Submitted by (lucia.rodrigues@ufrpe.br) on 2017-03-24T15:08:49Z No. of bitstreams: 1 Myrzania de Lira Guerra.pdf: 1530658 bytes, checksum: 73ad27186e300f4bbcd6fd5b19977dd1 (MD5) / Made available in DSpace on 2017-03-24T15:08:49Z (GMT). No. of bitstreams: 1 Myrzania de Lira Guerra.pdf: 1530658 bytes, checksum: 73ad27186e300f4bbcd6fd5b19977dd1 (MD5) Previous issue date: 2015-07-24 / Xanthomonas campestris pv. viticola (Xcv) is the causal agent of grapevine bacterial canker. In the Submédio do Vale São Francisco in the northeast of Brazil, bacterial canker is one of the most important grapevine diseases, responsible for severe damage and representing a serious risk to Brazilian viticulture and wine production. The aims of this study were to: a) evaluate the ability of seven Xcv strains to adhere and form biofilms in vitro and to determine the influence of the culture medium and surfaces on biofilm formation, besides to study the biofilm architecture and swarming motility; and b) optimize a method of protein extraction for proteomic analysis of the Xcv, comparing the efficiency of four methods, based on the twodimensional gel electrophoresis profile (2D-PAGE). All the strains adhered to the wells of the polystyrene microtiter plate and formed biofilms in all liquid culture medium (nutrient brothdextrose- yeast extract, yeast extract-dextrose-calcium carbonate, KADO 523 and Luria-Bertani), though to different degrees (weak, moderate and strong). In glass tubes, only Xcv229 and Xcv158 strains formed biofilms. We identified Xcv229 as a strong biofilmproducing strain. Using confocal laser scanning microscopy (CLMS) only Xcv229 showed an initial matrix of biofilm structure after 24 h of growth. Scanning electron microscopy (SEM) images of strains Xcv229 and Xcv158 grown for 36 h on microtiter plates revealed typical biofilm architectures. Strain Xcv158 displayed a higher swarming motility than Xcv229, showing that in this case, biofilm formation is not motility-dependent. This is the first report of biofilm production by the bacterial plant pathogen Xcv. Trizol®, Phenol, Centrifugation and Lysis methods were tested and through quantitative and qualitative analysis, the most suitable method to obtain high-quality protein was selected. All methods enabled the extraction of a significant amount of proteins; nevertheless, the centrifugation method allowed obtaining the highest concentration of solubilized proteins. However, the analysis of the 2D-PAGE gel images revealed a larger number of spots in the lysis method when compared to the others. Taking into consideration the quality of the results and the practical advantages of the lysis method, this is recommended as the best option for total protein extraction of Xcv for proteomic studies. / Xanthomonas campestris pv. viticola (Xcv) é o agente causal do cancro bacteriano da videira. No Submédio do Vale São Francisco, no nordeste do Brasil, o cancro bacteriano é uma das doenças mais importantes dessa cultura, sendo responsável por grandes prejuízos, o que representa um sério risco para a viticultura brasileira. Os objetivos deste estudo foram: a) avaliar a capacidade de sete isolados de Xcv para aderir e formar biofilmes in vitro e determinar a influência do meio de cultura e das superfícies na formação de biofilme, além de investigar a arquitetura do biofilme e motilidade swarming; e b) otimizar um protocolo para extração de proteínas para análise da proteômica de Xcv, comparando a eficiência de quatro métodos com base no perfil de eletroforese em gel bidimensional (2D-PAGE). Todos os isolados aderiram aos poços da placa de microtitulação de poliestireno e formaram biofilmes nos meios de cultura líquidos testados (caldo