Triacylglycerol synthesis in cyanobacteria

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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.