Molecular hydrogen is a potential energy carrier for the future. Nitrogen-fixing cyanobacteria are a group of photosynthetic microorganisms with the inherent ability to produce molecular hydrogen via the enzyme complex nitrogenase. This hydrogen is not released, however, but is recaptured by the bacteria using an uptake hydrogenase. In this thesis, genes involved in cyanobacterial hydrogen metabolism were examined, and the possibility of employing genetically modified cyanobacteria for hydrogen production was investigated. Nostoc punctiforme PCC 73102 (ATCC 29133) is a nitrogen-fixing filamentous cyanobacterium containing an uptake hydrogenase encoded by hupSL. The transcription of hupSL was characterised, and putative regulatory elements in the region upstream of the transcription start site were identified. One of these, a binding motif for the global nitrogen regulator NtcA, was further investigated by mobility shift assays, and it was found that the motif is functional in binding NtcA. Also, a set of genes involved in maturation of hydrogenases was identified in N. punctiforme, the hypFCDEAB operon. These genes were found to be situated upstream of hupSL in the opposite direction, and they were preceded by a previously unknown open reading frame, that was found to be transcribed as part of the same operon. The potential for hydrogen production by filamentous cyanobacteria was investigated by studying mutant strains lacking an uptake hydrogenase. A mutant strain of N. punctiforme was constructed, where hupL was inactivated. It was found that cultures of this strain evolve hydrogen during nitrogen fixation. Gas exchange in the hupL- mutant and in wild type N. punctiforme was measured using a mass spectrometer, and conditions under which hydrogen production from the nitrogenase could be increased at the expense of nitrogen fixation were identified. Growth and hydrogen production in continuous cultures of a Hup- mutant of the related strain Nostoc PCC 7120 were also studied. This thesis advances the knowledge about cyanobacterial hydrogen metabolism and opens possibilities for further development of a process for hydrogen production using filamentous cyanobacteria.

L'incessant augment del nombre de seqüències genòmiques, juntament amb l'increment del nombre de tècniques experimentals de les que es disposa, permetrà obtenir el catàleg complet de les funcions cel.lulars de diferents organismes, incloent-hi la nostra espècie. Aquest catàleg definirà els fonaments sobre els que es podrà entendre millor com els organismes funcionen a nivell molecular. Al mateix temps es tindran més pistes sobre els canvis que estan associats amb les malalties. Per tant, la seqüència en brut, tal i com s'obté dels projectes de seqüenciació de genomes, no té cap valor sense les anàlisis i la subsegüent anotació de les característiques que defineixen aquestes funcions. Aquesta tesi presenta la nostra contribució en tres aspectes relacionats de l'anotació dels gens en genomes eucariotes. Primer, la comparació a nivell de seqüència entre els genomes humà i de ratolí es va dur a terme mitjançant un protocol semi-automàtic. El programa de predicció de gens SGP2 es va desenvolupar a partir d'elements d'aquest protocol. El concepte al darrera de l'SGP2 és que les regions de similaritat obtingudes amb el programa TBLASTX, es fan servir per augmentar la puntuació dels exons predits pel programa geneid, amb el que s obtenen conjunts d'anotacions més acurats d'estructures gèniques. SGP2 té una especificitat que és prou gran com per que es puguin validar experimentalment via RT-PCR. La validació de llocs d'splicing emprant la tècnica de la RT-PCR és un bon exemple de com la combinació d'aproximacions computacionals i experimentals produeix millors resultats que per separat. S'ha dut a terme l'anàlisi descriptiva a nivell de seqüència dels llocs d'splicing obtinguts sobre un conjunt fiable de gens ortòlegs per humà, ratolí, rata i pollastre. S'han explorat les diferències a nivell de nucleòtid entre llocs U2 i U12, pel conjunt d'introns ortòlegs que se'n deriva d'aquests gens. S'ha trobat que els senyals d'splicing ortòlegs entre humà i rossegadors, així com entre rossegadors, estan més conservats que els llocs no relacionats. Aquesta conservació addicional pot ser explicada però a nivell de conservació basal dels introns. D'altra banda, s'ha