Dissertationen zum Thema „Adaptation des pathogènes“
Geben Sie eine Quelle nach APA, MLA, Chicago, Harvard und anderen Zitierweisen an
Machen Sie sich mit Top-32 Dissertationen für die Forschung zum Thema "Adaptation des pathogènes" bekannt.
Neben jedem Werk im Literaturverzeichnis ist die Option "Zur Bibliographie hinzufügen" verfügbar. Nutzen Sie sie, wird Ihre bibliographische Angabe des gewählten Werkes nach der nötigen Zitierweise (APA, MLA, Harvard, Chicago, Vancouver usw.) automatisch gestaltet.
Sie können auch den vollen Text der wissenschaftlichen Publikation im PDF-Format herunterladen und eine Online-Annotation der Arbeit lesen, wenn die relevanten Parameter in den Metadaten verfügbar sind.
Sehen Sie die Dissertationen für verschiedene Spezialgebieten durch und erstellen Sie Ihre Bibliographie auf korrekte Weise.
Guillemet, Martin. „The dynamics of viral adaptation : theoretical and experimental approaches“. Electronic Thesis or Diss., Université de Montpellier (2022-....), 2023. http://www.theses.fr/2023UMONG020.
Der volle Inhalt der QuelleMost living organisms on the tree of life can be infected by viruses. The ubiquity of viruses is driven by different factors including high mutation rates, high population sizes and low generation times, which allow for quick adaptation to very different host species. The dynamics of adaptation - the rate of change of the mean fitness of the viral population - results from the interplay between multiple evolutionary forces that may promote or hamper viral adaptation. But the interactions between these different factors may often be difficult to understand. During this PhD we developed a combination of theoretical and experimental approaches to disentangle the influence of some of these factors on viral adaptation.First, we explored the dynamics of viral adaptation to a homogeneous host population. We used Fisher’s Geometric Model of adaptation and studied the joint evolutionary and epidemiological dynamics of a viral population spreading in a host population. This modeled allowed us to explore the lethal mutagenesis hypothesis: is it possible to treat viral infections with mutagenic drugs to increase the mutation load of the viral population beyond a threshold that may result in the extinction of the within-host population? We show which parameters affect the critical mutation rate leading to viral extinction and we show how epidemiology and evolution can affect the transient within-host dynamics of the viral population when a single virus life-history trait (transmission rate) is under selection. We extend this modeling framework to study the joint evolution of transmission and virulence during the adaptation of an emerging pathogen. At the beginning of an epidemic, these two traits are expected to evolve independently but a trade-off may build up with viral adaptation.Second, we studied viral adaptation in heterogeneous host populations when the virus spreads among a diversified population of resistance host. We studied the evolutionary emergence of viruses: can viruses avoid extinction by the acquisition of escape mutations allowing them to infect some of the resistant hosts in the population? We developed a simple birth-death process to predict the probability of evolutionary emergence as a function of the composition of the host population. In particular, we show how the proportion of multiple resistant hosts can reduce the risk of pathogen evolutionary emergence. We put some of these predictions to the test using bacteriophages spreading in bacterial populations. We manipulate the diversity of CRISPR immunity in Streptococcus thermophilus bacteria and we confirm the key influence of multiple resistance on the risk of viral adaptation.Third, we also studied viral adaptation in time-varying environments where the host population is allowed to coevolve with the virus. In this experimental project we monitored the adaptation of bacteriophages as they coevolved with the CRISPR immunity of S. thermophilus bacteria. We track reciprocal adaptive changes in which bacteria acquire new layers of resistance (new spacers in the CRISPR array) and phages acquire new escape mutations in the corresponding protospacers. This experiment allows us to monitor the dynamics of viral adaptation across time and space. Interestingly, we find a significant asymmetries in competitive abilities among different bacterial strain in the absence of phage predation. This asymmetric competition has dramatic consequences on the maintenance of diversity of host resistance and on the coevolutionary dynamics with the virus. This thesis demonstrates the possibility to use experimental evolution with microbial microcosms to explore the validity of some theoretical predictions on the dynamics of viral adaptation. This experimental validation is particularly important if one wants to use evolutionary models to make public-health recommendations
Michon, Anne-Laure. „Les témoins de l'adaptation des bactéries pathogènes opportunistes associées à la mucoviscidose : des opérons ribosomiques aux implications thérapeutiques“. Thesis, Montpellier 1, 2013. http://www.theses.fr/2013MON13501/document.
Der volle Inhalt der QuelleBacterial microbiotae and human beings developed mutualist interactions. All disrupting factors impacting this equilibrium can modify relationships among microbiota members with diverse consequences. In such an unstable context, opportunistic bacterial pathogens (OBPs) of endogenous or environmental origin showing great adaptability may find favorable conditions leading to ecological niche extension or to new niche colonization. This is illustrated by the diversity of atypical bacteria as well as by genetic and genomic evolution of members of the cystic fibrosis (CF) respiratory tract (CFRT) microbiota. The deficit in local innate immunity allowed colonization by endogenous and exogenous bacteria that will further develop adaptation processes to this particular ecological niche. The aim of this study was to evaluate phenotypic, genetic and genomic potential adaptation markers in different models of OBPs, particularly in CF. For this purpose, we described the variability in the multiple rrs gene copies using PCR and temperature-based denaturing electrophoresis (PCR-TTGE) on large collections of Veillonella (n=149) and Achromobacter xylosoxidans (n=164), as well as on isolates of six other species involved in the CFRT colonization (Pseudomonas aeruginosa, Stenotrophomonas maltophilia, Staphylococcus aureus, Haemophilus influenzae, Moraxella catarrhalis and Streptococcus pneumoniae). Genome dynamics of 90 isolates from 12 patients chronically colonized by A. xylosoxidans was studied by PCR-TTGE, restriction fragment length polymorphism analysis after pulsed-field gel electrophoresis and PCR on repetitive sequences. Finally, the effect of environmental stress was evaluated on part of the growing CF microbiota and a thorough study of NaCl effect on 85 CF P. aeruginosa isolates was performed.These different approaches highlight: i) the intragenomic heterogeneity of the rrs gene copies in Veillonella (74% of isolates), H. influenzae (61%), S. maltophilia (38%), A. xylosoxidans (28%), and S. aureus (17%), ii) a clonal chronic colonization with A. xylosoxidans in 12 CF patients associated with rrs genetic and/or genomic intra-clonal evolution, iii) the effect of environmental stress such as salinity, pH and temperature on the CFRT microbiota, iv) the antimicrobial effect of NaCl on CF P. aeruginosa isolates, a 6% NaCl concentration inhibiting the growth of all the isolates and a bactericidal action being observed for 90% of the isolates with 10% NaCl, v) multiple effects of NaCl on growth, biofilm and mobility of P. aeruginosa. This study shows that rrs genes and genome dynamics witness for bacterial adaptability within microbiota according to environmental constraints and underlines the diversity and importance of adaptation processes in the long-term pathological adapted microbial communities of the CFRT. Modification of environmental factors such as salinity or pH of the CFRT niche may impact the microbiota and should be considered as targets for CF therapeutics
Talagrand, Emilie. „Diversité, complexité et adaptation au comportement pathogène au sein du genre Aeromonas“. Thesis, Montpellier, 2017. http://www.theses.fr/2017MONTT123/document.
