in Galleria mellonella model system. Conclusively, the thesis explored intraspecific diversity in L. monocytogenes and resulted in ample phenotypic, genomic, and transcriptomic findings. With the integrative omics approach in listeriology, the present work will contribute to unveiling the physiology and pathogenesis of the bacterium.
4

Diversidade intraespecífica em Gracilaria domingensis (Gracilariales, Rhodophyta): estudos fisiológicos na interpretação do polimorfismo de cor / Instraspecific diversity in Gracilaria domingensis (Gracilariales, Rhodophyta): physiological studies on the interpretation of the color polymorphysm

Luciana Bastos Ferreira 04 December 2008 (has links)
O presente trabalho analisou as fases gametofítica e tetrasporofítica de morfos verde, vermelho e marrons de Gracilaria domingensis em laboratório. A capacidade reprodutiva foi testada considerando-se: i, número de cistocarpos diferenciados; ii, número de carpósporos e tetrásporos liberados; iii, diâmetro desses esporos; e iv, sobrevivência de carpósporos e tetrásporos, esse último em diferentes condições de irradiância, nutrientes, e radiação ultravioleta. A capacidade somática foi testada em diferentes fases do desenvolvimento por meio da análise dos seguintes parâmetros: i, taxas de crescimento em diferentes condições nutricionais; ii, taxas de crescimento em diferentes condições de radiação ultra-violeta; iii, atividade da enzima nitrato redutase em diferentes condições nutricionais; iv, taxas de fotossíntese; e v, síntese de aminoácidos semelhantes a micosporinas (MAAs) em diferentes condições de radiação UV-B. Uma das únicas diferenças observadas na capacidade reprodutiva entre as linhagens foi o maior período de liberação de carpósporos derivados dos cruzamentos envolvendo apenas gametófitos vermelhos. Essa característica disponibilizaria uma maior quantidade de propágulos dessa linhagem, trazendo vantagens competitivas em relação às demais no ambiente natural. Plantas verdes mostraram maiores valores de fotossíntese máxima, maior síntese de MAAs quando expostas à radiação UV-B, e maior teor de proteínas solúveis totais quando comparadas às plantas vermelhas. Essas respostas sugerem adaptações a ambientes oligotróficos e com intensa luminosidade. Foi observada heterose nas linhagens de tetrasporófitos marrons (VmVd ou VdVm) com relação a pelo menos um dos seguintes parâmetros: fotossíntese máxima e eficiência fotossintetizante; taxas de crescimento; conteúdo de proteínas solúveis totais; atividade da NR; e sobrevivência de carpósporos. Esse vigor híbrido, pelo menos quanto a alguns aspectos, favoreceria a manutenção do alelo verde na natureza. As linhagens de tetrasporófitos marrons apresentaram desempenho distinto quando comparadas entre si com relação a sobrevivência de esporos e taxas de crescimento, indicando que os dois genótipos se expressam de forma diferente frente a condições abióticas distintas. O número de carpósporos liberados foi semelhante ao de tetrásporos considerando-se a massa fresca das plantas férteis, porém, a sobrevivência desses últimos foi sempre maior. O desempenho somático e reprodutivo de tetrasporófitos foi maior que o de gametófitos na maior parte das condições testadas, independentemente da linhagem. Esses resultados demonstraram que as diferentes fases do histórico de vida de G. domingensis têm características metabólicas distintas, o que confere às plantas uma maior plasticidade fenotípica. As diferenças detectadas entre as linhagens no presente trabalho foram discretas. Caso as vantagens proporcionadas pelo alelo verde fossem muito superiores às apresentadas pelo alelo vermelho, ou vice-versa, seria esperado que, ao longo do tempo, uma das duas formas excluísse a outra. A coexistência dos morfos, porém, indica que cada um deles deve ocupar um nicho ligeiramente distinto do outro, o que confere à espécie vantagens frente a ambientes heterogêneos e/ou mudanças ambientais, possibilitando uma maior capacidade de adaptação. / This work investigated gametophytic and tetrasporophytic phases of green, red and brown morphs of Gracilaria domingensis in laboratory. The reproductive performance was tested considering the following: i, number of cystocarps produced; ii, number of carpospores and tetraspores released; iii, diameter of these spores; and iv, survival of carpospores and tetraspores in different nutrient, irradiance and UV-B conditions. The somatic performance of different life phases was tested considering the following: i, growth rates on different nutritional conditions; ii, growth rates on different UV-B conditions; iii, nitrate reductase (NR) activity on different nutritional conditions; iv, photosynthetic rates; and v, mycosporine-like amino acids (MAAs) synthesis on different UV-B conditions. Carpospores originated by the cross of red males x red females were released by a longer period of time when compared to the other carpospores strains. This was almost the only difference found in the reproductive performance among different strains, and could make a greater number of the red strain propagules available for settling. This result could represent competitive advantages in the natural environment. Green plants showed greater values of maximum photosynthesis, a greater MAAs synthesis when exposed to UV-B radiation, and greater amounts of total soluble proteins when compared to the red plants. These responses suggest adaptations to high irradiances and oligotrophic environments. Heterosis was observed in one of the two brown tetrasporophyte strains considering, at least, one of the following parameters: maximum photosynthesis and photosynthetic efficiency; growth rates; total soluble proteins content; NR activity; and survival of carpospores. The heterosis related to these aspects could favor the maintenance of the green allele in nature. The two brown tetrasporophytic strains showed different performance considering the survival of spores and growth rates, which indicates that the two genotypes are expressed in different ways depending on the abiotic conditions. The number of spores released was the same for carpospores and tetraspores when expressed by the fresh biomass of the fertile plants. However, survival of tetraspores was always higher. The somatic and reproductive performance of tettrasporphytes were higher than the gametophytes ones for most of the conditions tested, regardless the strain. These results demonstrate that the different life phases of G. domingensis have specific metabolic characteristics, which contributes to a higher phenotypic plasticity of this species. The differences found among the strains were slight. If the green allele promoted very superior advantages when compared to the ones promoted by the red allele, or vice-versa, it would be expected that, within time, one of the two morphs would exclude the other. The coexistence of the morphs, however, indicates that each one of them must occupy a slightly different niche, which provides advantages to the species concerning heterogonous environments, and /or environmental changes, and enable it with a greater adaptative capacity.
5

