Environmental effects on growth and biochemical composition of Nitzschia inconspicua Grunow

The effects of nitrate and silicate levels, and carbon source on growth, biochemical composition and fatty acid composition of Nitzschia inconspicua were investigated using batch cultures. Within the range of silicate levels supplied (8.8-176 mu M), no marked variations in growth trend, biochemical composition or fatty acid composition were shown. Biomass at stationary phase, ranging from 64-66 mg ash-free dry weight (AFDW) L(-1), and specific growth rate (mu) based on chlorophyll alpha (0.41-0.50 d(-1)) of the cultures grown within 0.3-3.0 mM NaNO3 were not significantly different. Cultures supplemented with glucose (0.1% w/v), acetate (0.1% w/v) or 5% CO2 attained higher biomass (85, 85, 97 mg AFDWL(-1)) than the control which was grown in synthetic seawater and agitated by magnetic stirring. Cells grown at <3.0 mM NaNO3 contained higher carbohydrate contents (14.8-21.5% AFDW) than those grown at 3.0 mM (4.0% AFDW). Lipid content increased at the expense of proteins in cells aerated with 5% CO2. The dominant fatty acids, 16:0 and 16:1, ranged from 35.7-45.0% and 36.4-45.4% total fatty acids (TFA), respectively, while the relative proportions of 20:4 (n-6) and 20:5 (n-3) ranged from 1.7-5.4% and 3.4-5.9% TFA respectively. Cultures aerated with 5% CO2 attained the highest biomass (97 mg AFDW L(-1)) and yield of 20:5 (n-3) (0.34 mg L(-1)).