Novel lipid accumulation pattern in a filamentous oleaginous microalga Tribonema utriculosum SAG22.94 under different initial nitrogen concentrations

We investigated the effects on growth, lipid content, and fatty acid profiles of Tribonema utriculosum SAG22.94 cultured under four different initial nitrogen concentrations (18.0, 3.0, 1.0, and 0 mmol/L). Results showed that the unbranched filaments were composed of cylindrical cells 9-15 μm wide and 17-29 μm long. The highest biomass concentration of T. utriculosum SAG22.94 cultured at a nitrogen concentration of 3.0 mmol/L was 6.39 g/L. The highest total lipid and total fatty acid contents were 44.62% and 42.21% of dry cell weight, respectively, when the filamentous microalgae were cultured under a nitrogen concentration of 18.0 mmol/L. The highest biomass and lipid and fatty acid productivities of 0.538, 0.209, and 0.206 g·L^-1·d^-1 were obtained under a nitrogen concentration of 3.0 mmol/L. Interestingly, total lipid and total fatty acid contents increased with the increase in nitrogen concentration within a certain threshold. In addition, the main fatty acid components of Tribonema utriculosum SAG22.94 were myristic acid (C14∶0), palmitic acid (C16∶0), palmitoleic acid (C16∶1ω7), arachidonic acid (C20∶4ω6), and eicosapentaenoic acid (C20∶5ω3, EPA). Among them, palmitoleic acid (C16∶1ω7) was the dominant fatty acid and accounted for 36.53%-50.08% of total fatty acids. In short, T.utriculosum SAG22.94 is a promising oleaginous filamentous microalga, with a unique lipid accumulation pattern.