高、低氮浓度对2株真眼点藻的生长和油脂积累的影响

【目的】研究氮浓度对真眼点藻纲(Eustigmatophyceae)的2株高产油微藻大真眼点藻(Eustigmatos magnus，EM)和波氏真眼点藻(Eustigmatos polyphem，EP)的细胞形态、生长、总脂含量、脂质组成和脂肪酸组成与含量的时序变化规律。【方法】利用高氮(18.0 mmol/L NO3?-N)和低氮(3.6 mmol/L NO3?-N)浓度培养微藻。【结果】形态观察结果表明，大真眼点藻(E. magnus)和波氏真眼点藻(E. polyphem)营养细胞具有1个周生的裂叶状叶绿体，细胞质中有液泡，内含能够振动的颗粒物，以及一个较为明显的红色色素体；生殖方式通过形成2个D形或4个四角形的似亲孢子；随着培养周期的延伸和营养盐的消耗，细胞中油体逐步形成，其数量不断增加，体积不断增大。实验结果表明，初始氮浓度对2种微藻的总脂积累及生长均有显著影响(P<0.05)，低氮浓度下2种微藻的生物质浓度分别为9.0 g/L和8.5 g/L，均低于高氮浓度下的生物质浓度。而低氮浓度下2种微藻的总脂、中性脂和总脂肪酸的含量以及总脂、中性脂与总脂肪酸的单位体积产率均明显高于高氮浓度组，其最高值分别为：59.10%、51.90%、46.95%和0.28、0.24、0.22 g/(L·d) (EM)；64.20%、56.80%、50.01%和0.32、0.28、0.25 g/(L·d) (EP)。脂肪酸分析结果表明，两种微藻的脂肪酸主要成分均为棕榈酸(C16:0)、棕榈油酸(C16:1)、油酸(C18:1)和二十碳五烯酸(C20:5，EPA)，四者的总含量(占总脂肪酸)分别达到85.83%和85.48%，其中棕榈油酸的含量最高。【结论】低氮浓度胁迫有利于大真眼点藻和波氏真眼点藻细胞内油脂的积累，两种微藻均为适合于生产生物柴油的油脂生产藻株。

Effects of high and low nitrogen concentration on the growth and lipids accumulation pattern of two oleaginous microalgae

Objective] To study the time-course changes in the cell morphology, growth, total lipid contents, lipid fractions and fatty acids profiles of Eustigmatos magnus and Eustigmatos polyphem (Eustigmatophyceae) under two different initial nitrate concentrations. Methods] The cultured concentration were 18.0 mmol/l (high nitrogen concentration) and 3.6 mmol/l (low nitrogen concentration). Results] The cell morphology and formation process of oil bodies of E. magnus and E. polyphem were also observed. The results showed that the vegetative cells of E. magnus and E. polyphem are usually oval to spherical. There are a single parietal, lobed chloroplast, conspicuous vacuoles, many vibrating granules and a large reddish pigment body in cytoplasm. The main reproduction way is by forming two D-shaped or four tetragonal autospores. The oil bodies emerged in cytoplasm along with cultivation time extending and nutrients exhausting. The initial nitrate concentration had a significantly influence on the growth and lipids accumulation of these two microalgae (P<0.05). The biomass concentrations of E. magnus and E. polyphem cultured under low nitrogen concentration were 9.0 g/L and 8.5 g/L, respectively, which were less than those gained at high nitrogen group. However, the higher contents and volumetric productivities of total lipids, neutral lipids and total fatty acids of these two microalgae were obtained at low nitrogen concentration. Their highest values reached 59.10%, 51.90%, 46.95%, 0.28 g/(L·d), 0.24 g/(L·d), 0.22 g/(L·d) (E. magnus); 64.20%, 56.80%, 56.80%, 0.32 g/(L·d), 0.28 g/(L·d), 0.25 g/(L·d) (E. polyphem), respectively. The fatty acids analysis indicated that the main fatty acids compositions of these two microalgae were palmitic acid, palmitoleic acid, oleic acid and eicosapentaenoic acid, which were up to 85.83% and 85.48% (of total fatty acids), respectively, among them, the content of palmitoleic acid was highest one. Conclusion] Low-nitrogen stress is conducive to storage lipids accumulation of E. magnus and E. polyphem, and both two microalgae are promising feedstock for biodiesel production.