Effect of trace elements on biomass, lipid productivity and fatty acid composition in Chlorella sorokiniana

The growth and lipid productivity of a freshwater microalga Chlorella sorokiniana Shihira et Krauss strain were investigated under different concentration combinations of ferric, manganous and zincic ions in photoheterotrophic culture. Low concentrations of Fe3+ (0, 0.001, 0.002 mmol L-1) promoted the growth of C. sorokiniana, while high concentrations (0.01 mmol L-1) restrained the algal growth. Fe3+ and Zn2+ increased lipid content of C. sorokiniana, while Mn2+ had less impact on lipid accumulation. The maximum lipid concentration per gram cellular weight of C. sorokiniana reached 64.91% on day 18. High concentration of Fe3+ (0.01 mmol L-1) increased significantly lipid productivity on day 12, which maximally reached 35.00 mg L-1, while Zn2+ and Mn2+ had less effect on lipid productivity at any stage. There was no significant difference of total sugar content among the different periods in the alga. In addition, 19 different fatty acids were identified in C. sorokiniana on day 18. Of these, palmitic acid and stearic acid were the most abundant fatty acid components, followed by linoleic acid. Ferric, manganous and zincic ions altered the proportion of saturated and unsaturated fatty acids of the same length of carbon chain, but could not vary its length or content. This strain of C. sorokiniana is a potential candidate as biodiesel feedstock.