Growth and lipid profile of Tetrasel mis sp. KY114885 in a combined two-stage N-deficient cultivation

Microalgae are renewable resources for biodiesel production due to high lipid accumulation. The quantity and quality of microalgal lipids can be improved through the manipul ation of macronutrient concentration. Nitrogen deprivation and mixotrophic condition can increase the lipid content and affect the lipid composition of algae. Two-stage cultivation system has been recently proposed to reduce the negati ve impacts of nitrogen deficiency on biomass production. In this study, Tetraselmis sp. KY114885 was cultured in a F2 medium supplemented with 5 g/L of different organic carbon sources li ke glucose, glycerol, sodium acetate, sucrose and sorbitol under mixotrophic condition. Glucose increased the biomass concentration 1.3 times m ore than the control group, and the highest lipid yield (400.00 ± 17.32 mg/L) and lipid content (16.57 ± 0.08%) were achieved in the presen ce of glucose. At the next step, the effects of different nitrogen concentrations on biomass pr oduction and lipid profile of Tetraselmis sp. KY 114885, were evaluated.using a two-stage culti vation system. After 8 days of mixotrophic cultivation in a F2 medium with 5 g/L glucose, the harrvested biomass was transferred to a new media c ontaining different nitrate concentrations (0.88, 0.44, 0.22 and 0 mM) and cultured autotrophic ally. The algae growth was monitored until the 20th day after inoculation. The algal lipids harve sted after 12 and 20 days were converted to f atty acid methyl esters by direct transesterification and characterized using GC-FID chromatography. Statistical analysis was performed usi ng SPSS software and means of value were com pared by Tukey test at the confidence level of 95 %. The biomass yield in cultures with 0. 88 mM nitrogen was 1.20, 1.52 and 1.83 times m ore than the cultures containing 0.44, 0.22 and 0 mM nitrogen. On the contrary, the fatty acid pr ofile was not significantly affected by nitrogen level and incubation time. The percentage of m ain fatty acids such as C16:0, C16:1, C18:0, C18:1n9c and sum of saturated, monounsaturated and polyunsaturated fatty acids did not change. Monounsaturated and polyunsaturated fatty acids were the highest and lowest part of algal lipids, respectively. The results suggest that nitrogen limita tion can not be applied as an effective approach to modify lipid profile and biodesel quality of Tetraselmis sp. KY114885.