Der volle Inhalt der QuelleAeromonas groups ubiquitous bacteria mainly living in aquatic environments. These opportunistic pathogens for human and numerous animals have a large repertoire of virulence-associated factors. Although pathotypes were proposed and despite some species are more frequently isolated in human and animal infections, their pathogenicity is still poorly understood, mostly because very few comprehensive functional studies are available and because investigations taking into account the genetic diversity and the biological complexity within the genus are lacking.We assumed that for an opportunistic bacterial pathogen of environmental origin as versatile and ubiquitous as Aeromonas, the population structure in complex of species, the outstanding genetic/genomic diversity, the polymorphism of virulence factors and the interactions within pathogenic populations can act as factors driving the adaptation to a pathogenic behaviour. To test this hypothesis, we studied i) the diversification within “A. media”, a complex of species used as a model by a population study that included multilocus genetics, phylogenetics, evolutionary features, comparative genomics, as well as phenotypics, lifestyle and habitat ii) the patho-genomics of well-known virulence factors in aeromonads (aerolysin, thermolabile and thermostable enterotoxins, exotoxin A, serine protease, components and effectors of type III secretion system, and lateral flagellin) in a population that is representative of the known taxonomic diversity in the genus (30 species) and iii) the pathogenic behaviour using an in vivo model (Caenorhabditis elegans), an in vitro model (cytotoxicity, cytoadhesion, biofilm production, motility), and intercellular signals production (type I quorum-sensing) for populations involved in mixed aeromonosis, i.e. 5% of human aeromonosis defined by the isolation of at least 2 distinct clones.The phenomenon of speciation described in the complex “A. media” that aggregates 3 genomic species demonstrates that Aeromonas harbours a population structured in complexes of closely related species whose genetic and genomic diversity, as well as evolution mode (mutations and recombinations) reveal a wide adaptative and patho-adaptative potential linked to lineage emergence. Among the complex “A. media”, the species A. rivipollensis seems to be more adapted to a host-associated lifestyle and harbours specific genes for the resistance to environmental stress. Aeromonas has a wide range of virulence-associated genes, which presented diverse evolutive history. Some of them display a phylogeny linked to the core-genome evolution. These results suggest that these genes are involved in speciation processes probably related to niches adaptation. The evaluation of performances of virulence PCRs revealed major lacks of sensitivity of tested methods mainly due to the genetic polymorphism of the virulence factors. By using in vivo models and in vitro models, we also showed that Aeromonas mixed populations recovered from clinical samples could change the course of infection, likely through a cooperative or competitive mechanism that involves cell-to-cell signalling.The high complexity of Aeromonas results from its population structure, virulence factors polymorphism and multicellular behaviours. They are all putative adaptation factors to a pathogenic behaviour that may explain at least partially the difficulties encountered to elucidate pathogenicity of these bacteria
Dionne, Mélanie. „Variation génétique et potentiel d'adaptation locale chez le saumon atlantique, Salmo salar : structure de population, adaptation immunitaire et résistance aux pathogènes“. Thesis, Université Laval, 2008. http://www.theses.ulaval.ca/2008/25929/25929.pdf.
Der volle Inhalt der QuelleOne of the central endeavors in evolutionary ecology is to understand the mechanisms responsible for natural biodiversity. Biodiversity is defined as the combined diversity of ecosystems, species, populations and the genetic diversity within a given species. Even within a species, a wide diversity of phenotypes and genotypes is often observed, resulting from the interaction between natural selection, gene flow, genetic drift and mutations. The central objective of this thesis was to assess the genetic variability and evaluate the potential for local adaptation in wild Atlantic salmon, Salmo salar. Analyses of neutral molecular markers in 51 salmon rivers revealed a hierarchical genetic structure and suggested the existence of seven regional groups in Québec, Labrador and New-Brunswick, Canada. Landscape genetic analyses suggested a predominant influence of gene flow and thermal regime adaptation in maintaining genetic differentiation. Indirect evidence also suggested that immigrants from a different regional group were less successful in establishing in the new environment compared to residents. Different extents of genetic structure were also found within some river systems, questioning the river-based management approach in Atlantic salmon. Large scale genetic variability at an immuno-competence gene, the Major Histocompatibility Complex (MHC) class IIβ gene, revealed that genetic diversity increased with increasing temperature and bacterial diversity in rivers contrary to patterns with neutral microsatelite markers. This increase in MHC diversity with temperature was more pronounced at the peptide-binding region involved in pathogen binding than at other molecular sites. These results agree with the hypothesized influence of temperature-associated pathogen diversity on local adaptation in Atlantic salmon. Finally, pathogen infections in juvenile salmon were found to be more frequent at the beginning of the summer in southern rather than northern rivers, in concordance with pathogen selection pressure in the wild. A predominant and possibly introduced pathogen, a myxozoa of the genus Myxobolus, was identified in juvenile salmon and two MHC alleles were found to be associated with resistance and susceptibility to that infection, suggesting the importance of MHC standing genetic variation for facing pathogens in a changing environment. This thesis contributes to our understanding on mechanisms maintaining genetic variability and influencing local adaptation in wild Atlantic salmon through analyses in landscape genetics, genetic population structure and patterns of spatio-temporal infectivity in nature.
Thézé, Julien. „Diversification et adaptation génomique des virus entomopathogènes“. Thesis, Tours, 2013. http://www.theses.fr/2013TOUR4006.
Der volle Inhalt der QuelleAt different timescales, the purpose of my PhD was to understand insect virus evolution through the study of the genomic diversification and adaptation of insect large DNA viruses. Firstly, I was able to estimate the ages of baculovirus and nudivirus diversifications, and to propose a long-term coevolutionary scenario between these viruses and their insect hosts. Then, on a narrower timescale, I showed that insect hosts are the major factor in baculovirus diversification, and surprisingly, I also observed that the virus biotic environment, i.e. insect host plants, plays a central role in their evolution. Secondly, punctual mutations have been linked to the local adaptation of differentiated populations of the baculovirus SeMNPV. Finally, the study of convergent genomic adaptation between entomopoxviruses and baculoviruses highlighted that horizontal gene transfers are an important source of variability for large DNA viruses, for the adaption to the same ecological niches. Genes and mechanisms identified in this PhD work provide new insights to understand how genomes are shaped by ecology
Aujoulat, Fabien. „Adaptation et spécialisation des bactéries environnementales à l'infection humaine : étude des genres Ochrobactrum et Agrobacterium“. Thesis, Montpellier 1, 2012. http://www.theses.fr/2012MON13501/document.