detectat més conservació de l'esperada entre llocs d'splicing ortòlegs entre mamífers i pollastre. Els resultats obtinguts també indiquen que les classes intròniques U2 i U12 han evolucionat independentment des de l'ancestre comú dels mamífers i les aus. Tampoc s'ha trobat cap cas convincent d'interconversió entre aquestes dues classes en el conjunt d'introns ortòlegs generat, ni cap cas de substitució entre els subtipus AT-AC i GT-AG d'introns U12. Al contrari, el pas de GT-AG a GC-AG, i viceversa, en introns U2 no sembla ser inusual. Finalment, s'han implementat una sèrie d'eines de visualització per integrar anotacions obtingudes pels programes de predicció de gens i per les anàlisis comparatives sobre genomes. Una d'aquestes eines, el gff2ps, s'ha emprat en la cartografia dels genomes humà, de la mosca del vinagre i del mosquit de la malària, entre d'altres. El programa gff2aplot i els filtres associats, han facilitat la tasca d'integrar anotacions de seqüència amb els resultats d'eines per la cerca d'homologia, com ara el BLAST. S'ha adaptat també el concepte de pictograma a l'anàlisi comparativa de llocs d splicing ortòlegs, amb el desenvolupament del programa compi. / El aumento incesante del número de secuencias genómicas, junto con el incremento del número de técnicas experimentales de las que se dispone, permitirá la obtención del catálogo completo de las funciones celulares de los diferentes organismos, incluida nuestra especie. Este catálogo definirá las bases sobre las que se pueda entender mejor el funcionamiento de los organismos a nivel molecular. Al mismo tiempo, se obtendrán más pistas sobre los cambios asociados a enfermedades. Por tanto, la secuencia en bruto, tal y como se obtiene en los proyectos de secuenciación masiva, no tiene ningún valor sin los análisis y la posterior anotación de las características que definen estas funciones. Esta tesis presenta nuestra contribución a tres aspectos relacionados de la anotación de los genes en genomas eucariotas. Primero, la comparación a nivel de secuencia entre el genoma humano y el de ratón se llevó a cabo mediante un protocolo semi-automático. El programa de predicción de genes SGP2 se desarrolló a partir de elementos de dicho protocolo. El concepto sobre el que se fundamenta el SGP2 es que las regiones de similaridad obtenidas con el programa TBLASTX, se utilizan para aumentar la puntuación de los exones predichos por el programa geneid, con lo que se obtienen conjuntos más precisos de anotaciones de estructuras génicas. SGP2 tiene una especificidad suficiente como para validar esas anotaciones experimentalmente vía RT-PCR. La validación de los sitios de splicing mediante el uso de la técnica de la RT-PCR es un buen ejemplo de cómo la combinación de aproximaciones computacionales y experimentales produce mejores resultados que por separado. Se ha llevado a cabo el análisis descriptivo a nivel de secuencia de los sitios de splicing obtenidos sobre un conjunto fiable de genes ortólogos para humano, ratón, rata y pollo. Se han explorado las diferencias a nivel de nucleótido entre sitios U2 y U12 para el conjunto de intrones ortólogos derivado de esos genes. Se ha visto que las señales de splicing ortólogas entre humanos y roedores, así como entre roedores, están más conservadas que las no ortólogas. Esta conservación puede ser explicada en parte a nivel de conservación basal de los intrones. Por otro lado, se ha detectado mayor conservación de la esperada entre sitios de splicing ortólogos entre mamíferos y pollo. Los resultados obtenidos indican también que las clases intrónicas U2 y U12 han evolucionado independientemente desde el ancestro común de mamíferos y aves. Tampoco se ha hallado ningún caso convincente de interconversión entre estas dos clases en el conjunto de intrones ortólogos generado, ni ningún caso de substitución entre los subtipos AT-AC y GT-AG en intrones U12. Por el contrario, el paso de GT-AG a GC-AG, y viceversa, en intrones U2 no parece ser inusual. Finalmente, se han implementado una serie de herramientas de visualización para integrar anotaciones obtenidas por los programas de predicción de genes y por los análisis comparativos sobre genomas. Una de estas herramientas, gff2ps, se ha utilizado para cartografiar los genomas humano, de la mosca del vinagre y del mosquito de la malaria. El programa gff2aplot y los filtros