Análise proteômica, crescimento e composição celular da microalga Chlorella vulgaris sob autotrofia, mixotrofia e heterotrofia

Abstract

Some species of microalgae can change your metabolism as an answer to modifications in the environmental conditions. Chorella vulgaris (C. vulgaris) is an example of microalgae capable to growth in three different cultivation modes: autotrophic (CO2 and light), heterotrophic (glucose, without light) and mixotrophic (CO2, light and glucose). Although there are some studies about these different modes of growth in microalgae cultures, knowledge of cell behavior at molecular level at these conditions is still limited. In this context, the aim of this study was to identify the changes in the C. vulgaris proteomes as well as changes in growth profiles and cellular composition under autotrophic, heterotrophic and mixotrophic cultivation modes, in order to understand the molecular mechanisms used by microalgae to adapt to changes in growth conditions. The three different growth conditions significantly affect cell composition and proteome of C. vulgaris. The mixotrophic condition provided greater and faster cell growth, and there was not observed a period of adjustment after changes in growing conditions. The composition of lipids, carbohydrates, proteins, chlorophyll, starch and nitrogen from C. vulgaris differed significantly depending on the growth conditions studied. 204 proteins have been identified during the three growth regimes and transitions between them, and, while 19 proteins were identified only on mixotrophy, 8 were identified only in heterotrophic and 6 were identified only in autotrophy, indicating more complexity involved in growth condition during mixotrophic growth. It was found that various proteins involved in photosynthesis, CO2 fixation, tricarboxylic acid cycle, glycolysis, pentose phosphate pathway, among others metabolisms were otherwise regulated depending on the power source available for the cells. The presence of glucose, the light energy and CO2 induced or repressed expression of a large variety of cellular proteins, confirming the metabolic heterogeneity of growth conditions investigated. The major contribution of this thesis was the characterization of a third growth regime, the mixotrophy, which still remains little understood, and that is a growth regime to be explored due to the potential for CO2 utilization. This growth regime allows simultaneous use of light and an organic nutrient, increasing the productivity of biomass while also maintaining a high level of interesting photosynthesis compounds.