Ce manuscrit présente des études expérimentales sur l'évaporation de gouttes et la chimiotaxie de la mite.Une première partie s'intéresse à l'évaporation de spray dense au moyen d'une nouvelle approche, par analogie avec le mélange scalaire. Dans cette limite de forte densité en gouttes, où il y a saturation en vapeur au sein des structures constituantes, l'évaporation est principalement fonction de l'étirement auxquelles ces structures sont soumises. C'est en effet celui-ci qui conditionne le taux d'évacuation de cette vapeur interstitielle, ce qui permet de mettre les gouttes en contact avec un environnement plus sec, déclenchant ainsi leurs évaporations.Une deuxième partie s'intéresse à une application de la compréhension de cette dynamique d'évaporation de spray dense à un contexte d'entomologie: la chimiotaxie de la mite. Il s'agit du processus par lequel l'animal va se repérer dans un champ de concentration, pour localiser la source d'une substance attractive par exemple (ici de la phéromone sexuelle). Cette partie a tendu vers l'obtention d'une visualisation conjointe de la trajectoire de l'animal et du champ de concentration sous-jacent par la visualisation des gouttes. / This thesis present some experiments on droplets evaporation and moth chemotaxis.In a first part, dense spray evaporation is explained through a new approach, drawing an analogy with scalar mixing. In this high density droplets limit, where vapor saturation is reached within the structures, evaporation is mainly controlled by the intensity at which these structures are stretch. It is indeed the stretching that controls the rate at witch interstitial vapor is evacuated: droplets are thus in contact with a dryer environment, so they can start to evaporate.A second part take an interest in applying dense spray evaporation dynamic understanding to an entomologist situation: moth chemotaxis. This is the process by which animals find their way in a concentration field, such at finding a chemoattractant source for instance (sexual pheromone in our case). This part tended towards visualizing animal trajectory and concentration field underlying through droplets visualization simultaneously.

Bacterial motility, and in particular repulsion or attraction towards specific chemicals, has been a subject of investigation for over 100 years, resulting in detailed understanding of bacterial chemotaxis and the corresponding sensory network in many bacterial species including Escherichia coli. E. Coli swims by rotating a bundle of flagellar filaments, each powered by an individual rotary motor located in the cell membrane. When all motors rotate counter-clockwise (CCW), a stable bundle forms and propels the cell forward. When one or more motors switch to clock-wise (CW) rotation, their respective filaments fall out of the bundle, leading to the cell changing orientation. Upon switching back to CCW, the bundle reforms and propels the cell in a new direction. Chemotaxis is performed by the bacterium through prolonging runs by suppressing CW rotation when moving towards nutrients and facilitating reorientation by increasing CW bias when close to a source of a harmful substance. Chemicals are sensed through interaction with membrane bound chemosensors. These proteins can interact with a very specific set of chemicals and the concentrations they are able to sense are in the range between 10-⁶ and 10-² M. However, experiments have shown that the osmotic pressure exerted by large (> 10-¹ M) concentrations of solutes, which have no specificity for binding to chemosensors (e.g. sucrose), is able to send a signal down the chemotactic network. Additionally, clearing of bacterial density away from sources of high osmolarity has been previously observed in experiments with agar plates. This behaviour has been termed osmotaxis. The aim of this doctoral thesis work is to understand how different environmental cues influence the tactic response and ultimately, combine at the network output to direct bacterial swimming. As tactic responses to chemical stimuli have been extensively studied, I focus purely on the response to non-specific osmotic stimuli, using sucrose to elevate osmolarity. I monitor the chemotactic network output, the rotation of a single bacterial flagellar motor, using Back Focal Plane Interferometry over a variety of osmotic conditions. Additionally, in collaboration with Vincent Martinez, I studied the effect of elevated osmolality on swimming speed of large (104) bacterial populations, using differential dynamic microscopy (DDM). I have found that sudden increases in media osmolarity