asociados, han facilitado la tarea de integrar anotaciones a nivel de secuencia con los resultados obtenidos por herramientas de búsqueda de homología, como BLAST. Se ha adaptado también el concepto de pictograma al análisis comparativo de los sitios de splicing ortólogos, con el desarrollo del programa compi. / The constantly increasing amount of available genome sequences, along with an increasing number of experimental techniques, will help to produce the complete catalog of cellular functions for different organisms, including humans. Such a catalog will define the base from which we will better understand how organisms work at the molecular level. At the same time it will shed light on which changes are associated with disease. Therefore, the raw sequence from genome sequencing projects is worthless without the complete analysis and further annotation of the genomic features that define those functions. This dissertation presents our contribution to three related aspects of gene annotation on eukaryotic genomes. First, a comparison at sequence level of human and mouse genomes was performed by developing a semi-automatic analysis pipeline. The SGP2 gene-finding tool was developed from procedures used in this pipeline. The concept behind SGP2 is that similarity regions obtained by TBLASTX are used to increase the score of exons predicted by geneid, in order to produce a more accurate set of gene structures. SGP2 provides a specificity that is high enough for its predictions to be experimentally verified by RT-PCR. The RT-PCR validation of predicted splice junctions also serves as example of how combined computational and experimental approaches will yield the best results. Then, we performed a descriptive analysis at sequence level of the splice site signals from a reliable set of orthologous genes for human, mouse, rat and chicken. We have explored the differences at nucleotide sequence level between U2 and U12 for the set of orthologous introns derived from those genes. We found that orthologous splice signals between human and rodents and within rodents are more conserved than unrelated splice sites. However, additional conservation can be explained mostly by background intron conservation. Additional conservation over background is detectable in orthologous mammalian and chicken splice sites. Our results also indicate that the U2 and U12 intron classes have evolved independently since the split of mammals and birds. We found neither convincing case of interconversion between these two classes in our sets of orthologous introns, nor any single case of switching between AT-AC and GT-AG subtypes within U12 introns. In contrast, switching between GT-AG and GC-AG U2 subtypes does not appear to be unusual. Finally, we implemented visualization tools to integrate annotation features for gene- finding and comparative analyses. One of those tools, gff2ps, was used to draw the whole genome maps for human, fruitfly and mosquito. gff2aplot and the accompanying parsers facilitate the task of integrating sequence annotations with the output of homologybased tools, like BLAST.We have also adapted the concept of pictograms to the comparative analysis of orthologous splice sites, by developing compi.

No description available.

Para obter resultados rápidos e confiáveis que permitam o monitoramento da segurança microbiológica de alimentos, seja pela indústria ou pelos órgãos de fiscalização, diversos métodos alternativos têm sido desenvolvidos para a detecção e quantificação de Salmonella. Os propósitos do estudo foram avaliar a viabilidade de emprego do QIAamp® DNA Stool Mini Kit para extração e purificação de DNA de Salmonella; validar ensaios baseados em PCR-tempo real (PCR-RT) para quantificar o DNA de Salmonella empregando ttr ou tuf e desenvolver um ensaio para quantificar Salmonella baseado na transcriptase reversa-PCR-tempo real (RT-PCR-RT). Para avaliação do QIAamp® DNA Stool Mini Kit empregaram-se fezes coletadas diretamente do reto de animais infectados ou não, sendo estas últimas artificialmente contaminadas e submetidas à extração segundo protocolo do fabricante. As amostras de DNA isoladas foram quantificadas empregando um ensaio Salmonella-específico PCR-RT utilizando como alvo o lócus ttr. O mesmo ensaio foi utilizado para células de Salmonella provenientes de meio de cultura. O ensaio PCR-RT baseado no alvo