Patrons de diversité inter- et intraspécifique dans les réseaux dendritiques d'eau douce : implications pour leur fonctionnement et leur conservation / Inter- and intraspecific diversity patterns in dendritic river networks

Fourtune, Lisa 12 January 2018 (has links)
L'objectif de cette thèse a été de caractériser les patrons spatiaux de diversité inter- et intraspécifique au sein des réseaux dendritiques, d'expliciter les processus évolutifs et écologiques qui les sous-tendent, et d'isoler les possibles covariations spatiales et interactions existant entre ces différentes facettes de biodiversité. Pour cela, j'ai tout d'abord développé de nouvelles méthodes statistiques permettant l'analyse, par des modèles causaux, de données sous la forme de matrices de distances, afin de pouvoir analyser plusieurs facettes de biodiversité dans un unique cadre statistique au niveau alpha et bêta. J'ai par la suite étudié de manière intégrative les patrons de diversité interspécifique et intraspécifique génétique d'une part, et intraspécifique génétique et intraspécifique phénotypique d'autre part, au sein du bassin versant Garonne- Dordogne. Enfin, j'ai utilisé un modèle de dynamique éco-évolutive afin d'étudier l'impact de la structure et des gradients environnementaux caractérisant les réseaux dendritiques sur l'adaptation locale au sein de ces réseaux. / The aim of this thesis was to characterized the spatial patterns of inter- and intraspecific diversity within riverine networks, to better understand the ecological and evolutionary processes underlying them and to explore how the different facets of biodiversity interact with one another. First, I developed novel statistical approaches allowing the application of causal modeling to data in the form of pairwise matrices, thus allowing the study within integrative frameworks of several biodiversity facets at the alpha and beta levels. I then studied integratively the patterns of interspecific and intraspecific genetic diversity and of intraspecific genetic and intraspecific phenotypic diversity within the Garonne-Dordogne river basin. Finally, I used an eco-evolutionary metapopulation dynamics model to assess the impacts of the structure and environmental gradients that characterize riverine networks on local adaptation.
6

