This dissertation thesis focuses on the removability of algal organic matter (AOM) by coagulation during water treatment and also on the influence of AOM on the coagulation of other substances present in source water. Special emphasis is put on the description of coagulation mechanisms. The effectiveness of AOM removal by coagulation was investigated by coagulation tests performed with optimized doses of coagulants (aluminium or ferric sulphate) under different pH values. Peptides and proteins contained in cellular organic matter of cyanobacterium Microcystis aeruginosa were used in the experiments since they have been previously reported to disturb the coagulation process. Moreover, peptides and proteins underwent coagulation experiments together with kaolin particles, representing clay particles in turbid waters, in both the presence and absence of coagulants to investigate the effect of AOM on the coagulation of turbid waters. To enable the description of coagulation mechanisms, AOM were characterised in terms of charge, functional groups, molecular weight and ability to form dissolved complexes with coagulant metals. The experimental results demonstrated that the removability of peptides and proteins is greatly dependent on pH value and on the properties of the involved particles or molecules....

Microcistinas são potentes hepatotoxinas e promotoras de tumores encontradas em águas doces que causam riscos à saúde pública e, portanto, representam um sério problema para as estações de tratamento de água. O gênero de cianobactéria Microcystis é o mais conhecido produtor dessas toxinas e também o mais comumente encontrado formando florações em reservatórios de água usados para abastecimento público. Entretanto, algumas bactérias são capazes de utilizar essas toxinas como fonte de carbono o que pode contribuir para a sua remoção da água. Neste estudo foi avaliado o potencial de degradação da microcistina-XR (MCYST-XR) por bactérias heterotróficas isoladas de um sistema de abastecimento público de água da cidade de Piracicaba-SP. A cianotoxina MCYST-XR avaliada foi isolada da linhagem Microcystis aeruginosa NPLJ-4 e purificada. Culturas puras de 35 bactérias isoladas do sistema de abastecimento de água foram testadas. Para isso, cada bactéria foi inoculada em meio mínimo de sais contendo 60 g mL-1 de MCYST-XR purificada e após 144 horas a degradação da toxina foi avaliada por análise em LC-MS/MS. Os picos indicando a massa da microcistina-XR (m/z 1037) não foram detectados no meio de cultura de seis bactérias, as quais foram identificadas pelo sequenciamento quase completo do gene de RNAr 16S como pertencentes aos gêneros Pseudomonas sp., Sphingomonas sp., Microbacterium sp., Agromyces sp., Bacillus sp. e Acinetobacter sp. Este é o primeiro relato de uma linhagem de Acinetobacter capaz de degradar MCYST. A cinética de biodegradação da MCYST-XR mostrou redução de 80% em 72 horas, período em que as bactérias apresentaram o máximo crescimento. A presença do gene mlrA codificante da enzima microcistinase envolvida no metabolismo da microcistina foi avaliada nos genomas dos seis isolados bacterianos usando iniciadores de PCR específicos. Fragmentos de aproximadamente 800 pb foram amplificados em dois isolados, Bacillus sp.e Microbacterium sp. Ensaios de toxicidade utilizando o cládocero Daphnia similis foram realizados para verificar a efetiva remoção da MCYST-XR e a não formação de subprodutos tóxicos na via de biodegradacão. Os resultados negativos dos bioensaios após 48 horas indicaram a ausência de subprodutos tóxicos na via da degradação. / Microcystins are potent hepatotoxins and tumor promoters found in freshwaters that cause public health risks and thus represent a serious problem for water treatment plants. The cyanobacterium genus Microcystis is the most known toxin-producer and the most common bloom-forming in water reservoirs used for public supply. However, some