Der volle Inhalt der QuelleThe opportunistic bacterial pathogens (OBP) cause the main part of bacterial infectious diseases. Environmental-borne OBP should encounter dramatic changes in lifestyle in order to colonize human beings. The conditions of this adaptation should precise concepts about OBP and emerging pathogens.The genera Ochrobactrum and Agrobacterium groups bacteria with versatile lifestyles that establish diverse relationships with the eukaryotic cells. These environmental-borne OBP caused diverse infectious diseases in immune-compromised patients. In this study, we undertook an approach of multilocus genetic on large population of environmental and clinical strains of Ochrobactrum and Agrobacterium. The population structures were compared to phenotypic traits related to adaptation and virulence in man, such as growth temperature, biofilm formation and virulence tested in Caenorhabditis elegans and human macrophages models.Ochrobactrum anthropi and Ochrobactrum intermedium are the two main Ochrobactrum species to be involved in human diseases. O. anthropi displays an epidemic population structure organized in two large clonal complexes (CCs). CC4 groups only human associated strains whereas CC1 contain environmental and clinical strains. Population genetics suggested that CC4 is a human-associated clone although phenotypic, genomic and virulence traits do not differ between CC1 and CC4 strains.As O. anthropi, O. intermedium displays a high genetic diversity without correlation between the genetic structure and the origin of strains. The level of genetic diversity among clinical strains appears as high as observed in the whole population. Several data such as a low level of genomic diversity suggested that O. intermedium is associated to a narrow ecological niche. The low number of environmental strains described for this species as well as an optimal growth at 37°C suggested that human beings could be the main niche for O. intermedium. Virulence in macrophage and C. elegans models showed diverse behaviour whereas some strains are able to survive and multiply in macrophages model.Multilocus genetics in a population of Agrobacterium spp. that displays diverse lifestyles, revealed a human associated population as observed for O. anthropi. The clinical genovar A7 groups 80% of the clinical strains included in the study, this strains growing at 42°C. Data obtained in this study will be confronted to the knowledge about other environmental-borne OBP such as Pseudomonas aeruginosa, Stenotrophomonas maltophilia and bacteria belonging to the species complex Burkholderia cepacia. All these bacteria displayed sub-populations associated to man or to a particular human disease. These sub-populations suggest a specialization process that will be described in the context of the speciation of bacterial pathogen in order to revisite the concept of « opportunisme infectieux »
Tollenaere, Charlotte. „Génétique et évolution du rat noir (Rattus rattus), réservoir de la peste à Madagascar“. Montpellier 2, 2009. http://www.theses.fr/2009MON20205.
Der volle Inhalt der QuelleSelective pressure applied by pathogens can lead to extremely rapid evolutionary changes on their hosts. It could be the case for the black rat (Rattus rattus), which presents populations resistant to plague (Yersinia pestis infection), where plague have been endemic since about one century, whereas low altitude zone (where the disease is absent) populations are plague susceptible. The black rat is the only possible plague reservoir in Madagascar. This work aims to study plague resistance in R. Rattus, as this trait has important consequences for the disease transmission and maintenance. Neutral genetic patterns agree with a unique colonization of Madagascar by the the black rat, 1000-2000 years ago, from Arabian Peninsula. As for humans, rat settlement would have begun by coastal regions, and latter expanded to the central highlands. Experimental work (controlled infestations and crosses) allowed the study of the resistance phenotype and its offspring transmission. Resistance level variation between plague focus and plague-free zone was confirmed and extended to other localities. Finally candidate gene and genomic approaches lead to detect genetic markers potentially undergoing divergent selection between plague focus and plague free zone than neutral loci and/or associated with experimental plague challenge issue
Saillant, Vincent. „Comprendre le mécanisme du système senseur d’hème des bactéries pathogènes, une cible antibiotique innovante A novel Enterococcus faecalis heme transport regulator (FhtR) is a heme sensor in the gastrointestinal tract“. Thesis, université Paris-Saclay, 2020. http://www.theses.fr/2020UPASB023.
Der volle Inhalt der QuelleHeme, a porphyrin containing an iron atom, is an essential cofactor of several bacterial functions. Heme is also toxic because of the reactivity of the iron generating reactive oxygen species. One of the main mechanisms of heme detoxification, in Gram-positive bacteria, relies on the expression of a heme efflux ABC transporter, HrtBA. The regulation of this transporter has been investigated in two opportunistic pathogens, Enterococcus faecalis and Staphylococcus aureus, two bacteria responsible for multiresistant nosocomial infections. In E. faecalis, a new TetR family regulator, FhtR, has been identified and characterized. The FhtR dependent transcriptional inhibition of hrtBA is lifted by its binding to heme. FhtR controls the intracellular heme pools as showed par the activity of the endogenous heme dependent catalase, KatA. FhtR is thus a master regulator of heme intracellular homeostasis in E. faecalis. In a mouse model of intestinal transit, HrtBA is expressed, demonstrating the relevance of this system in the gastrointestinal tract where E. faecalis is a commensal resident. In S. aureus, hrtBA transcription is controled by the two-component system, HssRS. The study of the mechanism of the membrane heme sensor HssS showed that the intracytoplasmic of the histidine kinase was responsible of the binding and heme signal transduction for HrtBA expression. Alltogether, these results demonstrate that while HrtBA is conserved among Gram positive bacteria, the regulating mechanisms leading to its expression are varied. This suggests that the host heme response is dependent of the bacteria lifestyle and underlies the importance of this cofactor in the host-pathogen relationship. Inhibiting heme effux by HrtBA or the heme sensing mechanisms could lead to new antibiotic strategies
Abad, Pierre. „Aspects moléculaires des mécanismes de résistance chez Nicotiana tabacum en réponse à des agressions induites par des agents pathogènes ou abiotiques“. Paris 11, 1986. http://www.theses.fr/1986PA112289.
Der volle Inhalt der QuellePaul-Pont, Ika. „Sensibilité et adaptation de populations de bivalves marins soumis à des stress multiples : infestation parasitaire, contamination microbienne et pollution métallique“. Thesis, Bordeaux 1, 2010. http://www.theses.fr/2010BOR14008/document.
Der volle Inhalt der QuelleIn coastal ecosystems, man-mediated activity and natural context induce a ?multistress? situation in aquatic organisms. Amongst potential perturbation sources, three of them were studied: metal contamination, bacterial infection and parasite infestation. An integrated approach of their interactions on genetic, protein, cellular and population dynamics responses in the cockle (Cerastoderma edule) and the Manila clam (Ruditapes philippinarum) was undertaken through field and laboratory studies. A two-years monitoring was conducted in four bivalve populations from different environments to estimate the fitness of populations (parameters of population dynamics), in relation with the baseline levels of stressors (metals, parasites) and with the adaptive responses implemented by bivalves in terms of detoxification and immunity. This approach allowed describing different scenarii concerning the relationship between bivalve populations and their environment. In laboratory, co-infection experiments (trematode parasite Himasthla elongata, bacteria Vibrio tapetis) were conducted on these populations in controlled condition with or without metal contamination (cadmium). They showed that the response of bivalves to stress is species-dependent. Combinations were not intuitively deduced from the "mono - stress" responses underscoring the concept of interactions. Despite the complexity and diversity of these interactions, some mechanisms predominated regardless of the studied species. While parasite infestation was not modulated by the presence of metal or bacteria in the environment, metal bioaccumulation in turn was strongly influenced by the presence of one or several pathogens. Beyond disrupting the accumulation of pollutants, the presence of pathogens interfered with the cellular detoxification mechanisms including impairment of the metallothionein (MT) synthesis. A focus on the response of MT in cockles exposed to a metal through the expression of isoform Cemt1 and protein synthesis confirmed the complementary of these observations (gene and protein). They also highlighted the need to analyze responses at different scales to obtain an overview of existing interactive process between pollutants and pathogens. Strong interactions were found: ?Cd x parasite? in the cockle and" bacteria x parasite "in the clam, at the genetic, protein and immune levels. Finally, these experiments highlighted the important role of life history on the sensitivity of organisms to pollutant-pathogen interactions
Rager, Marie-Noëlle. „Apport de la résonance magnétique nucléaire à l'étude du métabolisme bactérien“. Paris 11, 2006. http://www.theses.fr/2006PA114830.