Rôle écologique de la biodiversité intraspécifique en milieu aquatique / Ecological role of intraspecific diversity in freshwaters

Raffard, Allan 08 January 2019 (has links)
Le déclin actuel de la biodiversité a poussé un grand nombre d’études à s’intéresser aux relations entre la biodiversité et le fonctionnement des écosystèmes. La diversité intraspécifique est une facette centrale de la biodiversité qui permet aux espèces de s’adapter aux variations environnementales et dont l’importance écologique est de plus en plus examinée. A l’aide d’une méta-analyse synthétisant des données sur plusieurs espèces et écosystèmes, nous avons démontré qu’un changement de la diversité intraspécifique peut avoir des conséquences écologiques aussi fortes qu’un changement de la diversité spécifique. Ensuite, au travers d’études empiriques nous avons étudié la diversité fonctionnelle et trophique de populations sauvages de vairons (Phoxinus phoxinus), une espèce de poisson abondante en rivière. Une forte variabilité fonctionnelle et trophique a été montrée entre populations de vairons. Cette diversité était structurée de manière complexe du fait de l’action jointe des conditions environnementales, de facteurs évolutifs et des multiples liens existants entre les traits et la niche trophique. Par ailleurs, nous avons montré expérimentalement que les différences fonctionnelles entre populations de vairons pouvaient engendrer des conséquences écologiques aussi fortes qu’une augmentation de la température. De plus, des populations plus diversifiées génétiquement soutenaient des diversités spécifiques élevées puis augmentaient l’intensité des processus écosystémiques. Ces travaux mettent en évidence que la diversité intraspécifique est une composante essentielle de la biodiversité qui doit être considérée comme un facteur majeur affectant la structure des communautés et le fonctionnement des écosystèmes / Current decline of biodiversity has led to many investigations on the relationship between biodiversity and ecosystem functioning. Diversity within species is a pivotal facet of biodiversity that allows species adapting to environmental conditions, and can have ecological effects. Using a meta-analysis synthetizing data across species and ecosystems, we showed that changes in intraspecific diversity can have ecological consequences as strong as changes in species diversity. Then, we empirically studied the functional and trophic diversity among wild populations of European minnows (Phoxinus phoxinus), a highly abundant freshwater species. We observed a high functional and trophic variability among populations, which was shaped by environmental conditions, evolutionary factors, and covariations linking traits and trophic niche among each other. Additionally, we experimentally demonstrated that functional variation among populations led to ecological consequences as strong as those of warming ecosystem. Finally, we uncovered that high genetic diversity within population sustained higher species diversity and higher rates of ecosystem processes. Overall, this thesis reveals that intraspecific diversity is a fundamental component of biodiversity that should be considered as a strong driver of community and ecosystem dynamics.
7

Production de métabolites secondaires chez Penicillium roqueforti : incidence des facteurs abiotiques et évaluation de l'innocuité / Penicillium roqueforti secondary metabolite production : impact of abiotic factor and safety evaluation