lead to changes of both motor speed and motor clockwise bias, which is the fraction of time it spends rotating clockwise. Changes in CW Bias proceed in two phases. Initially, after elevating the osmolarity, CW Bias drops to zero, indicating that the motor is exclusively in the ‘cell run’ mode. This phase lasts from 2-5 minutes depending on the magnitude of the change in solute concentration. What follows then is a distinct second phase where the CW Bias is elevated with respect to the initial levels and this phase lasts longer than 15-20 minutes. In comparison, for defined chemical stimuli, the motor output resets after several seconds, a behaviour termed perfect adaptation. For changes of 100 mOsm/kg and 200 mOsm/kg in magnitude the motors speed up, often by as much as a factor of two, before experiencing a gradual slow down. Despite the slow down, motors still rotate faster 15-20 minutes after the change in osmolarity, than they did before. For changes of 400 mOsm/Kg in magnitude the motors decrease sharply in speed, coming to a near halt, recovering after 5 minutes and eventually, on average, speeding up. DDM studies of free swimming bacteria have shown that elevated osmolality leads to higher swimming speeds, in agreement with single motor data. Using theoretical models of bacterial swimming from the literature, it is discussed how this motor output, although different to what is expected for chemotaxis, is able to drive bacteria away from regions of space with high osmolalities. Additionally, I have started extending the work done with sucrose, to another solute often used to elevate osmolality, sodium chloride. While sucrose is outer membrane impermeable, NaCl can cross the outer membrane into the periplasmic space. Another layer of complexity is that NaCl has some specificty for the chemoreceptors. The preliminary results are shown and qualitatively agree with those obtain with sucrose.

Bacteria swim towards improving conditions by controlling flagellar activity via signals (CheY) sent from chemosensory protein clusters, which respond to changing stimuli. The best studied chemotactic bacterium, E. coli, has one transmembrane chemosensory protein cluster controlling flagellar behaviour. R. sphaeroides has two clusters, one transmembrane and one cytoplasmic. The roles of the two clusters in regulating swimming and chemosensory behaviour are explored here. Newly-developed software was used to measure the effect of deleting or mutating each chemotaxis protein on unstimulated swimming and on the chemosensory response to dynamic change. New behaviours were identified by using much larger sample sizes than previous studies. R. sphaeroides chemotaxis mutants were classified as (i) stoppy unresponsive; (ii) smooth unresponsive or (iii) stoppy inhibited compared to wildtype swimming and chemosensory behaviour. The data showed that the ability to stop during free-swimming is not necessarily connected to the ability to respond to a chemotaxis challenge. The data suggested a new model of connectivity between the two chemosensory pathways. CheY₃ and CheY₄ are phosphorylated by the transmembrane polar cluster in response to external chemoeffector concentrations. CheY₆-P produced by the cytoplasmic cluster is a requirement for chemotaxis, whether or not the polar cluster is able to produce CheY₆-P. CheY₆-P stops the motor, whereas CheY_3,4-P allow smooth swimming. When chemoeffector levels fall, the signals through CheY_3,4 fall, allowing CheY₆-P to bind and stop the motor. As the polar cluster adapts to the fall by the action of the adaptation proteins CheB₁ and CheR₂, the concentration of CheY_3,4-P increases again, to compete with CheY₆-P and allow periods of smooth swimming. Under aerobic conditions, the cytoplasmic cluster controls the basal stopping frequency and does not appear to respond to external chemoeffector changes. The role of the adaptation proteins in resetting the signalling state in R. sphaeroides is unclear, particularly the roles of the proteins associated with the cytoplasmic cluster, CheB₂ and CheR₃. Tandem mass spectrometry was used to identify glutamate and glutamine (EQ) sites on the cytoplasmic R. sphaeroides chemoreceptor TlpT that are deamidated and methylated by the R. sphaeroides adaptation homologues. In E. coli, adaptation sites are usually EQ/EQ pairs. However the sites reported in TlpT vary at the first residue in the pair. Mutation of the putative EQ adaptation sites caused changes in adaptation, suggesting that CheY₆-P levels are controlled and reset by CheB₂ and CheR₃ controlling the adaptation state of TlpT.