Der volle Inhalt der QuelleKnowledge of metabolic features of each bacterial species is of major interest in the medical, environmental and biotechnological fields. This work shows the contribution made by NMR to the investigation of metabolic diversity notably thanks to its overall and noninvasive approach. Sugar metabolism was studied on Plesiomonas shigelloides, Pasteurella multocida, Aeromonas hydrophila and Escherichia coli. 13C NMR allowed us to characterize transport systems, metabolic pathways and flux. 31P NMR allowed us to study cellular energetic state evolution, enzymatic activities and to characterize regulation factors. Thus, new metabolic pathways could be described. These approaches were applied for the study of bacteria on various states: culturable, nonculturable and encapsulated in silica gel
Tamisier, Lucie. „Adaptation des populations virales aux résistances variétales et exploitation des ressources génétiques des plantes pour contrôler cette adaptation“. Thesis, Avignon, 2017. http://www.theses.fr/2017AVIG0696/document.
Der volle Inhalt der QuellePlants carrying major resistance genes have been widely used to fight against diseases. However, the pathogensability to overcome the resistance after a few years of usage requires the search for efficient and durable resistances.The objectives of this thesis were (i) to identify plant genomic regions limiting pathogen evolution by inducinggenetic drift effects and (ii) to study the impact of the evolutionary forces imposed by the plant on the pathogenability to adapt to resistance, the goal being to further use these forces to limit pathogen evolution. The pepper(Capsicum annuum) – PVY (Potato virus Y) pathosystem has been mainly used to conduct these researches.Regarding the first objective, quantitative trait loci (QTL) were mapped on a biparental pepper population andthrough genome-wide association on a pepper core-collection. These approaches have allowed the detection ofgenomic regions on chromosomes 6, 7 and 12 controlling viral effective population size during the inoculationstep. Some of these QTLs were common to PVY and CMV (Cucumber mosaic virus) while other were virusspecific.Moreover, the QTL detected on chromosome 6 colocalizes with a previously identified QTL controllingPVY accumulation and interacting with a QTL affecting the breakdown frequency of a major resistance gene.Regarding the second objective, a correlation analysis between the evolutionary forces imposed by the plant andan experimental estimation of the durability of a major resistance gene has been done. Experimental evolution ofPVY populations on plants contrasted for the levels of genetic drift, selection and virus accumulation they imposedhas also been performed. Both studies demonstrated that a plant inducing a strong genetic drift combined to areduction in virus accumulation limits virus evolution and could even lead to the extinction of the virus population.These results open new perspectives to deploy plant genetic factors directly controlling pathogen evolutionarypotential and could help to preserve the durability of major resistance genes
Pham, Hoang-Nam. „Impact des métabolites secondaires de plantes sur des bactéries pathogènes de la rhizosphère : existe-t-il un lien entre la résistance sur métaux et la modulation de résistance aux antibiotiques ?“ Thesis, Toulouse 3, 2017. http://www.theses.fr/2017TOU30153/document.
Der volle Inhalt der QuelleThe objective of this thesis is to evaluate the modification of plant secondary metabolism production contaminated with metallic trace elements (MTE) and its consequences on the associated rhizospheric bacterial communities including bacteria presenting MultiDrug Resistant (MDR) phenotypes. We have focused on two contexts of metals exposure: the phytoremediation of mining sites in Vietnam and the reconversion of agricultural soils contaminated by the atmospheric re-deposition of metallurgical activities in France. Our results highlighted that contamination by different types of metals (mainly Cu and Pb) has led to an alteration in the production of secondary metabolites in the roots, stems and leaves of the hyper-accumulating Pteris vittata and for roots, a similar trend in the metabolic changes could be observed in another type of pollution context (Zn and Pb more particularly). Similarly, the metabolic profiles of the underground parts (roots and rhizomes) of Miscanthus x giganteus were modified by the concentrations of Pb, Cd and Zn in agricultural soils. For the two plants examined chlorogenic acid derivatives have been found in increased proportions in the roots despite soil type and pollution context were highly contrasted. However, catechic tannin derivatives are specifically found in higher proportions in the roots of P. vittata under metal pressure. These polyphenols are known for their ability to scavenge free radicals and their antioxidant properties and thus could be involved in the adaptation of these plants to metallic stress by helping to limit the oxidative stress generated by MTE. At the level of the aerial parts, we studied only the change for P. vittata and evidenced higher proportions of flavonoid derivatives for contaminated plants. Our metagenomic results allow us to conclude also on the effect of MTE on the diversity and the specific richness of the bacterial communities of the studied soils: a high contamination of Cu (10 times the allowed limit) decreased dramatically bacterial richness and diversity, while for more moderate MTE levels including Cu Pb and Zn, the diversity of rhizosphere bacterial communities was more explained by plant or season effect rather than an effect of MTE. This effect on P.vittata rhizosphere bacterial composition is reflected by an enrichment in genera known as opportunistic human pathogens, including Ralstonia, Acinetobacter, Burkholderia and Mycobacterium. In addition, Cupriavidus, known as a highly resistant genus, is the only P. vittata specifically associated genus found in increased proportions at both mining sites compared to non-contaminated rhizosphere soils. This genus could then be involved in the adaptation process of this plant with metal stress. As for the rhizospheric communities of Miscanthus x giganteus, the selection of Stenotrophomonas and Pseudomonas in agricultural soils contaminated with MTE was observed. As a part of this thesis, we have also developed a rapid method for testing the impact of plant metabolites on pathogenic strains of clinical and environmental origin and their efflux pump inhibition (EPI) activity of RND family. Our data thus showed interesting and notable EPI activities comparable to that of the efflux pump inhibitor PAßN for tested compounds issued from Fallopia x bohemica roots or for their derivatives
Janakiraman, Vani. „Réponse immunitaire innée et adaptative pour des motifs moléculaire associés aux mycobactéries pathogènes (« PAMPs »)“. Paris 6, 2010. http://www.theses.fr/2010PA066291.
Der volle Inhalt der QuelleMazurier, Mélanie. „Biodiversité et adaptation au pathogène racinaire Verticillium alfalfae chez Medicago truncatula : Importance de la micro-évolution“. Thesis, Toulouse 3, 2018. http://www.theses.fr/2018TOU30057/document.