Fontaine, Kévin 17 February 2015 (has links)
P. roqueforti est une moisissure connue comme contaminant des ensilages et des aliments, mais aussi utilisée comme ferment pour la production de fromages à pâte persillée. Cette espèce est également connue pour son potentiel de production de métabolites secondaires à impact positif, comme les arômes, mais aussi à impact négatif, tels que des mycotoxines (dont la roquefortine C -ROQC- et l’acide mycophénolique -MPA-). Dans la première partie de ce travail, l’occurrence de la ROQC, du MPA et de l’aflatoxine M1 (seule mycotoxine réglementée dans les produits laitiers), dans une collection de 86 fromages à pâte persillée de différentes variétés et origines géographiques (15 pays), a été réalisée. Il apparaît que, si l’aflatoxine est inférieure au seuil de détection (LOD) de la méthode, les concentrations en ROQC et MPA sont quant à elles très variables et qu’une co-occurrence de ces mycotoxines existe dans 51% des échantillons testés. Dans la seconde partie, la toxicité de ces mycotoxines sur modèles cellulaires intestinal ou monocytaires a été évaluée. L’étude de cytotoxicité en mono-exposition a permis d’établir des valeurs de référence (CI50); d’autre part, un effet synergique des deux mycotoxines aux plus fortes concentrations testées a été révélé sur la lignée cellulaire intestinale (Caco-2). L’implication du mécanisme apoptotique après une exposition précoce (3 et 6 heures) à la ROQC et/ou au MPA a aussi été mise en évidence sur le modèle THP-1 ainsi qu’une absence d’implication de l’apoptose après 24 heures de mono ou de co-exposition sur modèle intestinal Caco-2. Enfin, dans la troisième partie, une étude de facteurs biotique ou abiotiques pouvant potentiellement moduler la production de ROQC et de MPA a été réalisée. L’évaluation du potentiel mycotoxigénique de 96 souches de P. roqueforti a mis en évidence que le milieu cheese-agar (mimant la composition physico-chimique du fromage) était beaucoup moins favorable que le milieu YES pour la production des deux mycotoxines et une grande variabilité dans la capacité de production des souches a été observée. L’étude de l’influence des facteurs abiotiques a montré qu’une température de 12°C ou une concentration en NaCl de 8% ou encore une atmosphère contenant 5% d’O2 diminuait significativement la production de ROQC et de MPA indépendamment de la croissance, alors que les autres facteurs (pH et présence de précurseurs de la ROQC) n’avaient pas d’effet dans les conditions testées. / P. roqueforti is a mould associated with silage and food contamination but also used as a ripening culture for the production of blue-veined cheese. Moreover, this species is also known for its potential to produce secondary metabolites. These metabolites can have a positive impact (e.g. aromas) or a negative impact (e.g. mycotoxins, including roquefortine C -ROQC- and mycophenolic acid -MPA-). In the framework of this work, we first studied the occurrence of MPA, ROQC and aflatoxin M1 (the only regulated mycotoxin in dairy products) within an 86 blue-veined cheese collection (representing 15 countries). Aflatoxin contents were always below the method detection limit. For MPA and ROQC, concentrations were highly variable and a co-occurrence of both mycotoxins was observed in 51% of the tested samples. Then, the toxicity of the 2 mycotoxins was established on various cell models (intestinal and monocytic). Mono-exposure studies allowed IC50 determination. Moreover, a synergistic effect was observed on Caco-2 cells when MPA and ROQC were used for co-exposure at the highest tested concentrations. While an apoptotic mechanism was observed at early THP-1 exposure stages (3 and 6h), no apoptose occurred for Caco-2 cells after 24 h of mono or co-exposure. Finally, a study of the biotic and abiotic factors potentially modulating P. roqueforti MPA and ROQC production was performed. Mycotoxigenic potential evaluation of 96 de P. roqueforti strains highlighted that a cheese-agar medium (mimicking cheese physico-chemical composition) was less favourable than the synthetic YES medium for mycotoxin production. A large variability in terms of mycotoxin production was also observed among the tested strains. Besides, while a significant effect of the temperature (12°C) and NaCl (8%) and O2 (5%) concentrations was observed on ROQC and MPA production, no significant effect of pH and ROQC amino-acid precursor addition could be detected on the production of both mycotoxins.
8