bacteria are able to use these toxins as carbon source, which can contribute to its removal from water. This study assessed the potential for degradation of microcystin-XR (MCYST-XR) by heterotrophic bacteria isolated from a public water supply system of the city of Piracicaba-SP. The cyanotoxin MCYSTXR evaluated was isolated from Microcystis aeruginosa strain NPLJ-4 and purified. Pure cultures of 35 bacteria isolated from the water supply system were tested. For this, each bacterium was inoculated in minimal medium salts containing 60 g mL-1 of purified MCYST-XR and after 144 hours the toxin degradation was evaluated by LC-MS/MS analysis. The peaks indicating the mass of microcystin-XR (m/z 1037) were not detected in the culture medium of six bacteria, which were identified by almost complete sequencing of the 16S rRNA gene as belonging to the genera Pseudomonas sp., Sphingomonas sp., Microbacterium sp., Agromyces sp., Bacillus sp. and Acinetobacter sp. This is the first report of an Acinetobacter strain able to degrade MCYST. The kinetic of the MCYST-XR biodegration showed 80% reduction in 72 hours, period in which the bacteria showed the maximum growth. The presence of the mlrA gene encoding the microcystinase enzyme involved in the metabolism of microcystin was evaluated in the genomes of the six bacterial isolates using specific PCR primers. Fragments of approximately 800 bp were amplified in two isolates, Bacillus sp. and Microbacterium sp. Toxicity assays using the cladoceran Daphnia similis were conducted to verify the effective removal of MCYST-XR and the non formation of toxic by-products in the biodegradation pathway. The negative results of the bioassays after 48 hours indicated absence of toxic by-products in the biodegradation pathway.

Microcistinas são potentes hepatotoxinas e promotoras de tumores encontradas em águas doces que causam riscos à saúde pública e, portanto, representam um sério problema para as estações de tratamento de água. O gênero de cianobactéria Microcystis é o mais conhecido produtor dessas toxinas e também o mais comumente encontrado formando florações em reservatórios de água usados para abastecimento público. Entretanto, algumas bactérias são capazes de utilizar essas toxinas como fonte de carbono o que pode contribuir para a sua remoção da água. Neste estudo foi avaliado o potencial de degradação da microcistina-XR (MCYST-XR) por bactérias heterotróficas isoladas de um sistema de abastecimento público de água da cidade de Piracicaba-SP. A cianotoxina MCYST-XR avaliada foi isolada da linhagem Microcystis aeruginosa NPLJ-4 e purificada. Culturas puras de 35 bactérias isoladas do sistema de abastecimento de água foram testadas. Para isso, cada bactéria foi inoculada em meio mínimo de sais contendo 60 g mL-1 de MCYST-XR purificada e após 144 horas a degradação da toxina foi avaliada por análise em LC-MS/MS. Os picos indicando a massa da microcistina-XR (m/z 1037) não foram detectados no meio de cultura de seis bactérias, as quais foram identificadas pelo sequenciamento quase completo do gene de RNAr 16S como pertencentes aos gêneros Pseudomonas sp., Sphingomonas sp., Microbacterium sp., Agromyces sp., Bacillus sp. e Acinetobacter sp. Este é o primeiro relato de uma linhagem de Acinetobacter capaz de degradar MCYST. A cinética de biodegradação da MCYST-XR mostrou redução de 80% em 72 horas, período em que as bactérias apresentaram o máximo crescimento. A presença do gene mlrA codificante da enzima microcistinase envolvida no metabolismo da microcistina foi avaliada nos genomas dos seis isolados bacterianos usando iniciadores de PCR específicos. Fragmentos de aproximadamente 800 pb foram amplificados em dois isolados, Bacillus sp.e Microbacterium sp. Ensaios de toxicidade utilizando o cládocero Daphnia similis foram realizados para verificar a efetiva remoção da MCYST-XR e a não formação de subprodutos tóxicos na via de