Der volle Inhalt der QuellePathogens, animals and weeds are responsible for losses ranging from 20% to 40% of global agricultural yield. Legumes are the second most grown crops after cereals as human and animal food, and their yield is also affected by pathogens. Verticillium alfalfae is a soil-borne pathogen causing high yield losses in alfalfa fields (Medicago sativa), the most worldwide legume forage crop grown. To date, there is no chemical control and crop breeding is the best way to protect alfalfa against V. alfalfae. However, Medicago sativa has a complex genome (allogamous and tetraploid), therefore in this work the model legume Medicago truncatula (diploid and self-fertile) was used to investigate genetic mechanisms involved in V. alfalfae V31-2 (Va V31-2) resistance. First, several sources of resistance were identified in M. truncatula biodiversity by assessing disease symptoms development in 261 lines from the Mediterranean basin inoculated by V. alfalfae V31-2. Reisolation of V. alfalfae V31-2 in M. truncatula stems was also led. These analyses revealed a great biodiversity of M. truncatula response towards Va V31-2. A genome wide association study (GWAS) on various disease phenotypes pinpointed several quantitative trait loci (QTL): one of them colocalized with a previous major QTL on chromosome 7 detected on LR4 and LR5 RILs populations. Both phenotypic and genetic analyses thus suggest the occurrence of different resistance mechanisms in M. truncatula populations towards V. alfalfae. Resistant candidate genes towards Va V31-2 were also identified by GWAS using 90 accessions of M. truncatula Soliman Tunisian population. These candidate genes are different from the pinpointed candidate gene of our previous GWAS analysis. These results might underline a local adaptation towards Verticillium. Consistencies between GWAS results with previous QTL and transcriptomic data led us to perform the functional validation with the candidate genes localized on chromosome 7. An original in vitro inoculation system of M. truncatula transgenic roots was used to validate Medtr7g070480 (gene encoding a SEC14 protein) as a key player towards V. alfalfae V31.2 in M. truncatula. Silencing the SEC14 gene using artificial microRNA in A17 (resistant) and F83005.5 (susceptible) lines decreases Va V31-2 colonization rate on transgenic roots whereas overexpressing MtSEC14 increases the colonization rate in A17. This MtSEC14 gene appears as a disease susceptibility gene. Moreover, 18.5% of the disease variation in the studied M. truncatula accessions is explained by the unique non-synonymous polymorphism between A17 and F83005.5 in MtSEC14. Root expression patterns of the SEC14 gene one day after inoculation by Va V31-2 was also analyzed in response to inoculation among a panel of 14 susceptible and resistant M. truncatula accessions of diverse geographic origins. No significant differences were found. At the same time, orthologous resistance candidate genes towards Va V31.2 in several other model species (Lotus japonicus, Arabidopsis thaliana, Nicotiana sp.) were discovered. Pathogenicity of Va V31-2 in these species was monitored to use them as potential model for functional validation. Only one orthologous gene of MtSEC14 has been identified in Medicago sativa. Because of a great synteny between M. truncatula and M. sativa, our work could be useful for alfalfa breeding. In this work and for the first time, a susceptibility gene involved in a quantitative resistance against microorganisms in Legumes was identified
Pandiani, Franck. „Mécanismes d’adaptation aux basses températures de croissance de la bactérie pathogène B. cereus : rôle des hélicases à ARN“. Thesis, Avignon, 2010. http://www.theses.fr/2010AVIG0634/document.
Der volle Inhalt der QuelleBacillus cereus is a widespread bacteria, thus contaminating all raw materials in contact with soil. In France, B. cereus is considered as the fourth causative agent of foodborne illness. To be pathogenic, B. cereus should multiply during the various stages of food processing and particularly during preservation at low temperature. The aim of this study was to study molecular mechanisms of the adaptive response at low temperature and more precisely the involvement of the B. cereus ATCC 14579 RNA helicases. The cshA gene encoding a putative RNA helicase was identified by a random mutagenesis approach, as playing a major role in cold adaptation of B. cereus. The ATCC 14579 strain possesses 5 genes encoding putative RNA helicases, cshA to cshE, which were all strongly overexpressed at 10°C versus 37°C, whatever the growth stage. The simple deletion of cshA, cshB, and cshC lead to a cold-sensitive phenotype, resulting in an inability to adapt at 10 °C compared to the wild type strain, associated to a huge modification of cell morphology. In addition, CshA, CshB and CshC have a temperature range where their action is decisive. The role of these three RNA helicases also appears to be important in adaptation to oxidative and basic stresses while CshD and E did not appear to be involved in the adaptation to the tested stresses. The RNA helicase CshA has the most important role in adaptation to cold. We demonstrated that CshA is essential at low temperature to allow the maintenance of ribosome stability. CshA interacts directly with ribosomes, and also regulate rRNA degradation. The identification of protein partners that interact with CshA suggests that it could be involve in a complex of RNA decay
Poulicard, Nils. „Emergence et adaptation du Rice yellow mottle virus : relations entre histoire évolutive, contournement de résistance et interactions hôte/pathogène“. Thesis, Montpellier 2, 2010. http://www.theses.fr/2010MON20121.
Der volle Inhalt der QuelleThe Rice yellow mottle virus (RYMV) is an emerging virus currently considered as the major constraint to rice production in Africa. Some varieties of African and Asian cultivated rice (Oryza glaberrima and O. sativa, respectively), have recently been identified as highly resistant to RYMV. This resistance phenotype is caused by a recessive gene RYMV1 encoding the translation initiation factor eIF(iso)4G1 of rice.The objectives of this thesis are (i) to investigate the durability of the high resistance of rice against RYMV before broadly deployment in fields, (ii) to characterize the mechanisms of emergence of resistance-breaking (RB) genotypes and (iii) to identify molecular signatures that influence these processes of adaptation. The resistance-breaking of two resistance alleles, identified in both cultivated rice species, is mainly associated with the emergence of mutations in the viral protein VPg that restore in resistant hosts the interaction with the factor eIF(iso)4G1. A site of VPg under diversifying selection directly affects the ability to overcome the high resistance depending on the host species. This site, near the RB mutations, is involved in the adaptation of the RYMV to O. glaberrima species during its evolutionary history. The approach used during this work combines experimental evolution and functional analyses. The results of this integrative study will participate in the development of effective and sustainable control strategies toward the Rice yellow mottle virus in Africa
Diomande, Sara Esther. „Adaptation au froid de la bactérie pathogène Bacillus cereus : étude de mécanismes impliqués et exploitation de la diversité génétique“. Thesis, Avignon, 2014. http://www.theses.fr/2014AVIG0666/document.
Der volle Inhalt der QuelleBacillus cereus sensu stricto (ss) is a major foodborne pathogen representing the second cause of foodpoisoning in France in 2012. This species belongs to Bacillus cereus sensu lato (sl) consisting of ubiquitousspecies genetically close-related and including other pathogens such as B. anthracis, B. thuringiensis and B.cytotoxicus. The strains of B. cereus sl are divided into seven phylogenetic groups with various growthtemperature ranges and characterized by three main thermotypes: thermotolerant, mesophilic,psychrotolerant. The B. cereus ss cold adaptation is a key mechanism because it determines B. cereusability to grow in refrigerated foods and achieve doses that can be dangerous to consumers. The aim of thisstudy was to study the molecular mechanisms involved in the cold adaptation of strains representing B.cereus sl diversity.We demonstrated that the genes encoding the two component system CasK/R are overexpressed at lowtemperature. CasK/R was found to be a generic mechanism for B. cereus sl cold adaptation as its role washighlighted in the study of four strains with different thermotypes and their respective isogenic mutantsΔcasK/R. A transcriptomic study on a B. cereus ATCC 14579 strain and its ΔcasK/R mutant strain revealedthat sixteen of the genes differentially expressed in both early log phase and stationary phase at lowtemperature encode proteins involved in the fatty acids metabolism. We showed the role of CasK/R in themodification of the membrane fatty acid composition via an increase of the proportion of unsaturated fattyacids during growth of B. cereus at low temperature. Furthermore, the gene encoding the desaturase DesA,mainly responsible of the fatty acids unsaturation at a low temperature is upregulated by CasK/R at lowtemperature.We also demonstrated that casK/R genes were organized in operon with a gene encoding a RpiR-likeregulator. Interstingly,, this operon is negatively regulated by CasK/R at low temperature in the stationaryphase. The individual rpiR promoter is repressed by CasK/R at low temperature but also optimal growthtemperature, suggesting also a role for CasK/R at optimal temperature
Richard, Damien. „Microévolution et adaptation à une pression de sélection anthropique chez Xanthomonas citri pv. citri, une bactérie pathogène des agrumes : dynamique du compartiment plasmidique“. Thesis, La Réunion, 2019. http://www.theses.fr/2019LARE0001.