nutriente-dextrose-extrato de levedura, extrato de levedura-dextrose-carbonato de cálcio, KADO 523 e Luria-Bertani), em níveis fraco, moderado e forte. Em tubos de vidro, apenas os isolados Xcv229 e Xcv158 formaram biofilmes. Xcv229 foi considerado um forte produtor de biofilme. Na microscopia confocal a laser (MCL) apenas em Xcv229 visualizou-se a matriz inicial da estrutura do biofilme, após 24 h de crescimento. As imagens da microscopia eletrônica de varredura (MEV) de Xcv229 e Xcv158 crescidos durante 36 h em placas de microtitulação revelaram arquiteturas típicas de biofilme. O isolado Xcv158 apresentou uma maior motilidade swarming do que Xcv229, mostrando que, neste caso, a formação de biofilme é independente da motilidade. Este é o primeiro relato de produção de biofilme bacteriano pela fitobactéria Xcv. Os métodos Trizol®, fenol, centrifugação e lise foram analizados quantitativa e qualitativamente, para selecionar o mais adequado na obtenção de proteína de alta qualidade. Todos permitiram a extração de uma quantidade significativa de proteínas, no entanto, o método de centrifugação resultou numa maior concentração de proteínas solubilizadas. A análise das imagens do gel 2D-PAGE revelou um maior número de spots no método de lise, quando comparado com os outros. Levando-se em consideração a qualidade dos resultados e as vantagens práticas do método de lise, este é recomendado como a melhor opção para extração de proteínas totais de Xcv para estudos de proteômica.

Arginine utilization in P. aeruginosa as the source of carbon, nitrogen, and energy is controlled by a complicated regulatory mechanism. While ArgR in the presence of exogenous arginine is required for auto-induction of the aotJQMOP-argR operon for arginine uptake and regulation, this operon is subjected to carbon catabolite repression via an unknown mechanism. This study demonstrated that succinate exerted a stronger repression effect than glucose or pyruvate on arginine induction of an aotJ::lacZ fusion in wild type PAO1. Expression of the aotJ::lacZ fusion was analyzed against three different backgrounds, cbrAB, crc, and vfr, that have been suggested to play a role in carbon catabolite repression. These mutations exerted a negative effect on the arginine-responsive induction to different extents, with the order of cbrAB > vfr > crc. A series of aotJ::lacZ fusions with deletions in the aotJ regulatory region were constructed and the effect of exogenous arginine examined in the argR mutant and its parent strain. The results indicated that a 250-bp sequence upstream of the ArgR operator is required for the optimal induction of the operon by exogenous arginine, and revealed the presence of a cryptic promoter (P0) in this region. Electromobility shift assays with crude cell-free extracts of PAO1 revealed that a DNA-binding protein other than ArgR binds to the aforementioned 250-bp region. Through reverse genetics, two regulatory proteins MvaT and MvaU were identified and specifically interacted with the aotJ-argR regulatory region. The MvaT/MvaU are involved in the regulation of the P0 promoter. The importance of MvaT and MvaU for bacterial growth was supported by the notion that no true mvaT mvaU double knockout mutant can be constructed. This is the first case to characterize the growth phenotypes of quasi-mvaT mvaU double mutants complemented with fusions for arginine-inducible expression of mvaT or mvaU. Further analysis of the physiological significance of MvaT and MvaU revealed their involvement in swarming response and pyocyanin synthesis. The defect in pyocyanin synthesis was correlated to the diminished level of PQS, an important chemical signal compound in the quorum sensing network of P. aeruginosa.