biodegradacão. Os resultados negativos dos bioensaios após 48 horas indicaram a ausência de subprodutos tóxicos na via da degradação. / Microcystins are potent hepatotoxins and tumor promoters found in freshwaters that cause public health risks and thus represent a serious problem for water treatment plants. The cyanobacterium genus Microcystis is the most known toxin-producer and the most common bloom-forming in water reservoirs used for public supply. However, some bacteria are able to use these toxins as carbon source, which can contribute to its removal from water. This study assessed the potential for degradation of microcystin-XR (MCYST-XR) by heterotrophic bacteria isolated from a public water supply system of the city of Piracicaba-SP. The cyanotoxin MCYSTXR evaluated was isolated from Microcystis aeruginosa strain NPLJ-4 and purified. Pure cultures of 35 bacteria isolated from the water supply system were tested. For this, each bacterium was inoculated in minimal medium salts containing 60 g mL-1 of purified MCYST-XR and after 144 hours the toxin degradation was evaluated by LC-MS/MS analysis. The peaks indicating the mass of microcystin-XR (m/z 1037) were not detected in the culture medium of six bacteria, which were identified by almost complete sequencing of the 16S rRNA gene as belonging to the genera Pseudomonas sp., Sphingomonas sp., Microbacterium sp., Agromyces sp., Bacillus sp. and Acinetobacter sp. This is the first report of an Acinetobacter strain able to degrade MCYST. The kinetic of the MCYST-XR biodegration showed 80% reduction in 72 hours, period in which the bacteria showed the maximum growth. The presence of the mlrA gene encoding the microcystinase enzyme involved in the metabolism of microcystin was evaluated in the genomes of the six bacterial isolates using specific PCR primers. Fragments of approximately 800 bp were amplified in two isolates, Bacillus sp. and Microbacterium sp. Toxicity assays using the cladoceran Daphnia similis were conducted to verify the effective removal of MCYST-XR and the non formation of toxic by-products in the biodegradation pathway. The negative results of the bioassays after 48 hours indicated absence of toxic by-products in the biodegradation pathway.

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Submitted by Edisangela Bastos (edisangela@ufpa.br) on 2013-04-08T21:47:49Z No. of bitstreams: 2 license_rdf: 23898 bytes, checksum: e363e809996cf46ada20da1accfcd9c7 (MD5) Dissertacao_AspectosClinicosEpidemiologicos.pdf: 52663750 bytes, checksum: ce81246a5e8618e2ca804bacd85f6d45 (MD5) / Approved for entry into archive by Ana Rosa Silva(arosa@ufpa.br) on 2013-04-09T13:08:18Z (GMT) No. of bitstreams: 2 license_rdf: 23898 bytes, checksum: e363e809996cf46ada20da1accfcd9c7 (MD5) Dissertacao_AspectosClinicosEpidemiologicos.pdf: 52663750 bytes, checksum: ce81246a5e8618e2ca804bacd85f6d45 (MD5) / Made available in DSpace on 2013-04-09T13:08:18Z (GMT). No. of bitstreams: 2 license_rdf: 23898 bytes, checksum: e363e809996cf46ada20da1accfcd9c7 (MD5) Dissertacao_AspectosClinicosEpidemiologicos.pdf: 52663750 bytes, checksum: ce81246a5e8618e2ca804bacd85f6d45 (MD5) Previous issue date: 2003 / Pseudomonas aeruginosa é um bacilo gram-negativo, importante patógeno para pacientes neutropênicos, queimados e em condições de ventilação artificial em Unidades de Tratamento Intensivo, onde causam infecção nosocomial. Nestas condições, a infecção pode ser séria e muitas vezes letal. Em pacientes com fibrose cística, o curso da patologia por P. aeruginosa evolui como uma infecção pulmonar crônica severa, pois a bactéria produz diversas toxinas e outros fatores de virulência responsáveis pelo estabelecimento da colonização persistente do trato respiratório destes pacientes. A apresentação característica da persistente infecção por P. aeruginosa é a produção de alginato mucóide e a formação de microcolônias, que é considerada a