tuf foi validado empregando-se primeiramente cepas de diferentes sorotipos de Salmonella e de outras Enterobacteriaceae. A seguir sua eficiência foi avaliada para alimentos-modelo (ave e suíno) artificialmente contaminadas com elevada (≈ 6 log UFC/mL) e baixa (≈ 2 log UFC/mL) população de Salmonella Typhimurium DT 104. A validação do método quantitativo de Salmonella por RT-PCR-RT foi realizada primeiramente com células em meio de cultura e posteriormente nos mesmos alimentos-modelo utilizados para PCR-RT. Em ambos os métodos, alíquotas dos alimentos-modelo foram mantidas a 20 ºC e a 8 ºC, sendo examinadas em diferentes tempos pós-inoculação. Como controle empregou-se a enumeração de microrganismos mesófilos totais e de Salmonella por técnicas convencionais. A taxa de recuperação de Salmonella em fezes suínas artificialmente inoculadas, após tratamento com QIAamp® DNA Stool Kit, variou entre 25% a 50%, dependendo da quantidade inicial de células. Empregando o DNA extraído e submetendo-o à PCR-RT para o ttr obteve-se limite de detecção de 2,8 log UFC eq/g de fezes; método que foi menos sensível que o convencional. A quantificação de Salmonella por PCR-RT empregando tuf apresentou limite de detecção menor que 1 log UFC eq. Os resultados obtidos com este método, empregando-se células em meio de cultura ou alimentos-modelo, foram, de maneira geral, ligeiramente inferiores aos do método convencional. A eficiência de amplificação para PCR-RT e tuf foi de 94%. O método RT-PCR-RT apresentou limite de detecção semelhante ao obtido com o ttr (2 log UFC eq) e sua eficiência de amplificação foi de 100%. Observou-se que tuf é expresso na fase logarítmica de multiplicação bacteriana, o que o torna um bom indicador da viabilidade de Salmonella. / In order to get fast and trustworthy results that allow monitoring the microbiological food safety either by industries or governmental agencies, diverse alternative methods have been developed for Salmonella detection and quantification. The purposes of this study were to evaluate the viability of the use of QIAamp® DNA Stool Mini Kit for Salmonella DNA extraction and purification; to validate assays based on real time-PCR (PCR-RT) to quantify Salmonella DNA by using ttr or tuf, and to develop an assay to quantify Salmonella based on reverse transcriptase- PCR-real time (RT-PCR-RT). For QIAamp® DNA Stool Mini Kit evaluation feces taken directly from the rectum of infected or health animals were used, with the former being artificially contaminated. Samples were submitted to DNA extraction, according to manufacturers protocol. The isolated DNA were quantified using a Salmonella-specific PCR-RT targeting the ttr locus. The same assay was used for Salmonella cells originated from culture medium. The PCR-RT assay with tuf as target was first validated employing different Salmonella serovars and other Enterobacteriaceae strains. After, its efficiency was evaluated on food-models (chicken and swine) spiked with high (≈ 6 log CFU/mL) and low (≈ 2 log CFU/mL) Salmonella Typhimurium DT 104 populations. The validation of the quantitative RT-PCR-RT method was first conducted with cells grown in culture medium, and then in the same food-model used for PCR-RT. For both methods aliquots of foodmodels were maintained at 20 ºC and 8 ºC being evaluated at different incubation times. Enumeration of total mesophilic microorganisms and Salmonella based on conventional methods were used as controls. The DNA recovery rate in swine feces artificially inoculated, after QIAamp® DNA Stool Mini Kit treatment, was between 25% to 50% depending the initial amount of cells. Using the extracted DNA and submitting it to PCR-RT for ttr a detection level of 2,8 CFU eq/g of feces was obtained. This method showed lower sensitivity than the conventional. Salmonella quantification by PCR-RT employing tuf showed a detection level lower than 1 log CFU eq. The results obtained with this method and cells suspended in culture medium or in food-model systems were, in general slightly lower that those obtained with the conventional method. The efficiency of amplification for PCR-RT tuf was 94%. Detection limit of RT-PCR-RT was similar to that of ttr (2 log CFU eq) and efficiency of amplification was 100%. tuf was expressed in logarithmic phase of bacteria growth curve showing that it is a good viability indicator for Salmonella.

