Memoria para optar al Título Profesional de Ingeniera Agrónoma / Las microalgas son capaces de producir diferentes compuestos de importancia nutricional, siendo utilizadas en acuicultura, alimentación animal y nutrición humana. Esta capacidad depende, entre otros factores, de la concentración de nutrientes, lo que altera la composición bioquímica de las microalgas. Se evaluó el efecto de la concentración de la solución nutritiva de Hoagland y Arnon II modificada sobre la biomasa fresca, contenido de algunas biomoléculas de interés y sobre la capacidad antioxidante de microalgas Chlamydomonas, género que es utilizado como sistema modelo de investigación en biología celular pero que hasta el momento no ha sido estudiado desde el punto de vista nutricional ni desde sus potencialidades comerciales. Mediante la combinación de dos métodos de aislamiento: rayado en agar y dilución seriada, se logró aislar microalgas Chlamydomonas para su posterior cultivo en una cámara acondicionada para el crecimiento de las microalgas bajo condiciones controladas de temperatura, fotoperiodo y radiación. Durante la etapa de cultivo en matraces de 500 mL se aplicaron cinco tratamientos con distinta concentración de nutrientes (solución nutritiva de Hoagland y Arnon II modificada, al 25, 50, 100, 150 y 200%). Se realizaron muestreos durante 31 días (día por medio), obteniendo curvas de crecimiento poblacional típicas de microorganismos, esto permitió discutir el efecto de la solución nutritiva en cuatro días representativos (días 9, 17, 25 y 31) del crecimiento poblacional. Durante estos cuatro días no se detectaron diferencias que pudieran indicar alguna tendencia o efecto de la concentración de la solución nutritiva sobre la producción de biomasa, ni sobre el contenido de proteínas solubles, hidratos de carbonos, clorofila a, clorofila b y carotenoides, durante el periodo de cultivo. La capacidad antioxidante tampoco se vio afectada por las distintas concentraciones de la solución nutritiva. Sobre la base de los resultados anteriores, se podría sugerir que el mejor momento para cosechar microalgas con fines comerciales correspondería el día 25, el cuál se sitúa hacia el final de la fase de crecimiento exponencial. Durante dicho día el tratamiento con la menor concentración de la solución nutritiva no presentó diferencias en biomasa fresca producida, contenido de proteínas solubles y carotenoides, como tampoco en capacidad antioxidante, en comparación con los otros tratamientos. De acuerdo a los resultados se puede concluir que las cinco concentraciones de la solución nutritiva permiten un adecuado crecimiento en Chlamydomonas, satisfaciendo sus requerimientos nutricionales para producción de biomasa fresca y de biomoléculas de interés comercial. / In this study was evaluated the effect of Hoagland and Arnon II nutrient solution in the production of fresh biomass, biomolecules content and the antioxidant capacity of the microalgae Chlamydomonas, genus that is commonly used as a research model system in cellular biology, however until now this studies didn’t analyses the nutritional or economics point of view. The population growing curves was used to analyze the effect of the nutrient solution in four days (9, 17, 25 and 31). The result didn’t show effects of the nutrients solution application in the biomass production, soluble proteins, carbohydrates, chlorophyll a, chlorophyll b, carotenoids and the antioxidant capacity. With this result I suggest the 25 day as the best harvest day of the microalgae with commercial purpose. Finally, all treatment allowed an adequate growth of Chlamydomonas, fulfilled the nutritional requirements to fresh biomass and commercial biomolecules production.

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The eyespot of the biflagellate unicellular green alga Chlamydomonas reinhardtii is a complex organelle that facilitates directional responses of the cell to environmental light stimuli. The eyespot, which assembles de novo after every cell division and retains a distinctive association with the microtubule cytoskeleton, comprises an elliptical patch of rhodopsin photoreceptors in the plasma membrane and stacks of carotenoid-rich pigment granule arrays in the chloroplast and serves as a model for understanding how organelles are formed and placed asymmetrically in the cell. This study describes the roles of several factors in the assembly and positioning of the eyespot. Two loci, EYE2 and EYE3, define factors involved in the formation and organization of the eyespot pigment granule arrays. Whereas EYE3, a serine/threonine kinase of the ABC1 family, localizes to pigment granules, EYE2 localization corresponds to an area of the chloroplast envelope in the eyespot. These proteins play interdependent roles: EYE2 and the ChR1 photoreceptor co-position in the absence of pigment granules, and the pigment granules are required to maintain the shape and integrity of the EYE2/ChR1 patch. The miniature-eyespot locus MIN2 affects eyespot size and likely regulates the amount of material available for eyespot assembly. The MLT2 locus regulates eyespot size, number, and asymmetry. A novel locus, PEY1, modulates the position of the eyespot on the anterior-posterior axis by affecting microtubule rootlet length. A working model is developed wherein rootlet microtubule-directed photoreceptor localization establishes connections in the chloroplast envelope with EYE2, which directs the site for pigment granule array assembly, and MLT2 is proposed to negatively regulate the levels of eyespot proteins.