abstract: Presented is a study on the chemotaxis reaction process and its relation with flow topology. The effect of coherent structures in turbulent flows is characterized by studying nutrient uptake and the advantage that is received from motile bacteria over other non-motile bacteria. Variability is found to be dependent on the initial location of scalar impurity and can be tied to Lagrangian coherent structures through recent advances in the identification of finite-time transport barriers. Advantage is relatively small for initial nutrient found within high stretching regions of the flow, and nutrient within elliptic structures provide the greatest advantage for motile species. How the flow field and the relevant flow topology lead to such a relation is analyzed. / Dissertation/Thesis / Masters Thesis Mathematics 2015

Ticks are blood feeding parasites that secrete a number of immunomodulatory factors to evade host immune response. The aim of this study was to prepare a tick salivary protein with anti-chemokine activity and to observe the influence of salivary gland extrakt on neutrophile´s chemotaxis.

Orientador: Fernando Ferreira Costa / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Ciencias Medicas / Made available in DSpace on 2018-08-13T14:17:07Z (GMT). No. of bitstreams: 1 Bezerra_MarcosAndreCavalcanti_D.pdf: 919225 bytes, checksum: 5524005c5d425fe7e16e9c36cfd7275b (MD5) Previous issue date: 2009 / Resumo: O estado inflamatório crônico que ocorre na doença falciforme (DF) é decorrente de diversos fatores que se interligam e se retroalimentam, formando um ciclo inflamatório permanente. Estudos prévios sobre as propriedades adesivas e funcionais das células são restritos à forma homozigota do gene da HbS (SS). No entanto, trabalhos que avaliem essas características celulares, que possam contribuir para o esclarecimento da heterogeneidade clínica em outros grupos de DF e talassemia intermediária (TI), são escassos na literatura. O objetivo desse trabalho foi avaliar a capacidade adesiva de células vermelhas, neutrófilos e plaquetas, quimiotaxia dos neutrófilos, os níveis plasmáticos das citocinas inflamatórias e o stress oxidativo na DF e ß-TI. Dessa maneira foram selecionados pacientes com DF: SS (n=20), SC (n=20), 3 grupos com S/ß talassemia - S/ß-IVS-I-6 (T->C) (n=17), S/ß-IVS-I-5 (G->C) (n=16), S/ß-Códon39 (C??T) (n=12) - e TI homozigotos para a mutação IVS-I-6 (T->C) (n=20), acompanhados na Fundação HEMOPE. As técnicas utilizadas no desenvolvimento desse estudo foram: ensaio de quimiotaxia (ChemoTx) para avaliação da capacidade migratória dos neutrófilos, adesão estática para determinação da adesão basal das células, citometria de fluxo para avaliar a produção de ROS e a expressão de moléculas de adesão, e ELISA para determinar a atividade da superóxido dismutase (SOD) e a dosagem das citocinas. Para avaliação de nossos resultados, todos os grupos de pacientes foram comparados ao grupo controle AA: a adesão de neutrófilos e plaquetas mostrou-se significativamente aumentada em todos dos grupos de DF; somente os grupos SS e SC apresentaram capacidade quimiotática significativamente aumentada, assim como a adesão de células vermelhas e a expressão das moléculas de adesão CD36 e CD49d. Os níveis plasmáticos das citocinas IL1-ß, IL-6, IL-8 e TNF-a mostraram-se significativamente aumentados no grupo SS, e nos demais grupos de DF apresentaram uma distribuição heterogênea. Observamos um aumento significativo na produção de ROS em células vermelhas, mononucleares e neutrófilos de todos os grupos de DF, exceto para os grupos S/ß nas células vermelhas. Além disso, a atividade plasmática da SOD mostrou-se reduzida nos grupos SS, SC e S/ß-Cd39. A adesão dos neutrófilos, células vermelhas e plaquetas foi significativamente maior nos pacientes com TI, assim como a expressão das moléculas CD36 e CD49d nas células vermelhas e a capacidade quimiotática dos neutrófilos. Nesses pacientes, a produção de ROS e os níveis plasmáticos das