When tomato Craigella is infected with Verticillium dahliae Dvd-E6 (Dvd-E6), a tolerant state is induced with substantial pathogen load, but few symptoms. Unexpectedly, these plants are more robust and taller with Dvd-E6 behaving as an endophyte. Some endophytes can protect plants from virulent pathogens. This research was undertaken to improve understanding of the cellular and molecular nature of Verticillium tolerance in tomato, especially whether infection by Dvd-E6 can protect Craigella from virulent V. dahliae, race 1 (Vd1). To permit mixed infection experiments a restriction fragment length polymorphism (RFLP)-based assay was developed and used for differentiating Dvd-E6 from Vd1, when present in mixed infections. The results suggested that protection involves molecular interplay between Dvd-E6 and Vd1 in susceptible Craigella (CS) tomatoes, resulting in restricted Vd1 colonization. Further studies showed a dramatic reduction of Vd1 spores and mycelia. To examine genetic changes that account for these biological changes, a customized DNA chip (TVR) was used to analyze defense gene mRNA levels. The defense gene response was categorized into four groups. Group 1 was characterized by strong induction of defense genes followed by suppression. However, Vd1-induced gene suppression was blocked by Dvd-E6 in mixed infections. These genes included some transcription factors and PR proteins such as class IV chitinases and beta glucanases which are known to target fungal spores and mycelia. Experiments also were repeated with a Craigella resistant (CR) isoline containing a fully active Ve locus (Ve1+ and Ve2+). The biological results showed that the presence of the Ve1+ allele resulted in restricted Vd1 colonization and, in a mixed infection with Dvd-E6, Vd1 was completely eliminated from the plant stem. Surprisingly, there was no significant increase in defense gene mRNAs. Rather, elevated basal levels of defense gene products appeared sufficient to combat pathogen attack. To investigate functional effects of the genetic changes observed, an inducible RNAi knockdown vector for a defense gene (TUS15G8) with unknown function (pMW4-TUS15G8) as well as the Ve2 resistance gene (pMW-Ve2) was prepared as a initial step for future transformation analyses. Taken together the results reveal intriguing but complex biological and molecular changes in mixed infections, which remain a basis for future experiments and potential agricultural benefits. / Canadian Commonwealth Scholarship and Fellowship Plan

Neurotrophins and their receptors are key molecules in the development of thenervous system. Neurotrophin-3 binds preferentially to its high-affinity receptorNTRK3, which exists in two major isoforms in humans, the full-length kinaseactiveform (150 kDa) and a truncated non-catalytic form (50 kDa). The twovariants show different 3'UTR regions, indicating that they might be differentiallyregulated at the post-transcriptional level. In this work we explore howmicroRNAs take part in the regulation of full-length and truncated NTRK3,demonstrating that the two isoforms are targeted by different sets of microRNAs.We analyze the physiological consequences of the overexpression of some of theregulating microRNAs in human neuroblastoma cells. Finally, we providepreliminary evidence for a possible involvement of miR-124 - a microRNA with noputative target site in either NTRK3 isoform - in the control of the alternativespicing of NTRK3 through the downregulation of the splicing repressor PTBP1. / Las neurotrofinas y sus receptores constituyen una familia de factores crucialespara el desarrollo del sistema nervioso. La neurotrofina 3 ejerce su funciónprincipalmente a través de una unión de gran afinidad al receptor NTRK3, del cualse conocen dos isoformas principales, una larga de 150KDa con actividad de tipotirosina kinasa y una truncada de 50KDa sin dicha actividad. Estas dos isoformasno comparten la misma región 3'UTR, lo que sugiere la existencia de unaregulación postranscripcional diferente. En el presente trabajo se ha exploradocomo los microRNAs intervienen en la regulación de NTRK3, demostrando que lasdos isoformas son reguladas por diferentes miRNAs. Se han analizado lasconsecuencias fisiológicas de la sobrexpresión de dichos microRNAs utilizandocélulas de neuroblastoma. Finalmente, se ha estudiado la posible implicación delmicroRNA miR-124 en el control del splicing alternativo de NTRK3 a través de laregulación de represor de splicing PTBP1.