EFFECT OF DIFFERENT NITROGEN CONCENTRATIONS ON THE GROWTH PERFORMANCE AND PROXIMATE COMPOSITION OF Nannochloropsis sp.

Abstract

Microalgae are widely recognized in the aquaculture industries as a source of protein and in the oil industries as a source of biodiesel. Nannochloropsis is a promising source of protein and lipid due to its higher growth rate and cellular chemical compositions. Hence, the purpose was to determine the effect of nitrogen concentrations on cell growth and proximate composition of Nannochloropsis sp. For the experiment, Nannochloropsis sp. was grown in 100 g/L KNO3 present in Conway medium as the control and in 50 g/L, 75 g/L, 125 g/L, and 150 g/L KNO3 present in Conway medium respectively to determine stress effects. The culture volume was 1.5 L each. The results showed that the growth of Nannochloropsis sp., in terms of cell density and specific growth rate (SGR)was significantly (p < 0.05) higher (73.65 x 106) (0.772×106cells/day) at high concentration of KNO3 150g/L compared to other concentration 50g/L ( 21.93 × 106cells/ml; 0.451×106 cells/day), 75g/L ( 20.93 × ml x 106 cells/ml; 0.491×106 cells/day, 100g/L 29.03×106 cells/ml; 0.525×106 cells/day and 125 g/L 56.7 × 106 cells/ml; 0.739 ×106 cells/day) respectively. Protein content of Nannochloropsis sp. was significantly high (p < 0.05) at higher concentration of KNO3 (54 % dry weight) followed by 50 g/L (35 % dry weight), 75 g/L (41 % dry weight,) 125 g/L (48 % dry weight) and100 g/L KNO3 (47 % dry weight) respectively. On the other hand, lipid content (36% dry weight) was significantly higher (p < 0.05) at lower concentration of KNO3125g/L KNO3 to higher. In case of carbohydrate content there was no significant difference among the different stresses except the higher nitrogen stress (13% dry weight) of 150 g/L KNO3. Therefore, the effects of nitrogen concentration have an effective approach to acquire protein, lipid as well as higher cell density