citocinas foram significativamente aumentados, enquanto que a atividade enzimática da SOD foi significativamente reduzida. Apesar da doença SC possuir uma clínica mais branda, nossos dados sugerem que neutrófilos, glóbulos vermelhos e plaquetas desses pacientes possuem características adesivas e quimiotáticas semelhantes às encontradas nas células de pacientes com AF. Além disso, nossos resultados sugerem que quanto maiores os níveis de HbA na S/ß talassemia, menor a adesão de neutrófilos, células vermelhas e plaquetas, podendo explicar as diferenças clínicas encontradas nesses pacientes em função do genótipo. É possível que o aumento da aderência, da capacidade quimiotática, da produção de ROS, das citocinas e diminuição do mecanismo antioxidante, observados neste estudo, contribuam nas complicações clínicas encontradas na ß-TI, tais como hipertensão pulmonar e úlceras de perna. Estudos adicionais podem contribuir para o entendimento das diferenças na apresentação clínica desses pacientes. / Abstract: The chronic inflammatory state that occurs in sickle cell disease (SCD) is due to several factors that are interlinked and feeds back to a permanent inflammatory cycle. Previous studies about the adhesive properties and functional cells are restricted to the homozygous form of the HbS gene (SS). However, studies that assess the cellular characteristics that may contribute to the clarification of clinical heterogeneity in other groups of SCD and thalassemia intermedia (TI), are scarce in the literature. The aim of this study was to evaluate the adhesive properties of red blood cells (RBC), platelets and neutrophils (NS), NS chemotaxis, inflammatory cytokine plasma levels and oxidative stress in SCD and ß-TI patients. Thus, we selected patients with different SCD genotypes: SS (n=20), SC (n=20), three groups of HbS/ß thalassemia - HbS/ß39 (C->T) (n=12), HbS/IVSI- 5 (G->C) (n=16), and HbS/IVS-I-6 (T->C) (n=17) - and patients with homozygous thalassemia intermedia IVS-I-6 (T->C) - followed regularly at the Fundação HEMOPE - Brazil. The techniques used in the development of this study were: chemotaxis assay (ChemoTx) to evaluate the migratory ability of neutrophils, basal adhesion was compared using static adhesion assays, flow cytometry to assess the production of ROS and expression of adhesion molecules, and ELISA to determine the superoxide dismutase (SOD) activity and cytokine plasma levels. For evaluation of our results, all groups of patients were compared with the AA control group: the neutrophil and platelet adhesions were significantly increased in all groups of SCD, only the SS and SC groups showed significant increase in the chemotactic ability, as well as the RBC adhesion and the expression of adhesion molecules CD36 and CD49d. All the SCD groups investigated showed an increase in IL-6 plasma levels. IL1-ß levels were significantly higher in the S/ß-IVS-I-5 (G??C), S/ß-Cd39 and SS groups. Plasma levels of IL-8 were increased only in the SS and SC groups, however TNF-a levels were significantly higher in SS and the three groups with HbS-ß thalassemia. NS and mononuclear cell ROS production was significantly increased in all SCD groups, however red blood ROS production was higher only in the SS and SC groups. Moreover, the SOD plasma activity was shown to be reduced in groups SS, SC and S/ß-Cd39. The NS, RBC and platelets adhesion was significantly higher in TI patients, as well as the expression of molecules CD36 and CD49d in RBC and chemotactic ability of NS. In these patients, the ROS production and cytokines plasma levels were significantly increased, while SOD plasma activity was significantly reduced. Although SC disease has a milder clinical manifestations, our data suggest that NS, RBC and platelets of these patients have chemotactic and adhesive characteristics similar to those found in cells of patients with SS. Moreover, our results suggest that the higher levels of HbA in S/ß thalassemia reduce the NS, RBC and platelets adhesion and may explain the clinical differences found in these patients, according to genotype. It is possible that the increase in the cell adherence, chemotactic capacity, ROS production, of cytokines levels and the reduction in antioxidant mechanism, observed in this study, contribute to several clinical complications of ß-TI, such as pulmonary hypertension and leg ulcers. Further studies may contribute to our understanding of the differences in the clinical presentation of these patients. / Doutorado / Medicina Experimental / Doutor em Fisiopatologia Medica

