AlgaeNRG: Lipid accumulation in three freshwater microalgae under different levels of nitrogen limitation

The continuous increase in oil prices, in the demand of energy and global warming concerns gave a strong impetus to the development of renewable alternatives to fossil fuels. The interest in microalgae fuels is due to the high lipid content of some species and to the fact that lipid synthesis can be modulated by varying growth conditions. In particular nitrogen deficiency has been regarded as one of the most efficient approach to increase lipid (and oil) content in algae. Three freshwater microalgal strains (Neochloris oleoabundans UTEX# 1185, Chlorella vulgaris CCAP 211/11b and Scenedesmus obliquus SAG 276-3) were screened at laboratory scale to evaluate their biomass productivity and lipid content. In order to increase lipid content, the microalgae were cultivated under nitrogen limitation or starvation in 0.6 l bubbled tubes. As expected, the decrease in biomass productivity was high under nitrogen starvation (reduction of 54% for S.obliquus, 59% for N.oleoabundans and 64% for C.vulgaris), and less pronounced (between 11 and 25%) under nitrogen limitation. N.oleoabundans attained 27.8% lipid content, of which 40% were tryacylglicerides (TAGs) under nitrogen starvation and 35.7% of lipids, of which 25% were TAGs, under nitrogen limitation. C.vulgaris reached lower lipid and TAG contents. S. obliquus did not accumulate lipid under such conditions. The experiments showed that N.oleoabundans is a suitable strain for biofuel production due to its capacity to increase lipid content, especially the TAG fraction, under nutrient deprivation. Considerations are presented on the adoption of nitrogen limitation to obtain a significant increase in TAGs in freshwater microalgae without compromising biomass productivity.