Diversidade intraespecífica em Gracilaria caudata (Gracilariales, Rhodophyta): estudos genéticos e fisiológicos na interpretação da cor do talo / Intraspecific diversity in Gracilaria caudata (Gracilariales, Rhodophyta): genetic and physiological studies in the interpretation of the thallus color

Santos, Fabiana Marchi dos 23 February 2017 (has links)
Gracilaria. caudata J. Agardh é uma das espécies mais comuns no Oceano Atlântico tropical e subtropical. No nordeste do Brasil a espécie é explotada como uma importante agarófita, onde recentemente foram encontradas variantes de coloração marrom-esverdeada crescendo lado a lado a indivíduos de coloração vermelha (mais comuns) em uma população natural. Este estudo teve por objetivo averiguar a estabilidade e o padrão de herança de cor marrom-esverdeada de indivíduos de G. caudata procedentes de uma população natural, bem como avaliar o desempenho somático e reprodutivo das diferentes fases do histórico de vida, levando-se em consideração indivíduos de coloração marrom-esverdeada e vermelha. A partir de cruzamentos teste foi possível verificar que a coloração marrom-esverdeada é estável e herdável, sendo o padrão de herança dessa coloração do tipo nuclear codominante, em que tetrasporófitos homozigotos são vermelhos (vmvm) ou marrom-esverdeados (meme) e os heterozigotos apresentam o fenótipo marrom (vmme e mevm). Variantes pigmentares, independentemente da fase do histórico, atingiram precocemente a maturidade reprodutiva quando comparadas a espécimes do tipo selvagem. Essa característica pode favorecer a manutenção da variante marrom-esverdeada na natureza. No entanto, apesar da diferenciação tardia de cistocarpos, gametófitos femininos, provenientes de tetrasporófitos vmvm, apresentaram um melhor desempenho reprodutivo em relação a gametófitos femininos provenientes de tetrasporófitos com variação pigmentar (meme, vmme e mevm); essa característica poderia contribuir para a predominância de espécimes selvagens na natureza. Entretanto, tetrasporófitos com variação pigmentar não só atingiram precocemente a maturidade reprodutiva como se tornaram mais férteis em relação ao tipo selvagem. Apenas na descendência de tetrasporófitos selvagens (vmvm) foi observada a proporção sexual esperada, entre gametófitos femininos e masculinos. Na progênie de tetrasporófitos com variação pigmentar foram observadas alterações na proporção sexual, devido à presença de gametófitos bissexuais. Essa condição de bissexualidade, provavelmente, é decorrente da presença de um alelo recessivo denominado bi, o qual possibilitaria a expressão de funções femininas em gametófitos masculinos. No presente estudo, pudemos evidenciar que a bissexualidade em G. caudata é herdável, e que gametófitos femininos que portam a mutação bi foram capazes de transmitir a mutação aos descendentes, porém o alelo não é fenotipicamente detectável. Como não foram observados gametófitos bissexuais na descendência de tetrasporófitos vmvm (provenientes do cruzamento feminino vm x masculino vm) sugere-se que a mutação bi estaria presente apenas em tetrasporófitos marrom-esverdeados oriundos da natureza. No entanto, permanece a possibilidade de ocorrência de espécimes bissexuais de coloração vermelha em populações naturais, já que tais indivíduos foram observados na progênie de tetrasporófitos vmme e mevm, indicando assim, que não há ligação entre a bissexualidade e a coloração do talo. Gametófitos femininos vermelhos apresentam melhor desempenho somático quando comparados a gametófitos femininos marrom-esverdeados. Esse aspecto foi evidenciado por meio de taxas de crescimento, número de ápices diferenciados e percentual de fixação ao frasco de cultura. Essas características devem contribuir para a predominância de espécimes do tipo selvagem na natureza. Gametófitos marrom-esverdeados, em contrapartida, apresentaram melhor desempenho fotossintetizante, o que poderia representar uma vantagem, considerando-se o ambiente heterogêneo de ocorrência da espécie, e desse modo, contribuir para a manutenção dessa variante em população natural. Entretanto, não foram observadas diferenças com relação às taxas crescimento entre tetrasporófitos dos quatro genótipos (vmvm, meme, vmme e mevm), apesar das diferenças quanto à fertilidade, concentração pigmentar, número de ápices diferenciados e desempenho fotossintetizante. Tais tetrasporófitos