estratégia de sobrevivência da bactéria no meio ambiente, P. aeruginosa crescendo em biofilm é altamente resistente a antibióticos, estando usualmente associada com progressiva perda da função pulmonar. Esta pesquisa realizou uma avaliação epidemiológica e clínica de portadores de fibrose cística, colonizados por P. aeruginosa, atendidos no Hospital Universitário João de Barros Barreto, na cidade de Belém, Pará no ano de 2003. Foi feito coleta de escarro dos pacientes expectoradores e swab de orofaringe nos demais para estudo microbiológico realizado no laboratório microbiologia deste hospital. Foram avaliados 32 pacientes fibrocísticos, distribuídos em três grupos, conforme: ausência de infecção por P. aeruginosa (G1), infecção pela bactéria sem colonização (G2) e colonização crônica (G3). Pacientes pertencentes a G3 apresentaram complicações respiratórias mais frequëntes e mais graves que os demais. A ocorrência de cepas mucóidaes de P. aeruginosa foi significativamente mais prevalente neste grupo, onde a doença respiratória se apresentou de forma mais severa. Cepas não-mucóides foram identificadas de forma similar nos grupos G2 e G3. Os sintomas respiratórios foram os mais frequëntes ao diagnóstico. A idade média dos pacientes ao diagnóstico foi de 7 anos. Condições sócio-econômicas adversas, diagnóstico tardio, desnutrição e mutação genética parecem ter favorecido a colonização e contribuído para ocorrência de óbito no grupo G3. / Pseudomonas aeruginosa is a gram-negative motile rod; they are important pathogens in neutropenic patients, burn and artificially ventilated patients in Intensive Care Units, where they may cause nosocomial infections. At this condition, the infection seems to be serious and sometimes lethal. However, in Cystic Fibrosis patients the course of infection by P. aeruginosa, has become severe chronic lung infection, because this bacteria produce many toxins and others virulence factors with potential effect on the lungs of this patients that are thought to play a role during establishment of the initial persistent colonization of the Cystic Fibrosis respiratory tract. The most characteristic feature of persistent P. aeruginosa infection is the production of mucoid alginate and the formation of the micro colonies in the lungs of the patients that is the survival strategy of environrnent bacteria. P. aeruginosa growing in alginate biofilms is highly resistant to antibiotics and is usually associated with progressive loss of pulmonary function. This research wants to study Cystic Fibrosis patients chronically colonized by P. aeruginosa who has been taken care on University Hospital João de Barros Barreto, Belém (Pará), in 2003 year, at about epidemiological and clinicalaspects. The sputum of these patients, have been collected by expectoration and swab of throat, to microbiological study realized on microbiology laboratory of this hospital. Thirty two patients with Cystic Fibrosis have been evaluated and divided according microbiological aspect of their sputum in three groups: patients who have never been infected by P. aeruginosa (Gl), patients that have been infected by this bacterial but not colonized (G2), patients chronically colonized by this microorganism. Patients who concern to G3 group have been more serious respiratory complications than patients that belong to the others groups. The pattern mucoid of P. aeruginosa has been significant on patients' sputum of G3. The incident of non- mucoid strains in most patients of groups G2 and G3 seems to be similar. Respiratory symptoms have been important during diagnosis of Cystic Fibrosis. The median age for fibrosis cystic diagnosis was about 7,69 years. Certainly several events contribute to support P. aeruginosa respiratory colonization on Cystic Fibrosis patients of G3, like: low social and economic conditions, lateness diagnosis, malnutrition and pattern Cystic Fibrosis gene mutation.

