Effect of high ferric ion concentrations on total lipids and lipid characteristics of Tetraselmis subcordiformis, Nannochloropsis oculata and Pavlova viridis

Microalgae as sources for biodiesel production have been widely investigated. Microalgae biomass, lipid content and fatty acid profiles of microalgae are limiting factors for the cost-effective production of biodiesel. In this paper, the effects of high ferric ion concentrations on three species of microalgae (Tetraselmis subcordiformis, Nannochloropsis oculata and Pavlova viridis) were studied. The microalgae were cultured in different concentrations (1.2 x 10(-2), 1.2 x 10(-1), 1.2 and 12 mmol L-1) of ferric ion. The growth, lipid content and fatty acid profiles of the three microalgae were analysed. When algae were cultured in 1.2 mmol L-1 ferric ion for 10 days, the final cell density and specific growth rates of T. subcordiformis, N. oculata and P. viridis decreased significantly (p < 0.05), and the total lipid contents of the microalgae, 33.72, 37.34 and 29.48 % (dry mass) in T. subcordiformis, N. oculata and P. viridis, respectively, were higher than those at other concentrations. The neutral lipid/total lipid ratios of the three microalgae species increased with increasing ferric ion concentration. Neutral lipids accounted for 50.75, 48.37 and 46.59 % of the total lipid in T. subcordiformis, N. oculata and P. viridis, respectively, when cultured in 12 mmol L-1 ferric ion. The proportions of saturated fatty acids in all three species cultured in 12 mmol L-1 ferric ion were significantly higher than those cultured in lower ferric ion concentrations. An optimum ferric ion concentration can improve the properties of T. subcordiformis, N. oculata and P. viridis as sources for biodiesel.