Triacylglycerol synthesis in cyanobacteria

蓝细菌是进行类似于绿色藻类和植物的产氧光合作用的光合细菌。蓝细菌主要以糖原和聚羟基丁酸酯（PHB）的形式储存碳。蓝细菌是否能像在大多数真核细胞中发现的那样储存油（三酰甘油，TAG）的问题还不清楚。我们最近发现，模式蓝藻集胞藻PCC 6803含有一个酰基转移酶slr 2103，当在E.杆菌集胞藻Δ slr 2103的相应敲除突变体缺乏TAG和植基酯。蓝细菌TAG合成途径的发现为生长用于石油生产的蓝细菌细胞的生物技术应用打开了大门。集胞藻的聚油量极低。为了提高石油产量，我们将在集胞藻中过表达基因slr 2103。我们还将过表达脂肪酸活化酶（aas，fadD）以将更多酰基引入TAG合成。此外，我们将测量糖原（ΔglgC）或PHB（ΔphaCE）缺陷突变体中的TAG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，石油积累到更高的水平集胞藻和其他蓝藻。丝状蓝藻，如鱼腥藻或念珠藻，形成孢子（动孢子）。我们将测试在孢子形成过程中油是否积聚。我们还将研究嗜热蓝藻，费氏/Mastigocladus和Thermosynechococcus，在高温下生长过程中的石油积累。植物含有类似于slr 2103、PES 1和PES 2（植基酯合酶）的酰基转移酶。拟南芥pes 1 pes 2双突变体先前被证明是免费的植酯。我们将从集胞藻中引入slr 2103到pes 1 pes 2双突变体中并测试互补。这些实验将有助于理解蓝藻和植物中储存油合成的作用。它们将是潜在的开发高产油蓝藻生物技术应用的基础。

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.