Understanding the biosynthesis of omega-3 long chain polyunsaturates in emiliania huxleyi

Emiliania huxleyi is a representative of the cocolithophores, a group of unicellular calcifying (chalk-covered) microalgae with global distribution. E.huxleyi is the most numerous coccolithophore in our oceans and greatly impacts on marine ecosystems and on the global carbon and sulphur cycles. Vast coastal and mid-ocean populations (known as blooms) of E.huxleyi often disappear suddenly causing substantial fluxes of calcite to the seabed and cloud-forming dimethyl sulphide to the atmosphere. E.huxleyi-derived lipid profiles are used as a proxy for variations in sea surface temperature shifts over geological time scales and even short term seasonal time scales. The past study of E.huxleyi has produced a vast amount of data relevant to geological history, climate change and evolution. This historical interest and momentum has followed through to the genomic era with the determination of the full genome sequence (to be released shortly) and the ongoing development of genetic manipulation tools. E.huxleyi is rapidly becoming the marine world's equivalent of model laboratory strains such as E.coli and S. cerevisiae . Furthermore, the recent identification of an E.huxleyi virus with the natural ability to influence the lipid profile, suggests a system that has the potential to be manipulated and lysed in a controlled manner. The historical reasons for interest in E.huxleyi (such as its lipid content and calcium carbonate deposition properties) now have the potential for exploitation in the post-genomic future. Some of the most abundant fatty acids of E.huxleyi are members of the omega-3 polyunsaturate class, which has attracted considerable interest as a nutraceutical, important for the prevention of cardio-vascular disease and other aspects of human health. Other lipids have the potential for use as biofuels. Lipid extraction from marine algae is hardly a new idea, however, in an age of increasing consumer awareness the environmental implications associated with their production must be taken into consideration. This is where lipids derived from the coccolithophores become the leading candidates: we have the opportunity to develop a novel system to produce useful products, either as chemical feedstocks (bio-fuels) and/or nutraceuticals (omega-3s), whilst also removing carbon from the carbon cycle at the same time. This project will investigate the potential of the E.huxleyi system for commercial exploitation in the near future. The lipid profile of E.huxleyi strains will be studied extensively to identify lipids of high commercial interest (for example, the omega-3 LC-PUFA docosahexaenoic acid) and the genes involved in their synthesis identified and characterised in suitable host systems. The potential for transfer of the pathways to transgenic plant will also be investigated. Another novel target will be the C18 highly unsaturated omega-3 fatty acid octadecapentaenoic acid (18:5, n-3). This is a particularly abundant omega-3 fatty acid, and is also a minor yet significant component of many fish oils. We will for the first time define the biosynthesis of this fatty acid in E.huxleyi. The role of the virally encoded sphingolipid biosynthesis pathway will be assessed with particular emphasis on the nature of the novel sphingolipids produced and their effect on cellular physiology and lysis. The potential of the virus to be used in the lipid harvesting process will also be assessed. Specific objectives: 1. In depth characterisation of E.huxleyi strains' lipid profiles with a view to identifying commercially relevant lipids. 2. Identification and molecular characterisation of lipid biosynthesis genes in E.huxleyi. 3. Assess the impact of the virally encoded sphingolipid pathway on E.huxleyi lipid content during infection and its impact on host physiology and cellular disruption. 4. Evaluate the potential for high-value omega-3 fatty acids production via heterologous expression of E. huxleyi genes in a suitable host.