Orientador: Pasqual Barretti / Resumo: Peritonite por bacilos Gram-negativos não fermentadores (BGNNF) é complicação importante da diálise peritoneal (DP), com curso clínico grave e elevada taxa de falência do método. Fatores associados à virulência, resistência antimicrobiana, formação de biofilme, entre outros, têm sido relatados, mas o limitado conjunto de evidências não permite concluir sobre os fatores responsáveis pelo pior curso clínico dessas infecções. O objetivo deste trabalho foi avaliar a influência das características microbiológicas, das condições clínicas do paciente e do tratamento na evolução de peritonites por BGNNF, ocorridas num único centro, em período de 18 anos. A sensibilidade in vitro aos antimicrobianos, produção de biofilme, além da análise do perfil clonal das bactérias pela técnica de eletroforese em gel de campo pulsado foram realizadas em todos os isolados bacterianos. Foram pesquisados genotipicamente, em isolados de Pseudomonas aeruginosa, a presença de marcadores de virulência (alginato, exoenzima S, fosfolipases C, exotoxina A, protesase alcalina, elastase e ramnolipídeos). Associações entre as características microbiológicas do paciente e tratamento com a taxa de resolução da peritonite foram estudadas. A espécie mais frequente foi Pseudomonas aeruginosa (45,59%), seguida por isolados do complexo Acinetobacter baumannii (17,65%). O estudo dos fatores de virulência da Pseudomonas aeruginosa revelou a presença de fatores de virulência em 100% dos casos, exceto exoenzima S (58,33%)... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Peritonitis due to non-fermentative Gram-negative bacilli (NFGNB) is a serious complication of peritoneal dialysis (PD), with a severe clinical course and high technique failure rate. Factors as bacterial virulence, antimicrobial resistance, biofilm formation, among others, have been reported, but the limited amount of evidence does not allow to conclude on the factors responsible for the worst clinical course of these infections. The objective of this study was to evaluate the influence of the microbiological characteristics, patients conditions, and treatment on evolution of peritonitis episodes at a single center in an 18 - year period. In vitro susceptibility, biofilm production, and clonal profile analysis of bacteria by pulsed-field gel electrophoresis (PFGE) were performed in all isolates. The presence of virulence markers (alginate, exoenzyme S, phospholipases C, exotoxin A, alkaline protease, elastase, and ramnolipids) was genotyped in bacterial isolates of Pseudomonas aeruginosa. From the data referring to the patient and causal agent, associations between the microbiological, patient characteristics, and treatment on the resolution rate of peritonitis were analyzed. The most frequent species was Pseudomonas aeruginosa (45.59%), followed by Acinetobacter baumannii complex (17.65%). The study of the virulence factors of Pseudomonas aeruginosa revealed the presence of virulence factors in 100% of the cases, except for exonzyme S (58.33%) and hemolytic phospholipase C ... (Complete abstract click electronic access below) / Mestre

Il polietilene (PE) rappresenta più del 60% di tutte le plastiche derivate dal petrolio a livello mondiale, e si sta accumulando ad un tasso di diversi milioni di tonnellate per anno a causa della sua riluttanza alla degradazione biotica e abiotica. La degradazione microbica è stata proposta come possibile strada alternativa nella riduzione dei rifiuti plastici. Lo scopo generale di questo lavoro è stata l'identificazione di ceppi batterici in grado di metabolizzare il PE e di identificare le vie metaboliche coinvolte in tale processo di biodegradazione. Abbiamo analizzato mediante approccio metagenomico diversi campioni di plastica raccolti in una discarica abbandonata, ed è stata scoperta una forte relazione tra le proprietà della plastica (inclusa la presenza di coloranti) e la comunità microbica Analizzando la comunità microbica esposta al PE nell’ ambiente, abbiamo isolato 10 ceppi batterici in grado di crescere utilizzando il PE come unica fonte di energia e di carbonio. Uno di questi ceppi, Pseudomonas aeruginosa UC4003, ha mostrato la più alta capacità di crescere in terreno minimo e polietilene. Quando cresce su PE, questo ceppo produce un enzima extracellulare, proteina-attivatore per l’ossidazione degli n-alcani (PA), coinvolto nelle prime fasi di degradazione di polietilene. / Plastics production, use and degradation are hot topics that have come to the forefront over recent years. Polyethylene (PE) represents more than 60% of all petroleum-derived plastics worldwide and is accumulating at rates of several millions of tons per year because of its strong recalcitrance to biotic and abiotic degradation. Microbial degradation has been proposed as a possible alternative way to reduce plastic wastes. The general aim of this work was the identification of bacterial strains able to metabolize PE and to identify the biochemical pathways of this biodegradation process. In an abandoned landfill we collected different plastic samples; using a metagenomic approach, we found a strong relationship between the plastic properties (including the presence of colorants) and the microbial community By screening the natural microbial community exposed to PE in environment, we isolated 10 bacteria which revealed the ability to grow on PE as only energy and carbon source. A bacterium, Pseudomonas aeruginosa UC4003, showed the highest growth rate in minimal salt medium and polyethylene. When grown on PE, this strain produced an extracellular enzyme, protein-like activator for n-alkane oxidation (PA), involved in the first step of polyethylene degradation.