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Ongoing global change has made understanding the factors that affect adaptation and survival of populations in the context of changing environments a central problem in evolutionary biology. Special focus has been given to the probability of survival through genetic adaptation to lethal environments; a process termed evolutionary rescue. Many studies of this process, both theoretical and empirical, have been carried out over the last two decades. As a result, we now understand how a number of factors may affect the probability of population survival. However, two factors that are known to affect evolutionary responses, mode of reproduction and interspecific interaction, have received limited attention. The main aim of my work was to investigate whether and how mode of reproduction and negative interspecies interactions (competition) affect the probability of evolutionary rescue. To achieve this goal, I set up a series of selection experiments, by propagating populations of unicellular alga Chlamydomonas reinhardtii in various stressful conditions, and monitored their survival and fitness. To investigate the effect of sex in these experiments, I manipulated mode of reproduction, by constructing the experimental populations allowed to reproduce either only sexually or asexually or both. To investigate the effect of competition, I manipulated the presence of the competitor(s) in the experimental populations, by cultivating them either in presence or absence of the competitor. I first tested the effect of rate of environmental deterioration and mode of reproduction on extinction dynamics and evolutionary rescue of the experimental populations. I found positive correlation between the rate of extinctions and the rate of environmental deterioration. The experiment revealed an interaction between mode of reproduction and the rate of deterioration, manifested through significantly reduced extinction rate of sexual populations relative to asexual populations in environment deteriorating at intermediate rate. I then investigated the effect of sex and competition on the probability of evolutionary rescue, by propagating the experimental populations in environment deteriorating in a simple way (the change comprising a single abiotic factor) and complex way (the change of both abiotic and biotic factors). I found the negative effect of competition on the probability of evolutionary rescue, and beneficial effect of sex in both types of environmental deterioration, reflected in higher number of rescued populations relative to asexual group. I then tested whether phylogenetic relatedness between a competitor and the focal species and the extent of their ecological similarity affect the likelihood of evolutionary rescue, by subjecting the experimental populations to the presence of 10 different competitors, isolated from two different types of habitats, and each being positioned on a different branch of the phylogenetic tree of Chlamydomonas genus. The probability of evolutionary rescue was contingent on the identity of a competitor species, but the results showed no significant effects of phylogenetic relatedness and ecological similarity. Finally, I investigated which experimental factors could potentially select for the long-term maintenance of sex, by subjecting the experimental populations to different types of selective environments (directional and fluctuating change of abiotic factors, the presence of the competitor) and monitoring the frequency of sex over the course of time. No selective environment significantly increased the rate of sex in the experimental populations. In contrast, I found reduction in frequency of sex in the populations subjected to fluctuating environmental change. My results demonstrate that both mode of reproduction and competition affect the probability of evolutionary rescue, which is generally positively affected by sex and negatively affected by competition. However, these general effects may be altered by other factors, namely mode of environmental change and the identity of the competitor species.

Thesis (Ph. D.)--University of Texas at Austin, 2000. / Vita. Includes bibliographical references (leaves 110-137). Available also in a digital version from Dissertation Abstracts.

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Green algae have evolved several photo-protective responses to cope with high-light stress. The present study examines the metabolic changes during photoacclimation to high-light in Chlamydomonas reinhardtii using nuclear magnetic resonance and mass spectrometry. Using principal component analysis, a clear metabolic response to highlight intensity was observed on global metabolite pools in Chlamydomonas, with major changes in the levels of amino acids and related nitrogen metabolites. Amino acid biosynthesis was induced during short-term photoacclimation presumably to alleviate excess excitation pressure in the plastid. An increase in mitochondrial metabolism through downstream photorespiratory and glyoxylate metabolism, pathways thought to act in a photo-protective capacity, was also observed. Long-term light stress resulted in a significant increase in antioxidant metabolites, ascorbate and dehydroascorbate. These results suggest that metabolism plays a direct role in coping with the imbalance in the excess excitation pressure generated during high-light stress; however, this metabolomics survey has generated additional questions about the roles of nitrogen assimilation associated metabolites in photoacclimatory responses to high-light in Chlamydomonas.