不同氮源及氮浓度对真眼点藻纲微藻生长及油脂积累的影响

以真眼点藻纲8株微藻(类波氏真眼点藻(Eustigmatos cf. polyphem)、大真眼点藻(Eustigmatos magnus)、波氏真眼点藻(Eustigmatos polyphem)、魏氏真眼点藻(Eustigmatos vischeri)、斧形魏氏藻(Vischeria helvetica)、点状魏氏藻(Vischeria punctata)、星形魏氏藻(Vischeria stellata)和眼点拟微绿球藻(Nan-nochloropsis oculata))为研究材料, 用3种氮源(硝酸钠、碳酸氢铵或尿素)和4种氮浓度(18、9、6和3 mmol) 在改良的BG-11培养基中对藻细胞进行培养。比较分析这8株微藻在不同培养条件下的藻液pH、生物量、油脂含量、脂肪酸组成的差异, 从而筛选出适合该类微藻生长和油脂积累的最适氮源与最佳氮浓度。结果表明, 这8株微藻均能在3种氮源中生长, 但是随着培养时间延长, 以碳酸氢铵和尿素为氮源时藻液pH逐渐降低, 其变化范围为5.0—6.0, 而以硝酸钠为氮源时藻液pH保持在7.0—8.0, 变化不大。当以尿素为氮源培养时, 能获得较高的生物量, 但是不同藻株在不同尿素浓度时达到最高生物量。最高生物量是波氏真眼点藻(E. polyphem)在9 mmol时达到, 为10.96 g/L。总脂含量分析发现, 在低氮浓度下均能促进8株微藻油脂的积累, 真眼点藻属中的魏氏真眼点藻(E. vischeri)在8株藻中获得最高油脂含量, 达到59.24%。进一步对脂肪酸分析发现, 8株微藻总脂肪酸含量为细胞干重的50%—58%, 主要脂肪酸组成为豆蔻酸(C14鲶0)、棕榈酸(C16鲶0)、棕榈油酸(C16鲶1)、油酸(C18鲶1)和二十碳五烯酸(C20鲶5), 其中拟微绿球藻(N. oculata)细胞中棕榈酸的含量最高占总脂肪酸50%左右; 其他7株微藻细胞中棕榈油酸的含量较高, 其占总脂肪酸含量范围在40%—60%。8株微藻均表现出较高的生物量与油脂积累能力, 以尿素为氮源, 氮浓度为6 mmol时更有利于该类微藻生物量和油脂的积累。总体来说, 真眼点藻纲的微藻是一类极具潜力适合于微藻生物燃料生产的微藻, 而真眼点藻属藻株表现更为明显的优势。

EFFECTS OF DIFFERENT NITROGEN SOURCE AND CONCENTRATION SUPPLIES ON THE GROWTH AND LIPID ACCUMULATION OF EUSTGMATOPHYCEAN MICROALGAE

To investigate the effects of nitrogen on the growth and lipids accumulation of Eustgmatophyceae, three dif-ferent nitrogen sources (sodium nitrate, ammonium bicarbonate and urea) and four different initial nitrogen concentra-tions (18 mmol, 9 mmol, 6 mmol and 3 mmol) were used to culture eight species of Eustgmatophyceae (Eustigmatos cf. polyphem,Eustigmatos magnus,Eustigmatos polyphem,Eustigmatos vischeri,Vischeria helvetica,Vischeria punctata, Vischeria stellata andNannochloropsis oculata) to select the best culture condition. The pH values of culture medium, biomass, lipids accumulation and fatty acid composition of Eustgmatophyceae were utilized to assess its effects. The results showed that three kinds of nitrogen sources were suitable for the eight species. For the prolong culture, the pH values of culture medium gradually reduced to 5.0—6.0 when ammonium bicarbonate and urea were used as nitrogen sources, and the pH values of culture medium remained at 7.0—8.0 when sodium nitrate was used as nitrogen sources. Meanwhile, the higher biomass could be obtained when urea was used as nitrogen source, but different species reached to the highest biomass under different nitrogen concentrations. The highest biomass of 10.96 g/L was achieved inE. Polyphem at 9 mmol. Low nitrogen level could stimulate the lipids accumulation in all species with the highest lipid content of 59.24% of dry weight inE. vischeri. The total fatty acid contents of the eight species were about 50%—58%of dry weight, and the mainly fatty acids were myristic acid (C14:0), palmic acid (C16:0), palmitoleic acid (C16:1), oleic acid (C18:1) and eicosapentaenoic (C20:5). InN. oculata, the content of palmic acid was the highest one, which was about 50% of total fatty acids. However, in other seven species, the content of palmitoleic acid reached about 40%—60% of total fatty acids. In conclusion, urea (at 6 mmol nitrogen concentrations) is the best condition for the eu-stigmatophycean microalgae to accumulate biomass and oil. In general, all eight species of Eustgmatophyceae can ac-cumulate large contents of lipids, andEustigmatos showed the best potential to produce biofuels.