Toyoshima Masakazu, Mori Natsumi, Moriyama Takashi, Misumi Osami, Sato Naoki
Department of Life Sciences, Graduate School of Arts and Science, The University of Tokyo,Tokyo,Japan.
Core Research for Evolutional Science and Technology, Japan Science and Technology Agency,Tokyo,Japan.
Microbiology (Reading). 2016 May;162(5):803-812. doi: 10.1099/mic.0.000261. Epub 2016 Feb 29.
Triacylglycerol (TAG) produced by microalgae is a potential source of biofuel. Although various metabolic pathways in TAG synthesis have been identified in land plants, the pathway of TAG synthesis in microalgae remains to be clarified. The unicellular rhodophyte Cyanidioschyzon merolae has unique properties as a producer of biofuel because of easy culture and feasibility of genetic engineering. Additionally, it is useful in the investigation of the pathway of TAG synthesis, because all of the nuclear, mitochondrial and plastid genomes have been completely sequenced. We found that this alga accumulated TAG under nitrogen deprivation. Curiously, the amount and composition of plastid membrane lipids did not change significantly, whereas the amount of endoplasmic reticulum (ER) lipids increased with considerable changes in fatty acid composition. The nitrogen deprivation did not decrease photosynthetic oxygen evolution per chlorophyll significantly, while phycobilisomes were degraded preferentially. These results suggest that the synthesis of fatty acids is maintained in the plastid, which is used for the synthesis of TAG in the ER. The accumulated TAG contained mainly 18 : 2(9,12) at the C-2 position, which could be derived from phosphatidylcholine, which also contains this acid at the C-2 position.
微藻产生的三酰甘油（TAG）是一种潜在的生物燃料来源。尽管陆地植物中已鉴定出TAG合成的各种代谢途径，但微藻中TAG的合成途径仍有待阐明。单细胞红藻梅氏嗜热栖热菌作为生物燃料生产者具有独特的特性，因为其易于培养且具备基因工程可行性。此外，由于其核基因组、线粒体基因组和质体基因组均已完全测序，它在TAG合成途径的研究中很有用。我们发现这种藻类在氮缺乏条件下积累TAG。奇怪的是，质体膜脂的数量和组成没有显著变化，而内质网（ER）脂的数量增加，脂肪酸组成发生了相当大的变化。氮缺乏并没有显著降低每叶绿素的光合放氧量，而藻胆体优先降解。这些结果表明，质体中脂肪酸的合成得以维持，用于在内质网中合成TAG。积累的TAG在C-2位置主要含有18 : 2(9,12)，这可能来源于磷脂酰胆碱，其在C-2位置也含有这种酸。