Em sentido geral, a quimiotaxia é o movimento dirigido que desenvolvem alguns seres vivos em resposta aos gradientes químicos presentes no seu ambiente. Uma bactéria é um organismo unicelular que usa a quimiotaxia como mecanismo de mobilização para encontrar os nutrientes de que precisa para sobreviver e para escapar de ambientes nocivos. Evoluída durante milhões de anos pela natureza, a quimiotaxia de bactérias é um processo altamente otimizado de busca e exploração em espaços desconhecidos. Graças aos avanços no campo da computação, as estratégias quimiotácticas das bactérias e sua excelente capacidade de busca podem ser modeladas, simuladas e emuladas para desenvolver métodos de otimização inspirados na natureza que sejam uma alternativa aos métodos já existentes. Neste trabalho, desenvolvem-se dois algoritmos baseados em estratégias quimiotácticas de bactérias: o BCBTOA (Bacterial Chemotaxis Based Topology Optimization Algorithm) e o BCMOA (Bacterial Chemotaxis Multiobjective Optimization Algorithm) os quais são um algoritmo de otimização topológica e um algoritmo de otimização multi-objetivo, respectivamente. O desempenho dos algoritmos é avaliado mediante a sua aplicação à solução de diversos problemas de prova e os resultados são comparados com os de outros algoritmos atualmente relevantes. O algoritmo de otimização multi-objetivo desenvolvido, também foi aplicado na solução de três problemas de otimização de projeto mecânico de eixos. Os resultados obtidos e os analise comparativos feitos, permitem concluir que os algoritmos desenvolvidos são altamente competitivos e demonstram o potencial do processo de quimiotaxia de bactérias como fonte de inspiração de algoritmos de otimização distribuída, contribuindo assim, a dar resposta à constante demanda por técnicas de otimização mais eficazes e robustas. / In general, chemotaxis is the biased movement developed by certain living organisms as a response to chemical gradients present in their environment. A bacterium is a unicellular organism that uses chemotaxis as a mechanism for mobilization that allows it to find nutrients needed to survive and to escape from harmful environments. Millions of years of natural evolution became bacterial chemotaxis a highly optimized process in searching and exploration of unknown spaces. Thanks to advances in the computing field, bacterial chemotactical strategies and its excellent ability in searching can be modeled, simulated and emulated developing bio-inspired optimization methods as alternatives to classical methods. Two algorithms based on bacterial chemotactical strategies were designed, developed and implemented in this work: i) the topology optimization algorithm, BCBTOA (Bacterial Chemotaxis Based Topology Optimization Algorithm) and ii) the multi-objective optimization algorithm, BCMOA (Bacterial Chemotaxis Multiobjective Optimization Algorithm). Algorithms performances were evaluated by their applications in the solution of benchmark problems and the results obtained were compared with other algorithms also relevant today. The BCMOA developed here was also applied in the solution of three mechanical design problems. The results obtained as well as the comparative analysis conducted lead to conclude that the algorithms developed were competitive. This also demonstrates the potential of bacterial chemotaxis as a process in which distributed optimization techniques can be inspired.