The use of autonomous aerial vehicles (UAVs) to explore unknown environments is a growing field of research; of particular interest is locating a target that emits a signal within an unknown environment. Several physical processes produce scalar signals that attenuate with distance from their source, such as chemical, biological, electromagnetic, thermal, and radar signals. The natural decay of the signal with increasing distance enables a gradient ascent method to be used to navigate toward the target. The UAVs navigate around obstacles whose positions are initially unknown; a hybrid controller comprised of overlapping control modes enables robust obstacle avoidance in the presence of exogenous inputs by precluding topological obstructions. Limitations of a distributed gradient augmentation approach to obstacle avoidance are discussed, and an alternative algorithm is presented which retains the robustness of the hybrid control while leveraging local obstacle position information to improve non-collision reliability. A heterogeneous swarm of multirotors demonstrates the target locating problem, sharing information over a multicast wireless private network in a fully distributed manner to form an estimate of the signal's gradient, informing the direction of travel toward the target. The UAVs navigate around obstacles, showcasing both algorithms developed for obstacle avoidance. Each UAV performs its own target seeking and obstacle avoidance calculations in a distributed architecture, receiving position data from an OptiTrack motion capture system, illustrating the applicability of the control law to real world challenges (e.g., unsynchronized clocks among different UAVs, limited computational power, and communication latency). Experimental and theoretical results are compared. / Master of Science / In this project, a new method for locating a target using a swarm of unmanned drones in an unknown environment is developed and demonstrated. The drones measure a signal such as a beacon that is being emitted by the target of interest, sharing their measurement information with the other drones in the swarm. The magnitude of the signal increases as the drones move toward the target, allowing the drones to estimate the direction to the target by comparing their measurements with the measurements collected by other drones. While seeking the target in this manner, the drones detect obstacles that they need to avoid. An issue that arises in obstacle avoidance is that drones can get stuck in front of an obstacle if they are unable to decide which direction to travel; in this work, the decision process is managed by combining two control modes that correspond to the two direction options available, using a robust switching algorithm to select which mode to use for each obstacle. This work extends the approach used in literature to include multiple obstacles and allow obstacles to be detected dynamically, enabling the drones to navigate through an unknown environment as they locate the target. The algorithms are demonstrated on unmanned drones in the VT SpaceDrones test facility, illustrating the capabilities and effectiveness of the methods presented in a series of scenarios.

Many species of bats primarily use echolocation, a type of active sensing wherein bats emit ultrasonic pulses and listen to echoes, for guidance and navigation. Swarms of such bats are a unique type of multi-agent systems that feature bats's echolocation and flight behaviors. In the work of this dissertation, we used bat swarming as an inspiration for multi-agent systems to study various topics which include predation success, active sensing, and collision avoidance. To investigate the predation success, we modeled a group of bats hunting a number of collectively behaving prey. The modeling results demonstrated the benefit of localized grouping of prey in avoiding predation by bats. In the topics regarding active sensing and collision avoidance, we studied individual behavior in swarms as bats could potentially benefit from information sharing while suffering from frequency jamming, i.e., bats having difficulty in distinguishing between self and peers's information. We conducted field experiments in a cave and found that individual bat increased biosonar output as swarm size increased. The experimental finding indicated that individual bat acquired more sensory information in larger swarms even though there could be frequency jamming risk. In a simulation wherein we modeled bats flying through a tunnel, we showed the increasing collision risk in larger swarms for bats either sharing information or flying independently. Thus, we hypothesized that individual bat increased pulse emissions for more sensory information for collision avoidance while possibly taking advantage of information sharing and coping with frequency jamming during swarming. / Ph. D.

