Effects Of Environmental Factors On The Growth And Fatty Acids Composition Of Isochrysis Galbana

Isochrysis galbana belongs to chrysophyta, chrysophyceae, Isochrysidales, Isochrysidaceae, Isochrysis Parke. It's a kind of single microalgae, which has no cytoderm. Isochrysis galbana is photoautotrophic, and contains much fatty acids.The growth and fatty acids composition can be affected by several environmental factors. Isochrysis galbana is cultured in batch under various conditions and it's growth and fatty acids content are investigated. Within the experimental range, the cell concentration and specific growth rate increase with increasing concentrations of NaNO₃ and NaH₂PO₄. The lower concention of NaNO₃ and NaH₂PO₄ can hasten the accumulation of fatty acids in microalgae cells, while it can get high content of DHA when NaNO₃ and NaH₂PO₄ are sufficient. The cell concentration, fatty acids content and output reach the maximum values of 1020×10⁴/mL, 38.26% and 94.42mg/L at pH 8.0, while the maximum content of DHA in total fatty acids and in dry weight are achieved at pH 7.5, which are 10.02% and 3.53%, but the output of DHA gets maximum at pH 8.0, which is 8.99mg/L. The cell concentration and DHA output will be high under the suitable illumination and aeration, but that will decrease when illumination and aeration are too high or too low. And DHA content in total fatty acids increases as illumination and aeration increase.The semi-continuous culture of I. galbana is conducted by columned and flat photoreactors in order to achieve I. galbana high concentration culture. Renewal rate and renewal period affect the cell and DHA productivity markedly. The cell productivity reaches the maximum under the conditions of 11.5mg/L NO₃^--N concentration, 1.1mg/L PO₄^3--P concentration, 0.20 renewal rate, 1d renewal period, which is 0.3786g/L, and when the condition is 11.5mg/L NO₃^--N concentration, 0.7mg/L PO₄^3--P concentration, 0.20 renewal rate and 1d renewal period, DHA productivity is maximum, 7.707mg/(L·d). Fed-batch culture is more suitable to the growth of I, galbana than single batch culture, and increased feeding is better than continuous feeding. The cell concentration gets maximum when the increased feeding factor K is 0.100, as the feeding quantity is 3.6L. But the DHA content in total fatty acids also increases while feeding quantity dereases straightly.