Cyanobacterial blooms in lakes impact human health, the economy, and ecosystem health. It is predicted that climate change will promote and increase the frequency and intensity of cyanobacterial blooms due to unique physiological adaptions that allow cyanobacteria to exploit warm stable water bodies. Key cyanobacteria physiological adaptions include nitrogen fixation, buoyancy regulation and higher optimum growth temperatures. The largest uncertainty of predicting the effect of climate change is in understanding how the interactions among species will change. Adding to the ambiguity, cyanobacteria physiological adaptions can vary based on lakespecific ecotypes and can have different sensitivities to temperature. It is critical to understand how cyanobacterial physiological adaptions impact species interactions in order to improve and devise adaptable, short‐term management methods for bloom control. This study investigated how weather patterns and algal buoyancy regulation influence the competition and accumulation of two bloom‐forming buoyant cyanobacteria species (Aphanizomenon flos‐aquae (APFA) and toxin‐forming Microcystis aeruginosa (MSAE)) in Upper Klamath Lake (UKL), Oregon. The focus was confirming the buoyancy rate of the APFA in Upper Klamath Lake and exploring whether short‐term weather conditions could lead to dangerous accumulations of APFA or MSAE. A sensitivity analysis was conducted on the model's buoyancy terms and growth curves to see if the outcome of competition was influenced by these parameters. UKL specific buoyancy rates were measured on APFA from samples taken directly from the lake in the summer of 2015. Tracking software was used to measure APFA movement through water, and individual colony movement was averaged to obtain a single buoyancy rate. There was a high degree of agreement between the calculated APFA buoyancy rate in UKL (0.89 ± 0.34 m hr-1) with the rate published by Walsby (1995; 0.9 ± 0.5 m hr-1). This study investigated how weather patterns and buoyancy regulation influenced the outcome of competition between APFA and MSAE. Weather and water column temperature data were collected from UKL in the summer of 2016. A onedimensional hydrodynamic model was used to calculate the lake's thermal and turbulence structure on days with contrasting weather patterns (hot/cool and windy/calm). A competition model was used to calculate the accumulation of APFA and MSAE cells in regular intervals through the water column under the various weather scenarios. MSAE accumulation was significantly influenced by the thermal and turbulence regimes, but APFA maintained high accumulations under every regime and was the better competitor under every thermal and turbulence regime. MSAE was more negatively impacted by high turbulence than low temperatures. APFA's optimum temperature growth curve was found to be important in determining the outcome of competition between APFA and MSAE. Surprisingly, competition was not sensitive to changes in buoyancy rates. Buoyancy was not found to be a function of algal accumulation under any thermal and turbulence regime. The impacts of climate change and human‐induced enrichment has the potential to change existing patterns of species interactions in lentic systems. Restoration and management efforts should consider the significance of cascading ecological responses to climate change. Understanding how key physiological adaptions operate is the first step to assessing the scope of this impact. While buoyancy might not play a large role in competition in UKL, it might be possible to use mixing to suppress MSAE because it is negatively impacted by high turbulence. If MSAE hot spots become a reoccurring problem in UKL, lakes managers might be able to use localized mixing to suppress MSAE blooms in these problem areas.

