Data of Dissertation
Author: Roberta Fernandes Pinto
Title: Phosphate influence on growth, morphology and lipid accumulation in a chlorophyceae microalgae, Ankistrodesmus
Year: 2017. Full text (in Portuguese)
Abstract:
Microalgae have been used in different biotechnological applications, such as lipid production for biofuels, and production of carotenoid, vitamins and pigments. These applications favor studies on metabolism and structure of some of these microrganisms. Currently, it is known that diminishing nutrients in the medium, such as phosphate, promotes the accumulation of neutral lipids, such as triacylglycerols, inside lipid bodies in lineages of Chlorophycea microalgae. Therefore, the objective of this study was to select, characterize and evaluate a lineage of Chlorophyceae cultivated in medium with different phosphate concentrations, aiming for the accumulation of lipids that are of interest in biofuels production. The Ankistrodesmus, Monoraphidium, and Scenedesmus strains were previously selected. The three strains were observed by scanning electron microscopy and showed thin structures not yet described at the end of the cells of Ankistrodesmus and Scenedesmus, as well as wall structures of Monoraphidium and Ankistrodesmus. Based on the accumulation of lipid bodies and intracellular phosphate in the form of polyphosphate granules, Ankistrodesmus was selected as working strain, which was identified by molecular analysis of the sequence from the large subunit (LSU) from ribosomal DNA (rDNA) as Ankistrodesmus stipitatus. The selected microalgae were evaluated for growth, average volume, chlorophyll, photosynthetic rate, phosphate uptake from the medium, changes in polyphosphate granules, relationship between them and lipid accumulation under different concentrations of phosphate in the medium, and most common fatty acids. It was established that the absence of phosphate in the medium promoted a small diminishing in growth, variations in the average biovolume, but even without affecting the concentration of chlorophyll per cell, it diminished its photosynthetic activity. After addition of phosphate in the medium, the cells showed growth recovery, reduction in the average biovolume, elevation of photosynthetic activity and diminishing of lipids. It was observed that consumption of polyphosphate granules in Ankistrodesmus alters their morphology, allowing them to acquire a half-moon shape or present a central region less electron dense than the other part of the granule. Also, an accumulation of lipidic material was observed next to the polyphosphate granules, suggesting a direct relationship between these and the lipid bodies. Absence of phosphate in the medium promoted an increase in the accumulation of neutral lipids and favored the accumulation of saturated and monounsaturated fatty acids, with the five main fatty acids found corresponding to 80% of the total, being these C18: 3, C18: 1, C16: 0, C18: 2, and C16: 5. It is concluded that intracellularly accumulated phosphate is capable of supporting the growth of Ankistrodesmus microalgae, with a direct relationship between formation of lipid bodies and polyphosphate granules, and that the absence of phosphate in the culture medium favors the accumulation of fatty acids of lipids of interest for the production of biofuels. In summary, with this work we identified that Ankistrodesmus stipitatusis apropriated for utilization in the development of biofuels and can be a model to understand better the function of polyphosphate granules in microalgae.
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