Les bactéries sont capables de percevoir leur environnement et de s’y adapter grâce aux systèmes Che dont les récepteurs nommés MCPs (Methyl-accepting Chemotaxis Proteins) détectent des signaux transduits jusqu’à un régulateur de réponse qui agit sur différentes cibles pour conduire à une réponse cellulaire adaptée. Le génome de Myxococcus xanthus code pour huit opérons définissant huit systèmes Che putatifs et 13 mcp « orphelins » codés ailleurs dans le génome. Une combinaison de trois approches : de phylogénétique ; de localisation des MCPs et d’interaction protéine-protéine a révélé la présence d’un large module chimiotactique composé de trois systèmes Che et six MCPs. Nous avons aussi montré que tous ces modules ont un rôle clé dans la régulation de la motilité et du cycle développemental chez M. xanthus.L’étude des déterminants de la localisation du système Frz a ensuite montré que pour la première fois le MCP forme des foyers uniquement suite à sa liaison directe au nucléoide. Une analyse à haut débit des foyers Frz suggère que cette liaison au nucléoide permet aussi une ségrégation correcte des complexes Frz durant la division cellulaire. Ainsi comme chez E. coli la membrane sert de support pour la formation des foyers Che transmembranaires, notre modèle est que l’ADN lui-même qui servirait de support pour la formation de foyers cytoplasmiques Frz chez M. xanthus. Ce travail a donc mis en évidence une diversification des systèmes Che et une organisation encore jamais observée. Nous avons ainsi montré que l’ADN peut aussi être utilisé afin d’organiser, de structurer et de ségréger des complexes cytoplasmiques tels que les systèmes Che. / Bacteria are able to perceive their environment and adapt thanks to Che systems with receptors named MCPs (Methyl-accepting chemotaxis Proteins) detecting signals transduced to a response regulator which acts on different targets leading to an appropriate cellular response.Myxococcus xanthus genome encodes eight putative operons defining eight Che systems and 13 "orphans" mcp encoded elsewhere in the genome. A combination of three approaches: phylogenetic; MCPs localizations and protein-protein interactions have revealed the presence of a large chemotactic module composed of three Che systems and six MCPs. We have also shown that these MCPs have key roles in the regulation of the motility and the developmental cycle and in M. xanthus.The study of the determinants of the Frz system localization has shown that for the first time the MCP forms clusters only after its direct binding to the nucleoid. A high-throughput analysis of Frz clusters suggests that this nucleoid binding also allows a correct segregation of Frz complexes during cell division. As well as in E. coli membrane serves as support for the clustering of Che transmembrane systems, our model is that the nucleoid itself serves as a support for the formation of cytoplasmic Frz clusters in M. xanthus.This work has highlighted a diversification of Che systems and a new organization never observed. We have also shown that DNA can be used to organize, to structure and to segregate cytoplasmic complexes such as Che systems.

Experiments were performed to assess the suitability of Rhabditis pellio, a nematode found in earthworms, as a challenge organism for use in development of a biomarker assay to determine the potential of chemicals to suppress the immunocompetence of the non-specific immune system. To accomplish this goal, information on the life cycle of R. pellio was determined; including effects of incubation time and temperature on growth rates; along with information on the immune response elicited in the earthworm, Lumbricus terrestris. Immune parameters measured were coelomocyte migration toward and attachment to R. pellio larvae and adults. Preliminary background information showed that R. pellio has potential as a challenge organism for development of a biomarker assay.