Master of Science

A gama-proteobactéria Pseudomonas aeruginosa é um patógeno oportunista humano frequentemente associado a pacientes com queimadura grave e aos portadores de fibrose cística. O estabelecimento de infecção depende de uma série de fatores que contribuem para a virulência deste patógeno, dentre eles a produção de sideróforos e outros sistemas de captação de ferro. Pioverdina é o principal sideróforo sintetizado por bactérias do gênero Pseudomonas e linhagens deficientes na sua produção são incapazes de estabelecer infecção em modelos animais. A regulação da biossíntese deste sideróforo envolve a agregação entre as células, indicando a dependência de contato para completa indução da sua produção. O contato com uma superfície altera o comportamento das células e diversos fenótipos são dependentes deste sinal mecânico. PrlC é uma oligopeptidase A putativamente envolvida na degradação de peptídeo-sinais e PA14_00800, uma pequena proteína com domínio de função desconhecida, codificada por um gene imediatamente à jusante de prlC. Existem poucos trabalhos na literatura sobre PrlC e seus homólogos e nenhuma informação sobre PA14_00800. Este trabalho teve como objetivo elucidar o envolvimento de PrlC e PA14_00800 na regulação da produção de pioverdina por células em contato com uma superfície. Para estabelecer uma correlação na expressão destes genes, um estudo da organização gênica foi realizado por RT-PCR, confirmando que eles fazem parte do mesmo operon e, portanto, que a expressão destes genes é regulada pelos mesmos fatores. Ensaios classicamente modulados pelo segundo mensageiro c-di-GMP, como formação de biofilme e motilidade, não apresentaram variações nas linhagens mutantes ΔprlC, ΔPA14_00800 ou Δoperon, indicando que a deleção destes genes não altera significativamente os níveis de c-di-GMP nas células. A motilidade do tipo swarming é, no entanto, severamente afetada na linhagem ΔPA14_00800 quando o meio de cultura não contém cloreto de cálcio e glicose, indicando um defeito na sinalização celular ou requerimento energértico desta linhagem nestas condições. PA14_00800 regula a fluorescência de P. aeruginosa em meio sólido e semissólido, mas não em meio líquido. Esta fluorescência depende tanto de pioverdina quanto de PQS, umamolécula de comunicação celular fluorescente, e a possibilidade de outros fatores estarem envolvidos neste fenótipo ainda está sob investigação. Análise do transcritoma por RNASeq com a linhagem ΔPA14_00800 comparada à linhagem parental foi realizada a partir de colônias destas linhagens crescidas em M9 modificado. Genes envolvidos no sistema de secreção do tipo III e do tipo VI e na biossíntese de PQS apareceram dentre os genes diferencialmente expressos, bem como genes para o catabolismo de glicose. Este trabalho foi o primeiro a investigar o papel de PA14_00800 na fisiologia de P. aeruginosa, e os conhecimentos adquiridos aqui podem ser transpostos, com cautela, para compreensão da função dos homólogos de PA14_00800 em outras bactérias. / The gamma-proteobacterium Pseudomonas aeruginosa is a human opportunistic pathogen frequently associated with patients with severe burns and those with cystic fibrosis. The establishment of infection depends on several factors that contribute to the virulence of this pathogen, among them siderophore production and other iron uptake systems. Pyoverdine is the main siderophore synthesized by the bacteria of the genus Pseudômonas and pyoverdinedeficient strains are unable to establish infection in animal models. The regulation of biosynthesis of this siderophore involves cell aggregation, indicating contact dependency for complete induction of pyoverdine production. Surface contact alters cell behavior and several phenotypes are dependent on this mechanical cue. PrlC is an oligopeptidase A putatively involved in peptide-signals degradation and PA14_00800, a small protein with a domain of unknown function, encoded by a gene immediately downstream of prlC. There are few papers in the literature on PrlC and its homologues and no information on PA14_00800. This work aimed to elucidate the role of PrlC and PA14_00800 in surface-dependent regulation of pyoverdine production. To establish a correlation in the expression of these genes, a study of the gene organization was performed by RT-PCR, confirming that they are part of an operon and therefore the expression of these genes is regulated by the same factors. Traits classically modulated by the second messenger c-di-GMP, such as biofilm formation and motility, did not show variations in the ΔprlC, ΔPA14_00800 or Δoperon, indicating that the deletion of these genes does not significantly alter the levels of c-di-GMP within the cells. Swarming motility is, however, severely affected in the strain ΔPA14_00800 when the culture medium does not contain calcium chloride and glucose, indicating a cell signaling defect or energetic requirement under these conditions. PA14_00800 regulates surface-dependent fluorescence of P. aeruginosa, in solid and semi-solid medium. This fluorescence depends on both pyoverdine and PQS, a fluorescent cell-to-cell communication molecule, and the investigation of other putative factors involved in this phenotype is still under study. Transcriptomic analysis by RNASeq with the strain ΔPA14_00800 compared to PA14 was performed from colonies ofthese strains grown in modified M9 1% agar. Genes involved in the type III and type VI secretion systems, in PQS biosynthesis and glucose catabolism were differentially expressed. This work was the first to investigate the role of PA14_00800 in the physiology of P. aeruginosa, and the knowledge obtained here can be cautiously transposed to understanding the role of PA14_00800 homologues in other bactéria.

