Huang Aiyou, Liu Lixia, Yang Chen, Wang Guangce
Institute of Oceanology, Chinese Academy of Sciences, Qingdao, 266071 China.
Institute of Plant Physiology and Ecology, Shanghai Institute for Biological Sciences, Chinese Academy of Sciences, Shanghai, 200032 China.
Biotechnol Biofuels. 2015 May 3;8:73. doi: 10.1186/s13068-015-0256-5. eCollection 2015.
Microalgae are potential sources of biofuels and high-value compounds. Mixotrophic conditions usually promote growth of microalgae. The pennate diatom Phaeodactylum tricornutum, with its short life cycle, completely sequenced genome, and ease of transformation, can be used as a model for studying carbon metabolism in microalgae.
We compared the growth rate of P. tricornutum (IOCAS-001) under different conditions and labeled the cells using [(13)C]glycerol (GL). The results revealed GL promoted the growth of P. tricornutum. Ser and Gly were synthesized via photorespiration. The (13)C enrichment of Ser and Gly under nitrogen-limited conditions was much higher compared to other amino acids, indicating the enhancement of photorespiration. Addition of sodium acetate decreased the growth rate of P. tricornutum under nitrogen-limited conditions. Our results indicated that the GL carbon backbone enters the Calvin cycle in the form of dihydroxyacetone phosphate (DHAP), producing xylulose 5-phosphate (X5P) with a GL2_3-generated carbon backbone distributed at X5P1_2 and ribose 5-phosphate (R5P) with GL1-derived carbon atoms at R5P1 and R5P2. Both R5P and X5P can be converted into ribulose-1,5-bisphosphate (RuBP). By oxygenation of RuBP carboxylase/oxygenase (Rubisco) and metabolism through photorespiration, these RuBPs generate Ser and Gly with GL1 or GL2-derived carbon atoms at position 1 and GL1 or GL3-derived carbon atoms at other positions, resulting in a low level of (13)C enrichment of Gly1 and Ser1.
Our results indicated different strains of P. tricornutum have different mechanisms for organic carbon metabolism. Photorespiration is involved in GL metabolism and is important for the nitrogen-limited response in P. tricornutum.
Metabolic flux analysis, microalgae.
微藻是生物燃料和高价值化合物的潜在来源。混合营养条件通常会促进微藻的生长。三角褐指藻是一种羽纹硅藻，具有生命周期短、基因组完全测序且易于转化的特点，可作为研究微藻碳代谢的模型。
我们比较了三角褐指藻（IOCAS - 001）在不同条件下的生长速率，并使用[(13)C]甘油（GL）对细胞进行标记。结果显示GL促进了三角褐指藻的生长。丝氨酸（Ser）和甘氨酸（Gly）通过光呼吸合成。与其他氨基酸相比，在氮限制条件下Ser和Gly的(13)C富集程度要高得多，这表明光呼吸增强。添加醋酸钠会降低三角褐指藻在氮限制条件下的生长速率。我们的结果表明，GL碳骨架以磷酸二羟丙酮（DHAP）的形式进入卡尔文循环，产生5 - 磷酸木酮糖（X5P），其中GL2_3生成的碳骨架分布在X5P1_2处，以及5 - 磷酸核糖（R5P），其R5P1和R5P2处带有GL1衍生的碳原子。R5P和X5P都可以转化为1,5 - 二磷酸核酮糖（RuBP）。通过RuBP羧化酶/加氧酶（Rubisco）的加氧作用以及光呼吸代谢，这些RuBP产生在位置1带有GL1或GL2衍生碳原子以及在其他位置带有GL1或GL3衍生碳原子的Ser和Gly，导致Gly1和Ser1的(13)C富集水平较低。
我们的结果表明不同菌株的三角褐指藻具有不同的有机碳代谢机制。光呼吸参与GL代谢，对三角褐指藻的氮限制响应很重要。
代谢通量分析，微藻