Pseudomonas aeruginosa (PA) représente une des causes principales d'infections respiratoires acquises chez les patients aux défenses immunitaires altérées et la colonisation par PA est une étape marquante de la dégradation de la fonction pulmonaire chez les patients atteints de mucoviscidose. Le traitement de ces infections est difficile à cause de la résistance naturelle du pathogène à un grand nombre d'antibiotiques et d'une augmentation de la prévalence des souches ayant acquis une multi-résistance.<br />Les facteurs de virulence de PA induisent une augmentation des sécrétions apicale de fluide par l'activation des transports transépithéliaux ainsi qu'une perturbation de l'homéostasie calcique au niveau de l'épithélium respiratoire ; cependant l'impact de ces effets reste encore mal compris. <br />Sur un modèle de culture cellulaire de cellules épithéliales respiratoires en co-culture avec différentes souches de PA, nous montrons un effet protecteur d'un chélateur calcique (EGTA) sur la mort cellulaire induite par l'activation du système de sécrétion de type III (TTSS), un des principaux facteurs de virulence de PA. L'EGTA agit en diminuant l'adhésion de la bactérie et l'injection des exotoxines du TTSS dans le cytoplasme de la cellule épithéliale. Sur ce modèle, nous montrons aussi que les toxines du TTSS et l'EGTA induisent des modifications du cytosquelette des cellules épithéliales. L'autre partie de ce travail démontre le rôle du LPS de PA dans l'augmentation du calcium intracellulaire et la sécrétion de chlore des cellules épithéliales bronchiques humaines. Le LPS induit un relargage du calcium du réticulum ainsi qu'une entrée de calcium extracellulaire par des canaux membranaires. Cet effet est corrélé avec une augmentation de la sécrétion de chlore apicale dépendante de l'activation du CFTR mais aussi des canaux chlores activés par le calcium.<br />Ces effets rapides et encore peu décrits des facteurs de virulence de PA associés au rôle important du calcium intracellulaire et de la sécrétion de chlore des cellules épithéliales dans la signalisation de l'infection constituent probablement un des premiers signaux perçus par l'hôte. Ces mécanismes constituent une étape essentielle en recherche fondamentale afin de mieux appréhender les mécanismes physiopathologiques pour développer de nouvelles approches thérapeutiques en alternative aux antibiotiques.

La glycobiologie structurale est la branche de la biologie qui étudie la structure et les interactions de glucides, molécules jouant des rôles d'extrême importance dans tous les organismes. Dans la première partie de la thèse, nous nous sommes intéressés à la structure 3D de deux glycoconjugués, la tricolorine A et un O-glycanne de la protéine de Tamm-Horsfall, en utilisant les méthodes de cristallographie et de modélisation moléculaire. Le sujet développé dans la deuxième partie est centré sur l'interaction de glucides avec leurs récepteurs protéiques, les lectines. Les lectines sont une importante classe de protéines avec la capacité de “lire” l'information biologique qui est codifiée dans la structure 3D des sucres. La cristallographie macromoléculaire en combinaison avec des techniques de biophysique, telles que la microcalorimétrie de titration, ont été utilisées pour élucider les bases structurales et thermodynamiques de la reconnaissance lectine-sucre. Deux lectines, produites par les bactéries pathogènes opportunistes Pseudomonas aeruginosa et Chromobacterium violaceum et ayant un rôle dans l'infectivité, ont été étudiées. La structure tridimensionnelle de la lectine de Psathyrella velutina, le premier membre d'un nouvelle famille des lectines de champignon a également été résolue.