Coptotermes (Isoptera: Rhinotermitidae) é um gênero de grande importância econômica que, no sudeste do Brasil, é responsável pela maioria dos estragos em materiais celulósicos. Nenhum estudo taxonômico havia sido feito anteriormente, para as espécies das Américas e, até o momento, apenas cinco espécies eram conhecidas na região. Este gênero, com distribuição pantropical, apresenta cerca de 80 espécies descritas no mundo e, por ser um grupo grande e bastante diversificado, existe uma carência de trabalhos de revisão taxonômica e a identificação das espécies é, freqüentemente, uma tarefa difícil. No presente trabalho, foi feito o estudo taxonômico do gênero Coptotermes, nas Américas. Além das cinco espécies conhecidas, C. havilandi, C. formosanus, C. testaceus, C. crassus e C. niger, reconheço agora 13 novos táxons, que apresento aqui como espécies novas. Juntamente com as descrições, acrescentei dados de morfometria, desenhos esquemáticos, imagens de microscopia eletrônica de varredura, mapas com a distribuição geográfica e chaves de identificação de todas as espécies, com exceção de C. niger, pois não pude examinar os tipos, nem identificar qualquer amostra, com certeza, como sendo desta espécie. Achei preferível manter tal nome e a descrição traduzida de SNYDER (1922), mas não posso afirmar que se trata de uma boa espécie por falta de dados. Apesar da grande quantidade de material estudado (730 amostras), grandes áreas geográficas, em especial a região norte e nordeste do Brasil e outros países da América do Sul, ainda carecem de material representativo. Com a realização de coletas mais extensivas, acredito que este número possa duplicar. Foi dada ênfase no estudo de Coptotermes havilandi, principal praga de madeiras do sudeste brasileiro. Para esta espécie, foi feito o estudo da biologia das colônias iniciais, observando-se o comportamento pós-revoada, escolha do substrato de nidificação, taxa de sobrevivência das colônias, tempo de pré-postura, período de incubação dos ovos, tempo de duração e taxa de mortalidade entre os instares dos operários, muda e porcentagem da casta de soldados, número e viabilidade de indivíduos por colônia e rejeição das câmaras de criação, pelos reprodutores. Os resultados do estudo da biologia evidenciam a grande plasticidade de C. havilandi, no estabelecimento de novas colônias, em diversos tipos de substratos, até mesmo nos considerados pouco propícios e, também, sem a necessidade de contato com o solo. Também foi feito o estudo da fenologia das revoadas desta espécie, na cidade de São Paulo, destacando a sazonalidade e horário das revoadas, assim como razão sexual dos alados. Sua capacidade de fazer revoadas esporádicas, fora do período de pico (entre agosto e outubro), durante quase todo o ano, além de sua ampla distribuição horária, evidenciam a alta plasticidade de C. havilandi na dispersão dos indivíduos e a grande capacidade reprodutiva da espécie, com a produção de alados durante quase o ano inteiro. Por último, foi feita a descrição do ninho desta espécie, que mostrou um padrão semelhante a outras descrições feitas previamente, para esta e outras espécies do gênero. / Coptotermes (Isoptera: Rhinotermitidae) is a genus economically important, responsible for most of the damage to wood in southeastern Brazil. No taxonomic study on American species is available, and so far only five species have been described in the Americas. Coptotermes has a pantropical distribution, with approximately 80 species described worldwide. Taxonomic reviews for this genus are scarse and the identification of species of this diversified group is often difficult. This work is a taxonomic study of the genus Coptotermes in the Americas. In addition to the five described species, C. havilandi, C. formosanus, C. testaceus, C. crassus and C. niger, I describe thirteen new taxa that are presented as new species. Together with the descriptions of species I include morphometric data, schematic drawings, scanning electron microscopy pictures, maps of the distribution of each species and an identification key for all species except C. niger, for which I could not examine the types neither identify samples with certainty. Therefore, I chose rather to retain the name and description given by SNYDER (1922), although I cannot show that it is actually a good species. Despite the high number of samples analyzed (730) representative data from big geographical areas, especially north and northeastern Brazil and the other countries of South America are still lacking. More extensive collects in these areas potentially can double the number of the known Coptotermes species in the Americas. I focused on the study of C. havilandi, which is the main pest of wood in southeastern Brazil. The biology of incipient colonies has been studied, recording post-swarming behavior, nest choice, survival rate of colonies, duration of pre-oviposition, incubation time