The effects of trace elements on the lipid productivity and fatty acid composition of Nannochloropis oculata (N. oculata) were studied. The results showed that trace elements had a strong influence on not only the lipid productivity but also the fatty acid composition. The addition of Fe3+, Zn2+, Mn2+, Mo6+, and EDTA and the deletion of Cu2+ and Co2+ can increase the lipid productivity. The optimum concentrations of the trace elements in the culture medium are 6 times of Fe3+ and EDTA, the same concentration of Zn2+, Mn2+, and Mo6+ as the control group, but the optimum medium has no Cu2+ or Co2+. Fe3+, Zn2+, Mn2+, Mo6+, and EDTA are indispensable during the EPA formation of N. oculata. The addition of Fe3+, Zn2+, Mn2+, Mo6+, and EDTA can strongly increase the content of EPA in the lipid of N. oculata, but the concentration of the trace elements had little influence on the level of EPA. 1. Introduction In order to reduce the cost of biodiesel from microalgae, we can not only screen out the algal species that both grow well and have high lipid content but also explore the optimal culture condition to improve the lipid productivity of microalgae. N. oculata is a promising source of biodiesel because of its high growth rate and high lipid content, ranging from 31% to 68% [1]. Apart from the macroelements such as N, P, and C, the growth rate and lipid content of N. oculata can also be affected by trace elements. This is because trace elements are indispensable during the growing process of marine algae, and trace elements are indispensable parts of the algal cell itself and the enzyme active center of algal cell [2, 3]. There have been some reports about the effects of trace elements on the growth of microalgae. Liu and Wang [4] reported that high content of Fe3+ was beneficial to increase the lipid content of marine chlorella. Jeffrey and Millton [5] and Alexander and Markus [6] found that Mn2+ was indispensable during the growing process of microalgae and was the catalyst of photosynthesis and the activator of some kind of enzymes in microalgae. Yamochi [7] found that the addition of EDTA which could form a complex with many kinds of metal ions would promote the absorption of metal ions of microalgae and the growth of microalgae, and the complex iron was the inducement of red tide in the nutrition water. Boyer and Brand [8] found that trace elements could cause the abnormal propagation of microalgae, and suitable concentration of Fe3+, Mn2+, and Zn2+ could cause the mass rearing of microalgae. Yamasaki et al. [9] found that Mo6+ could control the growth
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