Orientador: Carlos Lenz Cesar / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-08-08T01:06:24Z (GMT). No. of bitstreams: 1 Pozzo_LilianadeYsasa_M.pdf: 4076293 bytes, checksum: 5197fda41d6fa440de56b82b104a4bcd (MD5) Previous issue date: 2006 / Resumo: Microorganismos unicelulares, como os demais seres vivos, necessitam interagir com o ambiente e procurar ativamente por alimentos. Seus orgãos sensoriais, entretanto, se limitam a sensores hidrodinâmicos e receptores bioquímicos de membrana. A quimiotaxia estuda a resposta de organismos unicelulares frente a gradientes de concentração de substâncias atratoras ou repulsoras. Essa resposta é parte essencial do processo de infecção por parasitas no direcionamento e reconhecimento das células a serem infectadas. Dessa forma, um estudo quantitativo da quimiotaxia de parasitas requer o monitoramento tanto dos movimentos do parasita quanto das intensidades, direção e sentido das forças que exerce na presença de gradientes de concentração das substâncias atratoras e repulsoras. Forças de microorganismos com dimensões da ordem de 10 µm são da ordem de pico-Newtons. A pinça óptica é a microferramenta ideal para esse tipo de estudo pelas seguintes razões: (1) tem sensibilidade para medir forças desde 20 femto-Newtons até 200 pico-Newtons, da mesma ordem de grandezas das forças geradas pelos parasitas; (2) é uma técnica remota, sem necessidade de contacto e (3) não destrutiva, pois os lasers no infravermelho não geram calor suficiente para causar danos térmicos. Nesse trabalho mostramos como se pode utilizar o deslocamento da posição de equilíbrio de uma microesfera como transdutor de forças vetoriais, determinando quantitativamente intensidade, direção e sentido das forças na microesfera. Um detector de quadrante da luz do próprio laser da pinça óptica fornece o deslocamento da mesma em duas dimensões. Dessa forma foi possível monitorar a força exercida pelo parasita em tempo real em diferentes gradientes de concentração de várias substâncias. Também desenvolvemos uma câmera de gradiente que garantiu um gradiente unidimensional estacionário na qual se pode aprisionar os parasitas e realizar a medida vetorial da força em função do tempo. Demonstramos a capacidade do nosso sistema de realização de medidas de quimiotaxia utilizando o protozoário Leishmania amazonensis, responsável pela doença leishmaniose, na forma promastigota, na presença de gradientes de glucose. Nossos resultados mostram que além das forças serem fortemente direcionadas na direção do gradiente, que a intensidade das mesmas diminui nas direções contrária ou perpendicular ao gradiente. Com esse trabalho mostramos a construção de um sistema de medidas quantitativa capaz de estudar quantitativamente a quimiotaxia de qualquer parasita frente a qualquer gradiente de concentração de diferentes substâncias / Abstract: Unicellular microorganisms, like others live beings, need to interact with environment to find nourishment. They have only hydrodynamics sensors and biochemical receptors on membrane to accomplish this task. The response of the microorganism to concentration gradients of attractive or repulsive chemical substances is called chemotaxis. The investigation of chemotaxis is essential to understand infection processes and how parasites recognizes and directs itself to the cells to be infected. This way a quantitative study of parasites chemotaxis requires the observation of not only its movements, but also the strength, direction and sense of forces exerted in the presence of concentration gradient of attractive or repellent chemical substances. Microorganism¿s forces with dimensions of around 10µm are the order of pico-Newton. Optical tweezers are a suitable tool for this kind of investigation, we can justify this affirmation by the following reasons: (1) it has high sensibility to measure forces from 20 femto-Newton until 200 pico-Newton. These forces are in same order of the forces exerted by the parasites. (2) This technique does not need contact, therefore it is a remote technique; and (3) this tool does not destroy the parasites, because lasers on infrared band do not generate enough heat to cause thermal damage on them. In this work we used the displacements of a microsphere trapped in an Optical Tweezers as the force transducer to measure the direction and the strength of the propulsion forces of flagellum of the microorganism under several gradient conditions. A quadrant detector was utilized to sense the displacement of optical tweeter¿s laser in two dimensions. So we monitor the force exerted by the parasites in real time in several concentrations gradients of different substances. We also developed a system enable to create concentration gradient. This system guaranteed a stationary one-dimensional gradient, which the parasites were arrested and the vectorial measurements of force in time function were realized. In this study, we used the protozoa Leishmania amazonensis in its promastigote form. It is responsible by the disease called leishmaniose and it represents a serious problem of public health. We demonstrated that our system is able to perform chemotaxis measurements in gradients of glucose. Our results suggest that the direction and strength of force can be used to identify the movement of the parasite. We also notice differences in strength forces for both direction x and y for different glucose in several concentrations. Using that system we can investigate quantitatively taxias of any parasites in any concentration gradient with different chemical substance, temperature or other variables / Mestrado / Física / Mestre em Física