Der volle Inhalt der QuelleCopper, frequently used in agriculture to control bacterial diseases, is commonly used against Xanthomonas citri pv. citri (Xcc), the bacterial agent of Asiatic citrus canker. The recent detection of a copper-resistant phenotype in two French overseas regions motivated a genomic study which revealed, in copper-resistant (CuR) strains, a conjugative plasmid encoding an adaptive transposon of the Tn3 family. Its conservation in several Xanthomonas species suggested the role of horizontal gene transfer (HGT) in Xcc adaptation. We therefore analyzed the evolutionary history of susceptible and CuR Xcc strains in the Indian Ocean using both SNP and gene content variations. The dating of the obtained phylogeny allowed us to hypothesize the history of Xcc introduction into the region. The phylogeny showed a strong geographic structure among islands of the Indian Ocean region, which faded at the Réunion scale and disappeared at the grove scale. Among the groves, admixture is a factor favoring HGT between genetically distinct strains. This form of evolution is however largely uncharacterized in the Xanthomonas genus. To fill this gap, we searched genetic homology between the whole known plasmid gene content of the Xanthomonadaceae family and the complete set of genomes hosted in NCBI databases. We highlighted both the ubiquity of plasmid genes in the Xanthomonadaceae family and the taxonomical barrier of their sharing by conjugation. The small fraction of genes that were exchanged through the complete sharing of plasmids also revealed the importance of plasmid mosaicism, partly due to mobile genetic elements. Taken together, our results highlight the importance of bacterial communities in the evolution of phytopathogenic bacteria of the Xanthomonas genus, and the need for a precise characterization of the content and the functioning of the Xanthomonadaceae environmental genome in order to fully apprehend the adaptation of these phytopathogenic bacteria
Jallet, Arthur. „Effet de la sélection fluctuante sur le pathogène du blé Zymoseptoria tritici par une approche d'évolution expérimentale“. Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLS349.
Der volle Inhalt der QuelleAn important challenge in Biology is to understand how organisms adapt to fluctuating environments and to determine the relative significance of phenotypic plasticity and mutations in this adaptation. We examined the response of a wheat pathogen (Zymoseptoria tritici) to temperature fluctuations using transcriptomics, phenotyping (relative fitness and disease level) and genomics. With this goal, we conducted an in vitro experimental evolution from two Z. tritici clones that evolved in three thermal conditions: at 17°C, at 23°C and under temperature fluctuations. Expression level of 11% of the genome evolved in a different way between the two founder genotypes that evolved under fluctuating conditions. We also observed a higher density of differentially expressed genes in regions known to be enriched in transposable elements. Evolution under fluctuating selection promoted robustness of the transcriptome. The relative fitness estimated in the same conditions as for the experimental evolution did increase for fluctuating lineages only for one of the founder genotypes. The difference of growth between the two ancestors in fluctuating conditions and their distinct level of expression plasticity could explain these opposite results. Finally we observed: i). in planta pathogenicity losses for lineages evolved at 17°C or under fluctuations ii). no accessory chromosome loss, iii). many de novo mutations, including coding mutations in effector genes. This work contributes to shade light on the evolutionary and molecular mechanisms underlying the evolution of Z. tritici in variable environments
Joubert, Aymeric. „Adaptation d'Alternaria brassicicola à son hôte : étude de composantes moléculaires impliquées dans la protection du champignon pathogène vis-à-vis des phytoalexines indoliques des Brassicaceae“. Angers, 2011. https://tel.archives-ouvertes.fr/tel-01143830.
Der volle Inhalt der QuelleAlternaria brassicicola is a nectrotrophic fungal pathogen responsible for the black spot disease of Brassicaceae that causes major damages in fields. During host infection, A. Brassicicola is exposed to high levels of defence compounds, such as the indolic phytoalexins called camalexin and brassinin. Previous studies showed that these compounds probably cause damage to fungal membranes and activate a compensatory mechanism in fungal cells aimed at preserving membrane integrity. The aim of this thesis consists in investigating the molecular basis of this mechanism. The results show that the unfolded protein response (UPR) and two MAPK signalling pathways, the cell wall integrity (CWI) and the high osmolarity glycerol (HOG) were activated in A. Brassicicola in response to phytoalexin exposure. Mutant strains lacking functional MAP kinases or AbHacA, the major UPR transcription regulator, showed in vitro hypersusceptibility to camalexin and brassinin. Replacement mutants exhibited a loss or an attenuation of the virulence on host plants that may partially result from their inability to cope with defence metabolites such a indolic phytoalexins. This study constitutes the first evidence that a phytoalexin activates fungal MAP kinases and UPR, and that outputs of activated pathways contribute to protecting the fungus against antimicrobial plant metabolites. A functional model of fungal signalling pathways regulated by camalexin is proposed and leads to consider new promising strategies for disease control
Andanson, Audrey. „Evolution de l'agressivité des champignons phytopathogènes, couplage des approches théorique et empirique“. Thesis, Nancy 1, 2010. http://www.theses.fr/2010NAN10094/document.
Der volle Inhalt der QuelleLiving organisms extract resources from their environment and invest them toward various biological functions (growth, survival, reproduction). Available resources in an environment are usually limited so that organisms have to trade-off the resources invested in different biological functions. These trade-offs in resource investment reverberate in trade-offs between life-history traits (age and size at maturity, number of offspring) and determine pathogen potential to adapt to their environment.During this work, we have studied resource allocation strategy during infection caused by spore-producing pathogen. We have determined optimal resource allocation strategies between intra-host multiplication and spore production in different ecological settings. The main result of this work is that the optimal strategy is defined by the existence of a latent period, a period of time during which all extracted resources are investing toward within-host multiplication and no spore is produced. After latency, when the pathogen has a limited access to host resources, consumed resources are invested toward spore production only (Bang-bang strategy). On the contrary, when the pathogen has an unlimited access to host resources, a fixed proportion of host resources are invested toward maintenance of within-host multiplication forms (Bang-mixte strategy). A second part of this work presents empirical test of these theoretical assumptions, through experimentations on Magnaporthe oryzae and on Melampsora larici-populina. Our observations on these pathogens seem to agree with our theoretical predictions and corroborate the relevance of our modelling assumptions and approach
Montarry, Josselin. „Réponse adaptative des populations de Phytophthora infestans, agent du mildiou de la pomme de terre, au déploiement en culture de son hôte Solanum tuberosum“. Rennes, Agrocampus, 2007. http://www.theses.fr/2007NSARC090.
