Effect of N:P ratio on growth and chemical composition of Nannochloropsis oculata and Tisochrysis lutea

摘要

The understanding of how nitrogen (N) to phosphorus (P) ratios regulate growth and chemical composition of algae is important to control the nutritional value of microalgae for industrial application. This study compared the impacts of N:P ratio manipulations on the growth, elements, lipid, fatty acids and protein contents of Tisochrysis lutea and Nannochloropsis oculata. F/2 medium was used as the basal formula to obtained six N:P ratios of 5:1, 10:1, 20:1, 30:1, 60:1 and 120:1 and tested on the algae species in triplicate. Growth rate was similar in both algal species across all N:P ratios, and the carbon content in T. lutea was higher than in N. oculata. However, the carbon contents were high in the N:P ratios of 5:1 and 120:1 and low from 10:1 to 60:1 N:P ratios for both T. lutea and N. oculata. There were no significant differences in cellular N and P, but the protein contents depended on algae species and were significantly affected by N:P ratios. The N:P ratio of 20:1 favoured algal growth and protein content, while the N:P ratio of 120:1 reduced algal growth and protein synthesis but increased lipid in both algae. The 20:1 N:P ratio favoured eicosapentaenoic acid (EPA) production in N. oculata and the 30:1 N:P ratio favours docosahexaenoic acid (DHA) production in T. lutea. This study indicates that N:P ratio manipulation is an effective strategy to change biochemical composition in algae and N or P limitation tends to lower polyunsaturated fatty acids (PUFA) contents in algae.