Effects of Nutritional Factors on the Growth and Heterotrophic Eicosapentaenoic Acid Production of Diatom Nitzschia laevis

The effects of several nutritional factors on the growth and eicosapentaenoic acid （EPA） production of diatom Nitzschia laevis were studied. 4LDM （quadrupled concentration of the nutrient salt） was the optimal concentration of nutrient salt for the growth and EPA production ofN. laevis. The growth ofN. laevis was inhibited when the glucose concentration was either lower than 10gL^-1 or higher than 15 gL^-1. Both sodium nitrate and urea were good nitrogen sources for the growth and EPA production, while ammonium chloride seriously decreased the dry cell weight （DW） and the EPA content. Silicate seriously influenced the growth of N. laevis. The maximum DW of 2.34 gL^-1 was obtained in the presence of 150 mgL^-1 Na2SiO3· 9H2O. The EPA content remained almost the same when the silicate concentration was lower than 150mgL^-1; however, higher silicate concentrations resulted in a steady decrease of EPA content. Low medium salinity （≤29） did not seem to influence the DW of N. laevis, and high salinity resulted in a decrease of DW. The highest EPA content （4.08%） and yield （110mgL^-1） were observed at the salinity of 36 and 29, respectively. Key words polyunsaturated fatty acid; eicosapentaenoic acid; microalga; Nitzschia laevis; heterotrophy