Efeitos da depleção de nitrogênio sobre a biomassa e produção lipídica lipídica de três espécies de microalgas fitoplânticas

Abstract

The use of lipids from microalgae biomass has been described as a promising alternative to the petro-diesel industry and involves steps such as microalgae cultivation, biomass separation and lipid extraction. To facilitate the large-scale production, it is necessary to select the most productive species, reduce production costs and determine optimal growing conditions. Chlorella, Desmodesmus and Ankistrodemsus are genus with favorable characteristics for commercial production, being selected then, one species from each one in the present work. The aim of the study was to evaluate different growth conditions in Ankistrodemsus fusiformis, Chlorella vulgaris and Desmodesmus spinosus aiming to enhance the biomass production and total lipid content. The algae were identified and grown in the laboratory under controlled temperature conditions of 26 ºC (±1), aeration by bubbling at ambient pressure and light provided by fluorescent lamps at an intensity of 47,25 µmol photons m-2.s-1 (3500 lux), 12 hours photoperiod and pH 7, under two stressful concentrations of sodium nitrate (0.10 g/L and 0.05 g/L). The cultures lasted an average of 16 days, with growth curves constructed with optical spectrophotometry data collected every 48 hours, and the biomass was obtained at the end of the cultures by centrifugation and lyophilisation of each experimental unit. For extraction of total lipids, were used the mixture chloroform: methanol (1:2) according to Bligh & Dyer (1959) method. The stress treatments in D. spinosus resulted in increased lipid accumulation, an increase of up to 149.7%, although with a drastic decrease in growth and biomass. In C. vulgaris, the stress treatments were found to only slightly increase the dry weight and lipid content, with no significant difference between the treatments and the control. Similarly, A. fusiformis showed no significant responses to stress by reduction of sodium nitrate in the medium, with a slight decrease of lipid content and increased growth and biomass. With different answers for each studied species, we highlight the need for knowledge of both the physiology and autecology of the strain to be grown on a commercial scale aimed at the production of fatty acids for biodiesel purposes.