Der volle Inhalt der QuelleUnderstanding the consequences of selection pressure by host plants on pathogen population structures in crucial for the effective management of durable resistance to plant diseases. The objectives of this work werre i) to assess the impact of selection on the phénotypic and genotypic structure of the local pathogen population of Phytophthora infestans, the causal agent of poptato late blight, as exerted by hosts with various levels of resistance ; ii) to determine if recurent selection pressure applied by prevalent cultivars in different potato production areas led to local adapatation of P. Infestans populations ; and iii) to test the hypothesis of a trade-off between aggressiveness during the epidemic phase of the disease and the over-winter survival capacity in clonal P. Infestans populations. Our results showed that selection by ost applies on both qualitative (virulence) and quantitative (aggressiveness) components of pathogenicity. The large variation in aggressiveness allowed adaptation of P. Infestants populations, which led to the erosion of partial resistance. French P. Infestants populations proved to be adapted to the cultivar prevalent nationally (Bintje), but not to locally prevalent cultivars. Local adpatation takes place in this system, but was detectable only on a very large spatial scale, for populations isolated geographically. Our results also showed that during winter survival there was no counter-selection fo the most aggressive strains by over-mortality of infected tubers. This work highlights the importance of considering all the evoutionary forces in order to describe and understand the adaptative response of pathogen populations. In the future modelling of demogenetic processes will allow the development and validation of effective strategies for resistance management
Pandiani, Franck. „Mécanismes d'adaptation aux basses températures de croissance de la bactérie pathogène B. cereus : rôle des hélicases à ARN“. Phd thesis, Université d'Avignon, 2010. http://tel.archives-ouvertes.fr/tel-00765823.
Der volle Inhalt der QuelleRipoll, Julie. „Effets de la contrainte hydrique, seule ou en interaction avec un pathogène, sur le fonctionnement de la plante et la qualité du fruit de Solanum lycopersicum L., en fonction du génotype“. Thesis, Avignon, 2015. http://www.theses.fr/2015AVIG0670/document.
Der volle Inhalt der QuelleIn horticulture, yield losses associated to water deficit (WD) could be compensated by positive effects on fruit quality and stimulation of plant to others stresses. The aim of the thesis was to explore a number of questions to assess the positive and negative effects of the WD, and to understand factors variations after setting a current knowledge of the effects of WD quality fruit. The questions were: 1) to characterize the effects of WD applied at specific stages of development of plant or fruit, 2) to understand the stress memory effect by alternating period of WD and recovery, 3) to test the stimulation of plant defences by WD during an infection by a pathogen, and 4) to study the genetic variability associated with responses to WD through the previous objectives. For this, several experiments were conducted in greenhouses and growth chambers. The parents of the MAGIC population of tomato (with rich allelic variability) were studied, as well as two commercial tomatoes (for the study of the interaction between WD and Botrytis cinerea). Plant response mechanisms induced during a WD were characterized in both plant vegetative and reproductive stages, and then during the fruit development stages (cell division, cell expansion and maturation). The plant vegetative and reproductive stages are distinguished by different mechanisms of oxidative stress management generated by WD. Vegetative plants are more affected at the photosystem II while reproductive plants rather modulate their water needs and responses at the photosystem I. The impact of WD on fruit quality differs according to fruit developmental stages. Strong genotypes effects were observed with an important increase in fruit taste quality (according to the concentrations in sugars and acids) for one genotype, which had poorer initial fruit quality than the second. Alternating periods of WD and recovery is a good compromise between water saving and plant adaptation (through proper management of oxidative stress). This alternation of stress has neutral to positive effects on fruit sugar content according to the genotypes and highly variable responses for contents of organic acids, carotenoids and ascorbic acid according to the genotypes. The interaction between a WD and B. cinerea generates a decrease of C/N ratio that can be associated to a stimulation of the pool of plant defence. However, the interaction between B. Cinerea and this WD promote pathogen development in stems. This deleterious effect of interaction seems attributable to hormonal regulation with the stimulation of the ABA pathway (by WD) and the SA pathway (by B. cinerea), which are antagonistic to the JA / ET pathway involved in response to necrotroph pathogens. However, a positive effect was observed for infections in detached leaves of infected plants, detached leaves represent a snapshot of plant defences and these results raise new questions. Overall, these data provide that WD improve fruit taste (sugars and acids) without yield losses but had variables effects on health promoting compounds. WD could permit the stimulation of plant defence but more research is needed. To finish, the genetic variability induced important variability in plant and fruit responses and interact with WD
Lê, Van Amandine. „Potentiel évolutif du pouvoir pathogène de Venturia inaequalis en lien avec la domestication du pommier et l'utilisation de résistances quantitatives en amélioration variétale“. Phd thesis, Université d'Angers, 2011. http://tel.archives-ouvertes.fr/tel-00663827.
Der volle Inhalt der QuelleMontarry, Josselin. „Réponse adaptative des populations de Phytophthora infestans, agent du mildiou de la pomme de terre, au déploiement en culture de son hôte Solanum tuberosum“. Phd thesis, Agrocampus - Ecole nationale supérieure d'agronomie de rennes, 2007. http://tel.archives-ouvertes.fr/tel-00133363.
Der volle Inhalt der QuelleLaurent, Benoit. „Base génétique et potentiel d’évolution de la pathogénicité de Fusarium graminearum, bio-agresseur fongique des céréales“. Thesis, Bordeaux, 2016. http://www.theses.fr/2016BORD0317/document.
Der volle Inhalt der QuelleF. graminearum is one of the main causal agents of the fusarium head-blight (FHB), a cereal disease leading to head necrosis, in addition to grain and food/feed contamination by stable and toxic metabolites. Recent observations refer to an increase of pathogenicity, questioning efficiency and durability of current management practices. In order to anticipate this evolution, we must bring a deeper characterization of the currently existing diversity. Six new genomes of F. graminearum were sequenced, and 243,000 genetic variations have been identified and characterized. Seventy seven percent of the total number of the variants was located within 32% of the genome, delineating highly polymorphic islands. These islands are enriched with probable effectors linked to Fusarium’s pathogenicity. The construction and the genotyping on 1,300 molecular markers of a recombinant population have enabled the development of the first high-density genetic map of the species. The remarkable correlation between polymorphism and recombination rate highlighted the 'two-speed' genome organization of this pathogen. Finally, the integration of these data through a quantitative genetic approach allowed the discovery of one quantitative trait locus, likely to affect the gene FgVeA, and responsible for 90% of the observed variation of aggressiveness and mycotoxin production. These results are discussed in the light of F. graminearum’s adaptive potential and evolution
Gopalan, Nair Rekha. „Déterminants moléculaires de l'adaptation à l'hôte chez la bactérie phytopathogène Ralstonia solanacearum“. Thesis, Toulouse 3, 2020. http://www.theses.fr/2020TOU30207.