for eggs, each instar’s duration, death rate between worker instars, moulting and proportion of soldiers, number and viability of individuals per colony, and rejection from reproductive chambers by the reproductives. The study of the biology shows the high plasticity of C. havilandi to founding colonies in different types of substrates, including some considered as poorly suitable and some lacking contact with the soil. The study of the phenology of swarms in São Paulo city reveals the seasonality and timing of swarms, as well as the sexual ratio of alates. The capacity to produce sporadic dispersal flights (i.e. out of the peak period from August to October) almost year round and during a large part of the day demonstrate the high plasticity of C. havilandi in its dispersal habit and high reproductive capacity. Finally, I describe the nest of C. havilandi, showing a similar pattern to previous descriptions for this and other species of the genus.

The gram-negative marine bacterium Vibrio parahaemolyticus is a pathogen and a common worldwide cause of seafood-associated gastroenteritis. When grown on a surface, V. parahaemolyticus undergoes a dramatic differentiation to an elongated, highly flagellated swarmer cell from the short rod typical of swimming cells. Swarming motility is a complex form of adaptation to growth on a surface, and we developed a set of microarray experiments to examine the global gene expression changes that occur upon differentiation to the swarmer cell. We hypothesized that growth on a surface would elicit a specific response involving genes for motility and surface colonization and not the broad changes in physiology suggested by others to be co-regulated with swarming motility. By taking advantage of the two known signals required for swarmer cell induction (inhibiting polar flagellar rotation and limiting iron), the swarming response was artificially induced in liquid and used to define the set of genes associated with surface sensing by transcriptome analysis. This approach avoided the confounding physiological differences between growth in liquid and growth on a surface. Fifteen microarrays performed with different strains and growth conditions were used to define a concise set of about 70 genes that comprise the core set of surface-induced genes. This set includes genes encoding the surface motility system lateral flagella and virulence factors including a type three secretion system (T3SS1). I showed a biological consequence of the increased expression of T3SS1 genes, as surface-induced cells were more toxic in a tissue culture infection than either liquid-grown or surface-grown non-swarming mutants. I explored the role of calcium signaling in regulating the surface sensing network, as calcium seemed a pertinent signal to a marine organism and low calcium is a known inducing signal for T3SS in other organisms. Calcium was shown to enhance swarming motility and lateral flagellar gene expression. Microarrays were used to analyze the transcriptome response to growth with EGTA (a cation chelator commonly used to generate low calcium) or calcium. Surprisingly, both low and high calcium induced T3SS1 gene expression. The EGTA effect was determined to be the result of iron limitation, which was thus shown to be a new inducing signal for T3SS1. I overexpressed the master transcriptional regulator of the T3SS system, encoded by exsA, to define the entire set of T3SS1-associated genes. I found that ExsA was also a new regulator of the surface sensing regulon, which was repressed when exsA was overexpressed. Microarray analysis showed that calcium is a global regulator, controlling transcription of about 50 genes under the conditions tested. I characterized a new calcium-regulated transcription factor that we named CalR, and showed that CalR repressed swarming motility and T3SS1 gene expression. The transcription factor OpaR was previously known to repress swarming genes and control colony opacity. It is homologous to the output regulators of the quorum sensing pathway in other Vibrio species. I used microarray analysis and mutant strains to explore the functionality of the quorum sensing cascade in V. parahaemolyticus and define the OpaR regulon during growth on a surface. I showed that the quorum sensing regulator LuxO when active silences opaR as it does in other Vibrios, using a translational reporter fusion in opaR. I used microarray analysis to show that 323 genes are induced or repressed by OpaR. The surface-sensing regulon is repressed by OpaR. Many genes encoding proteins involved in virulence, signal transduction, and modulation of the signaling molecule cyclic dimeric GMP are regulated by OpaR. The quorum sensing controlled network of gene expression in V. parahaemolyticus is quite distinct from other Vibrios, with respect to both the specific nature as well as the direction of regulation of genes controlled by OpaR.

