Triacylglycerol synthesis in cyanobacteria

蓝藻是一种光合细菌，与绿藻和植物类似，可以进行含氧光合作用。蓝藻以糖原和聚羟基丁酸盐（PHB）的形式储存碳。蓝藻是否能像在大多数真核细胞中发现的那样储存油（三酰基甘油，TAG），这个问题还不清楚。我们最近发现，模型蓝藻聚囊菌PCC6803含有酰基转移酶slr2103，该酶在大肠杆菌中表达时能够合成TAG和蜡酯（植基酯）。相应的聚囊藻Δslr2103敲除突变体缺乏TAG和植基酯。蓝藻中TAG合成途径的发现为蓝藻细胞在石油生产中的生物技术应用打开了大门。聚囊藻的积油量极低。为了提高石油产量，我们将在聚囊藻中过表达slr2103基因。我们将进一步过表达脂肪酸激活酶（aas, fadD）来引导更多的酰基进入TAG合成。此外，我们将测量糖原（ΔglgC）或PHB （ΔphaCE）缺乏突变体中TAG的积累，以解决碳是否可以重定向到油合成的问题。我们的目标是寻找条件下的油积累到更高的水平在聚囊藻和其他蓝藻。丝状蓝藻，如水藻或褐藻，形成孢子（akinetes）。我们将测试油是否在孢子形成过程中积累。我们还将研究嗜热蓝藻、Fischerella/Mastigocladus和热聚球菌在高温下生长过程中的油积累。植物含有类似slr2103、PES1和PES2（植酯合成酶）的酰基转移酶。拟南芥pes1 - pes2双突变体先前被证明不含植基酯。我们将把Synechocystis的slr2103引入到pes1 - pes2双突变体中，并进行互补试验。这些实验将有助于了解储油合成在蓝藻和植物中的作用。它们将为生物技术应用的高产油蓝藻的潜在发展奠定基础。

Cyanobacteria are photosynthetic bacteria which perform oxygenic photosynthesis similar to green algae and plants. Cyanobacteria store carbon mostly in the form of glycogen and polyhydroxybutyrate (PHB). The question whether cyanobacteria can store oil (triacylglycerol, TAG), as found in most eukaryotic cells, was unclear. We recently showed that the model cyanobacterium Synechocystis PCC6803 contains an acyltransferase, slr2103, which is capable of synthesizing TAG and wax esters (phytyl esters) when expressed in E. coli. The corresponding knock-out mutant of Synechocystis Δslr2103 is deficient in TAG and phytyl esters. The discovery of the TAG synthesis pathway in cyanobacteria opens the door for biotechnological applications of growing cyanobacterial cells for oil production. The amount of oil accumulation in Synechocystis is extremely low. To enhance oil production, we will overexpress the gene slr2103 in Synechocystis. We will furthermore overexpress fatty acid activating enzymes (aas, fadD) to channel more acyl groups into TAG synthesis. In addition, we will measure TAG accumulation in mutants deficient in glycogen (ΔglgC) or PHB (ΔphaCE) to address the question whether carbon can be redirected to oil synthesis. We aim to search for conditions under which oil accumulates to higher levels in Synechocystis and other cyanobacteria. Filamentous cyanobacteria like Anabaena or Nostoc, form spores (akinetes). We will test whether oil accumulates during spore formation. We will also study thermophilic cyanobacteria, Fischerella/Mastigocladus and Thermosynechococcus, for oil accumulation during growth at high temperatures. Plants contain acyltransferases similar to slr2103, PES1 and PES2 (phytyl ester synthase). The Arabidopsis pes1 pes2 double mutant was previously shown to be free of phytyl esters. We will introduce slr2103 from Synechocystis into the pes1 pes2 double mutant and test for complementation. These experiments will help to understand the role of storage oil synthesis in cyanobacteria and plants. They will be the basis for the potential development of high-oil producing cyanobacteria for biotechnological applications.