Der volle Inhalt der QuelleThe Ralstonia solanacearum species complex (RSSC) is a destructive plant pathogen that infects more than 250-plant species including tomato, potato, pelargonium, ginger and banana. In addition, this multihost pathogen is known for rapid adaptation to new plant species and new environments. In order to overcome this pathogen, it is important to understand the molecular mechanisms that govern host adaptation. The objectives of this thesis were (1) to decipher the genetic bases of adaptation of a RSSC strain to a resistant cultivar, (2) to investigate the potential role of epigenetic modifications in host adaptation and (3) to analyze to impact of the plant species on genetic, transcriptomic and epigenetic modifications in RSSC adapted clones. This study was conducted on clones generated by experimental evolution of GMI1000 RSSC strain after 300 generation of serial passages on the resistant tomato ‘Hawaii 7996’ plant, the susceptible eggplant ‘Zebrina’ and the tolerant plant Bean ‘Blanc precoce’. Competitive experiments with the GMI1000 ancestral clone demonstrated that 95% of the clones evolved on Hawaii 7996 were better adapted to the growth into this tomato plant than the ancestral clone. Genomic sequence analysis of these adapted clones found between 0 and 2 mutations per clone and we demonstrated that they were adaptive mutations. Transcriptome analysis of the Hawaii, Zebrina and Bean evolved clones revealed a convergence towards a global rewiring of the virulence regulatory network as evidenced by largely overlapping gene expression profiles. Two transcription regulators, HrpB, the activator of the type 3 secretion system regulon and EfpR, a global regulator of virulence and metabolic functions, emerged as key nodes of this regulatory network that were frequently targeted by either genetic or potential epigenetic modification affecting their expression. Significant transcriptomic variations were also detected in evolved clones showing no mutation, suggesting a potential role of epigenetic modifications in adaptation. Comparison of the DNA methylation profiles between the evolved clones and the ancestral clone revealed between 13 and 35 differentially methylated regions (DMRs). No impact of the host plant on the list of DMRs appeared. Some of these DMRs targeted genes that were identified to be differentially expressed between the evolved clones and the ancestral clone. This result supported the hypothesis that epigenetic modifications regulate gene expression and could play a major role in RSSC adaptation to new host plants
De, La Garza García Jorge. „Réponse de Brucella microti et Brucella suis au stress acide à pH 4.5 : Approches transcriptomiques et génétiques“. Thesis, Montpellier, 2020. http://www.theses.fr/2020MONTT067.
Der volle Inhalt der QuelleAdaptation of Brucella microti and Brucella suis to acid stress at pH 4.5: Transcriptomic and genetic approachesThe atypical new species Brucella microti, isolated from wild animals and a very close relative of the classical zoonotic species Brucella suis bv. 1 1330, is fast growing and lethal in mice. Both species represent an appropriate model for classical/atypical Brucella spp. comparisons. Despite highly conserved genome sequences with over 99 % identity, these species are phenotypically distinct from one another and developed species-specific responses to acid stress. The more acid-resistant phenotype of B. microti may have major implications in fitness and virulence, influencing bacterial survival in soil and in host.Here, we propose to identify and characterize the acid resistance determinants of both species by an in vitro comparative RNAseq-based transcriptome analysis in minimal medium at pH 4.5 and 7.0. A total of 1376 significantly regulated genes were selected. The expression rate of 106 genes was individually assessed by RT-qPCR, yielding an average validation score of 70 %. 19 acid stress-regulated genes were mutagenized (deleted or overexpressed) in B. microti and/or B. suis and the phenotypes of 31 mutant strains were analyzed for their ability to survive under acid conditions at pH 4.5 and in the murine J774 macrophage infection model.The study revealed a ”core” acid stress response with 651 genes regulated in both species, including higher expression, among others, of genes encoding the F1F0-ATPase components, cytochromes (cco and cyd), the respiratory complex I, the main histidine metabolic pathways (his and hut operons), and the urease system. B. suis, more acid-sensitive, specifically regulated a set of 284 genes, with increased expression of genes coding for diverse heat shock proteins and also nucleic acid-, peptidoglycan-, and LPS synthesis-related genes, indicating the set-up of defense and repair mechanisms essential for structural integrity of the bacteria. In contrast, the species-specific acid stress response of B. microti was more pronounced, regulating 441 genes and displaying different particularities, including the strong activation of genes encoding all steps of the denitrification pathway, participating in iron and sulfur metabolism, and of genes classified as pseudogenes in B. suis, but potentially functional in B. microti.In-depth analysis of genes of interest allowed the identification of two factors directly responsible for the increased long-term acid resistance of B. microti: The cold shock protein CspA (pseudogene in B. suis) and the "DNA-binding protein from starved cells" Dps, a nucleoid-associated protein. In contrast, inactivation of any of the selected genes did not affect intramacrophagic survival of the mutants, notably during acidification of the early Brucella-containing vacuole. The acid resistance-related roles of CspA and Dps confirmed our initial hypothesis, postulating that the marked phenotypical divergence between B. suis and B. microti, existing despite highly conserved genome sequences, was due to point mutations and / or to differential gene expression.This study presents a first thorough, comparative analysis of global transcriptional regulation during acid stress responses of a classical and an atypical Brucella spp. The results obtained contribute to a better understanding of species-specific phenotypes and provide solid evidences that may open new avenues for further investigations on the adaptation of Brucella spp. to acid environments
Schmitt, Paulina. „Diversité moléculaire des effecteurs antimicrobiens chez l'huître creuse Crassostrea gigas : mise en évidence et rôle dans la réponse antimicrobienne“. Thesis, Montpellier 2, 2010. http://www.theses.fr/2010MON20158/document.
Der volle Inhalt der QuelleThis work contributed to the knowledge of the molecular bases of oyster immunity by the characterization of the diversity of three antimicrobials of C. gigas and the understanding of the role played by their diversity in the oyster antimicrobial response. Phylogenetic analyses of two antimicrobial peptides (AMPs), Cg-Defensins (Cg-Defs) and Cg-Proline rich peptide (Cg-Prp), and one Bactericidal Permeability Increasing protein, Cg-BPI, led us to the identification of a high diversity for both AMPs. Further analyses showed that this diversity is generated by gene duplication, allelic recombination and directional selection pressures, suggesting their functional diversification. The biological meaning of AMP diversity was investigated for the three major variants of Cg-Defs, which revealed a strong but variable potency against Gram-positive bacteria. We evidenced that oyster defensins kill S. aureus through binding to the cell wall precursor lipid II, resulting in the inhibition of peptidoglycan biosynthesis. Finally, transcript expression and localization of oyster antimicrobials after a pathogenic infection evidenced a complex network in their expression profiles in hemocyte populations and oyster tissues, suggesting a potential interplay between antimicrobials as a result of their colocalization. Indeed, the combination of oyster antimicrobials produced strong synergistic activities that enlarged their antimicrobial spectra. Thus, the diversity of oyster antimicrobials may provide significant means in acquiring functional divergence, probably concerned in the evolutionary arms race between hosts and their pathogens.From our data, it would provide oysters with a higher protection against the potential pathogens from their environment
Go, Natacha. „Modélisation de la réponse immunitaire au virus du Syndrome Dysgénésique et Respiratoire Porcin“. Thesis, Paris, AgroParisTech, 2014. http://www.theses.fr/2014AGPT0070/document.
Der volle Inhalt der QuellePRRSv is responsible for significant worldwide production losses and its control is a major challenge for the swine industry. Vaccination, the main control measure, does not allow to eradicate the infection and only confers a partial protection to the host. This lack of efficiency is mainly due to the strong variability in PRRSv strain virulence, which induces highly variable within-host dynamics. This thesis aims at better understanding the interactions between the virus and the immune response in order to improve PRRSv control. To tackle this issue, a dynamic and deterministic modelling approach was chosen. We developed an original immunological model consisting in an integrative representation of the within-host dynamics. It describes the immune mechanisms at the between-cell scale, including the innate response, the activation and orientation of the adaptive response and their complex regulations by the major cytokines. Our first results show that similar infection durations associated with contrasted immune dynamics are explained by the consideration of the immune mechanisms affected by the strain virulence. They provide new insights to explain apparent inconsistencies between experimental data. We then showed that the exposure, whose effect is often neglected, has an impact on the within-host dynamics, which varies depending on the virulence level. Finally, the within-host dynamics induced by the infection of a vaccinated pig was explored, providing new insights to improve vaccine efficiency. This thesis also provides new insights to guide further experimental and modelling approaches and promising prospects for PRRSv control at the herd level