apresentaram taxas de crescimento semelhantes às observadas para gametófitos femininos marrom-esverdeados, apesar do melhor desempenho fotossintetizante desses últimos. Os dados obtidos nesse trabalho sugerem que a variante marrom-esverdeada apresente vantagens adaptativas para G. caudata / Gracilaria caudata J. Agardh is one of the most common species in the tropical and subtropical Atlantic Ocean. In the northeast of Brazil the species is exploited as an important agar producer, where greenish-brown color variants have recently been found growing side by side with individuals of red color (more common) in a natural population. The aim of this study was to investigate the stability and pattern of green-brown inheritance of G. caudata individuals from a natural population, as well as to evaluate the somatic and reproductive performance of the different stages of life history, considering individuals of greenish-brown and red colors. From test crosses it was possible to verify that the greenish-brown color is stable and inheritable. Codominant nuclear inheritance was found in the greenish-brown strains. Homozygous tetrasporophytes are red (rdrd) or greenish-brown (gbgb) while heterozygous tetrasporophytes present the brown phenotype (rdgb and gbrd). Color variants, regardless of the history phase, reached early reproductive maturity when compared to wild type specimens. This feature may favor the maintenance of the greenish-brown variant in nature. However, in spite of the late differentiation of cystocarps, female gametophytes derived from rdrd tetrasporophytes had a better reproductive performance in relation to female gametophytes from tetrasporophytes with color variation (gbgb, rdgb and gbrd); this feature could contribute to the predominance of wild specimens in nature. However, tetrasporophytes with color variation not only reached reproductive maturity early but also became more fertile in relation to the wild type. The expected sexual ratio between female and male gametophytes was only observed in the offspring of wild tetrasporophytes (rdrd). There were changes in the sexual proportion in the progeny of tetrasporophytes with color variation due to the presence of bisexual gametophytes. This condition of bisexuality is probably due to the presence of a recessive allele called bi, which would allow the expression of female functions in male gametophytes. In the present study, we could show that bisexuality in G. caudata is inheritable, and that female gametophytes, which carry the bi mutation, were able to transmit the mutation to the offspring, but the allele is not phenotypically detectable. As no bisexual gametophytes were found in the offspring of rdrd tetrasporophytes (from the cross female rd x male rd), it is suggested that the bi mutation would only be present in brown-green tetrasporophytes from the natural population. However, it remains the possibility of occurrence of bisexual specimens of red color in natural populations, since such individuals were observed in the progeny of tetrasporophytes rdgb and gbrd, thus indicating that there is no link between bisexuality and the thallus color. Red female gametophytes show better somatic performance when compared to the greenish-brown female gametophytes. This aspect was evidenced by means of growth rates, number of differentiated apices, and percentage of attachment to the culture flask. These characteristics should contribute to the predominance of wild type specimens in natural populations. Otherwise, the greenish-brown gametophytes showed better photosynthetic performance, which could represent an advantage considering the heterogeneous environment of the species occurrence, thus contributing to the maintenance of this variant in the natural population. However, no differences were observed among tetrasporophytes of the four genotypes (rdrd, gbgb, rdgb and gbrd), regarding the growth rates, despite of the differences in fertility, pigment concentration, number of differentiated apices, and photosynthetic performance. These tetrasporophytes presented similar growth rates to those observed for greenish-brown female gametophytes, despite of the better photosynthetic performance of the latter. The data obtained in this work suggest that the greenish-brown variant presents adaptive advantages for G. caudata

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