Effects of nutrients and light intensity on the growth and biochemical composition of a marine microalga Odontella aurita

Algal biotechnology has advanced greatly in the past three decades.Many microalgae are now cultivated to produce bioactive substances.Odontella aurita is a marine diatom industrially cultured in outdoor open ponds and used for human nutrition.For the first time,we have systematically investigated the effects of culture conditions in cylindrical glass columns and flat-plate photobioreactors,including nutrients(nitrogen,phosphorus,silicon,and sulfur),light intensity and light path,on O.aurita cell growth and biochemical composition(protein,carbohydrate,β-1,3-glucan,lipids,and ash).The optimal medium for photoautotrophic cultivation of O.aurita contained 17.65 mmol/L nitrogen,1.09 mmol/L phosphorus,0.42 mmol/L silicon,and 24.51 mmol/L sulfur,yielding a maximum biomass production of 6.1–6.8 g/L and6.7–7.8 g/L under low and high light,respectively.Scale-up experiments were conducted with flat-plate photobioreactors using different light-paths,indicating that a short light path was more suitable for biomass production of O.aurita.Analyses of biochemical composition showed that protein content decreased while carbohydrate(mainly composed ofβ-1,3-glucan)increased remarkably to about 50%of dry weight during the entire culture period.The highest lipid content(19.7%of dry weight)was obtained under 0.11 mmol/L silicon and high light conditions at harvest time.Fatty acid profiles revealed that 80%were C14,C16,and C20,while arachidonic acid and eicosapentaenoic acid(EPA)accounted for 1.6%–5.6%and 9%–20%of total fatty acids,respectively.High biomass production and characteristic biochemical composition profiles make O.aurita a promising microalga for the production of bioactive components,such as EPA andβ-1,3-glucan.

硅藻金色奥杜藻色素的HPLC分析与超临界CO_2萃取研究

以硅藻金色奥杜藻(Odontella aurita)为实验材料,利用高效液相色谱法分析了其色素组成与含量,采取超临界CO2萃取技术研究了从干藻粉内提取岩藻黄素的条件。结果表明,该藻主要含有岩藻黄素、硅甲藻黄素、β-胡萝卜素、硅藻黄素等类胡萝卜素以及叶绿素a和叶绿素c1,其中岩藻黄素为该藻含量最高的类胡萝卜素。色素的萃取率与压强、温度、夹带剂含量以及萃取时间呈正相关,夹带剂含量对萃取率影响最大,CO2流速的影响最小;与有机溶剂法相比,超临界CO2萃取岩藻黄素效率略低,而更利于岩藻黄素的选择性萃取及分离提纯;岩藻黄素的SFE-CO2适宜条件为压强400 bar、温度50℃、CO2流速0.2 L/min、夹带剂比例10%、萃取时间2～3 h。

低氮对金色奥杜藻色素-蛋白复合物特性及全细胞蛋白表达的影响

采用SDS-PAGE圆盘电泳分离技术,研究两种氮浓度下17.6 mmol·L-1(高氮组)、5.87 mmol·L-1(低氮组)金色奥杜藻色素蛋白复合物的变化规律。结果表明,从两种氮浓度所培养的金色奥杜藻细胞光合膜上,均可分离得到6种色素蛋白复合物条带,按照迁移速率从小到大依次为CPⅠa、CPⅠ、CPa1、CPa2、LHCP1、LHCP2。与高氮组相比,低氮下电泳分离的复合物条带颜色明显变浅,尤其CPⅠ、CPa1、CPa2三条带仅隐约可见。低温荧光发射光谱显示CPa1的荧光发射主峰也较高氮组蓝移10 nm左右,说明低氮主要影响光系统Ⅱ。双向电泳和质谱分析结果表明,氮浓度降低后藻细胞中有6种蛋白表达下调,3种蛋白表达上调,这些差异蛋主要白涉及光合作用、氮素吸收、碳同化、能量转换等生理过程,大多与维持叶绿体功能有关。

不同缺氮营养水平对金色奥杜藻生长及光合生理的影响

采用了Φ6 cm柱状光生物反应器,在不同氮素营养条件(17.6 mmol/L N、8.8 mmol/L N、5.87 mmol/L N、0 mmol/L N)下通气培养硅藻金色奥杜藻[Odontella aurita(Bacillariophyceae;Centricae)],分析探讨藻细胞的光合生理及生长状况与氮素营养水平的关系。结果表明,不同氮素实验组藻细胞达到最大生长的时间明显差异,与对照组(17.6 mmol/L)相比,氮限制(5.87mmol/L N、8.8 mmol/L N)在培养的前期对金色奥杜藻的生长具有促进作用,氮饥饿(0 mmol/L)显著抑制藻细胞生长(P<0.05)。氮限制实验组藻细胞总碳水化合物的含量显著增加(P<0.05),而总蛋白含量明显下降(P<0.05)。藻细胞叶绿素a、c及总类胡萝卜素含量与培养液的氮素营养水平呈正相关。藻细胞最大光合放氧速率Pm随氮浓度下降而降低,呼吸速率Rd呈现相反趋势,PSⅡ最大光能转化效率(Fv/Fm)、实际光能转化效率(Yield)、潜在活性(Fv/Fo)以及相对电子传递效率(ETR)均随氮素限制而显著下降(P<0.05),说明藻细胞的表观光合生理状况与氮素营养水平直接相关。