Uso de interações moleculares, imunocitoquímica e genômica para caracterização de revestimentos de células de microalgas

Abstract

Microalgae are a very diverse group of photoautotrophic organisms with important ecological roles and are currently considered a source of compounds with high added value and raw material for biofuels production. Such compounds are found, most of time, inside the cell with the cell covering acting as a first barrier to access them. The rupture of algal cells is not always a simple and low-cost process due the varied repertoire of coating structures found in these organisms. Rigid coverings structures are poorly known or knowledge is restricted to a few species, being very unrepresentative considering the large diversity of microalgae. Cell surfaces also have a composition of biomolecules that are very variable among microalgae and are even less known. It is known that among these biomolecules carbohydrates and lectins are the most important, whose interaction between them mediate important physiological processes. Thus, both the rigid coverings structures and the cell surfaces hold important information about the ecology, morphology and physiology of cells. In this work, the main goals were to evaluate the current knowledge regarding the microalgae covering structures, to elucidate the cell wall and glycidic receptors compositions of the cell surfaces of six and five microalgae species respectively. For this, four chapters were prepared, corresponding to four manuscripts, which, taken as a whole, were based on a thorough review of the literature on the subject, application of cyto and immunocytochemistry techniques, use of glycodendrons as probes, use of confocal microscopy and also, for a species (Coelastrum microporum), sequencing and genomic analysis. The cell wall of the tested species showed a composition of cellulose, pectins and hemicelluloses that appears to be species-specific. This composition also varied according to the age of the cells, suggesting that the composition of the cell wall is associated with the physiological moment. Coelastrum microporum was the species that most resembled the plant wall in terms of composition and dynamics of pectin esterification. On cell 12 surfaces, glycidic receptors (lectins) for the D-mannose, L-fucose and Nacetylgalactosamine carbohydrates were detected. The composition of the receptors also varied between species and according to the age of the cells. The analysis of the C. microporum genome shows the presence of one lectin and many others encoding proteins (137) with a high chance of being lectins. More refined studies, including proteomics, are needed to characterize and confirm the identity and function of these carbohydrate receptor proteins.