Le mouillage dʼun gel présente un intérêt fondamental pour la physique, lʼindustrie mais aussi en biologie: lors, par exemple, de la migration en masse de bactéries Bacilus Subtilis sur des milieux de culture gélosés où celle-ci synthétise un puissant tensioactif appelée surfactine. Un dispositif de reconstruction optique a été mis au point afin de suivre l'évolution de la surface libre d'une goutte posée à la surface d'un gel d'agar. Une goutte contenant de la surfactine s'étale spontanément. Lorsqu'elle entame sa rétraction, un front de surfactant apparaît tout autour de ses bords et se propage selon une dynamique de croissance radiale en loi de puissance du temps. Nous obtenons des exposants d'étalement remarqueblement faibles. Des scénarios expliquant cette dynamique lente sont proposés. Cette dynamique présente une dépendance vis à vis de la concentration du gel en polymères mais aussi vis à vis de la physico-chimie du milieu employé, montrant ainsi le caractère non-universel de cet exposant pour des gels aux propriétés mécaniques identiques. Nous discutons des similitudes entre nos observations et le swarming de B.Subtilis, pour lequel la dynamique du front et la croissance dendritique semblent fortement corrélées. Etonnamment, nous observons une situation de mouillage partiel dans le cas d'une goutte d'eau déposée à la surface d'un gel qui est pourtant constitué jusqu'à 99,5% du même liquide. Nous mesurons une hystérésis de mouillage importante partiellement lié au caractère déformable.du substrat Les modèles existants échouent à décrire nos mesures, nous proposons un modèle tenant compte de la tension de surface du gel qui prédit mieux nos observations.

Pseudomonas syringae pv. syringae B728a, an aggressive bacterial pathogen of bean, utilizes large surface populations and extracellular signaling to initiate a fundamental change from an epiphytic to a pathogenic lifestyle. Extracytoplasmic function (ECF) sigma (σ) factors serve as important regulatory factors in responding to various environmental signals. Bioinformatic analysis of the B728a genome has revealed 10 ECF sigma factors, five of which have high levels of sequence similarity to the FecI-type of ECF sigma factors and play a known role in the regulation of various iron transport systems. Because iron is essential for the induction of major virulence factors in B728a, I hypothesized that these FecI-type sigma factors may play a critical role in the bacterium’s transition between lifestyles. Deletion mutants of two FecI-type sigma factors, Psyr_1040 and Psyr_1107, in B728a have been created using homologous recombination based on the phage λ Red recombinase method. This study shows that the B728a FecI-type sigma factors, Psyr_1040 and Psyr_1107 are affected by conditions of iron stress, and influence the expression of putative outer membrane receptors and transmembrane sensors associated with these genes. Moreover, Psyr_1107 contributes to the expression of a cluster of predicted pili assembly genes downstream of it. Mutations in Psyr_1040 and Psyr_1107 affect the population levels of B728a in bean plants, since in planta growth of deletion mutants of B728a lacking Psyr_1040 and Psyr_1107 appears to be slower than wild-type B728a. In this thesis, the possible roles of Psyr_1040 and Psyr_1107 in the adaptation of B728a to a pathogenic lifestyle are addressed using a combination of phenotypic characterization and quantitative real-time PCR (qRT-PCR) analyses.