Data of Dissertation

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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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