Cultivo do dinoflagelado Symbiodinium glynnii em diferentes meios de cultura

Abstract

Microalgae are extremely important for the functioning of aquatic ecosystems, being mainly unicellular organisms and producers of photosynthetic pigments. As a cosmopolitan group, it is present in several ecosystems, where it helps in diverse ecosystem processes, from the maintenance of the base of the trophic web to the cycling of nutrients. They have applications in aquaculture covering from the nutrition of young organisms of species of commercial interest to the bioremediation of effluents produced. Its cultivation produces important biomolecules for nutritional, pharmacological, and biochemical use, as well as lipids for the production of biodiesel. Among the groups of microalgae, the dinoflagellates stand out for their expressive production of biomolecules of interest. However, they present cultivation difficulties related to the lack of detailed information about their growth and nutritional characteristics. Thus, the lack of information on the main cultivation variables (i.e., light, nutrient concentration, shear stress, etc.), complicates the biomass production of this promising microalgae group. The present dissertation aims to evaluate the growth performance and the biochemical composition, with emphasis on protein content, of the dinoflagellate Symbiodinium glynnii grown at different nitrogen-to-phosphorus ratios. Four treatments were used: Zero Nitrogen (0:1), Medium Nitrogen (7:1), Normal Nitrogen (14:1) - as control - and Double Nitrogen (28:1), obtained by modifying the NaNO3 solution of the f/2 medium. Three successive subcultures were performed in triplicate. Cultures were conducted in 250mL Erlenmeyer flasks, to which seawater (30 PSU) and B-complex vitamins were added. S. glynnii cells were inoculated at an initial concentration of 5 x 104 cells mL-1. These were maintained at 22 ± 1 °C, under constant aeration, the irradiance of 150 μmol photons m-2 s-1, and integral photoperiod. Growth was monitored using a Neubauer haematocytometer (72h), and the parameters DCM, K, μ, and TD were calculated. A photocolorimeter was used to analyse weekly N and P concentrations. The third sub cultivation was performed to obtain the production and yield of dry biomass, being submitted at the end to centrifugation, freeze-drying, and weighing. Dried biomass was subjected to determination of total protein (micro- Kjeldahl) and crude lipid content (AOCS Am 5-04). ZN did not show cellular increment in the second sub cultivation. S. glynnii show higher DCM when cultivated in MN (87.17 ± 8.46 x 104 cells mL-1), which was significantly different from treatments DN and NN. Higher K was verified in DN treatment (0.19 ± 0.02 div. day-1). For μ there were no significant differences between treatments (p > 0.05). Lower TD in DN treatment (5.26 ± 0.38 days). The highest dry biomass yield found in DN was 753.33 ± 14.14 mg L-1, as well as daily productivity (31.39 ± 0.59 mg L-1 day-1). Growth curves showed consistent growth, as well as the N:P uptake, showed the expected decay in MN, NN, and DN. The best growth variables were obtained when higher concentrations of N in the N:P ratio (DN - 28:1) were used, combined with higher yields of biomass and total protein content (31.51 ± 0.15 %). N concentrations in the N:P ratios between 14:1 (NN) and 28:1 (DN) is recommended for the cultivation of Symbiodinium glynnii. Further studies are needed to understand the mechanisms that regulate the metabolism of these dinoflagellates.