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

huxleyi Emiliania huxleyi是全球分布的单细胞钙化（白垩覆盖）微藻群的代表。赫胥黎双歧杆菌是海洋中数量最多的颗石藻，对海洋生态系统和全球碳、硫循环产生重大影响。大量的沿海和海洋中部的赫胥黎e.h huxleyi种群（被称为大量繁殖）经常突然消失，导致大量方解石流入海底，形成云的二甲基硫化物流入大气。赫胥黎衍生的脂质剖面被用作海洋表面温度在地质时间尺度上甚至短期季节时间尺度上变化的代理。过去对赫胥黎e.h huxleyi的研究已经产生了大量与地质历史、气候变化和进化相关的数据。随着全基因组序列的确定（即将发布）和基因操作工具的不断发展，这种历史兴趣和势头一直延续到基因组时代。赫胥黎大肠杆菌正迅速成为海洋世界的模型实验室菌株，如大肠杆菌和酿酒葡萄球菌。此外，最近发现的一种赫胥黎e.c hxleyi病毒具有影响脂质谱的天然能力，这表明该系统具有被操纵和以可控方式裂解的潜力。人们对赫胥黎菌感兴趣的历史原因（如其脂质含量和碳酸钙沉积特性）现在具有在后基因组未来开发的潜力。赫胥黎叶杆菌中最丰富的一些脂肪酸是omega-3多不饱和脂肪酸类的成员，作为一种营养保健品，对预防心血管疾病和人类健康的其他方面很重要，已经引起了相当大的兴趣。其他脂类也有用作生物燃料的潜力。从海藻中提取脂质并不是一个新想法，然而，在消费者意识日益提高的时代，必须考虑到与海藻生产有关的环境影响。这就是从球石藻中提取的脂质成为主要候选的地方：我们有机会开发一种新的系统来生产有用的产品，作为化学原料（生物燃料）和/或营养保健品（omega-3），同时也从碳循环中去除碳。该项目将在不久的将来调查赫胥黎系统的商业开发潜力。赫胥黎e.h huxleyi菌株的脂质谱将被广泛研究，以确定具有高商业价值的脂质（例如，omega-3 LC-PUFA二十二碳六烯酸），以及在合适的宿主系统中识别和表征其合成所涉及的基因。将这些途径转移到转基因植物的可能性也将被研究。另一个新的靶点将是C18高度不饱和的omega-3脂肪酸十八碳五烯酸（18:5,n-3）。这是一种特别丰富的omega-3脂肪酸，也是许多鱼油中一个次要但重要的成分。我们将首次确定这种脂肪酸在赫胥黎菌中的生物合成。病毒编码鞘脂生物合成途径的作用将被评估，特别强调新鞘脂产生的性质及其对细胞生理和裂解的影响。还将评估该病毒在脂质收集过程中使用的潜力。具体目标：1；深入表征赫胥黎杆菌菌株的脂质谱，以确定商业相关的脂质。2. 赫胥黎草脂质生物合成基因的鉴定与分子特征分析。3. 评估感染期间病毒编码鞘脂通路对赫胥黎假体脂质含量的影响及其对宿主生理和细胞破坏的影响。4. 通过在合适的宿主中异种表达赫胥黎大肠杆菌基因，评估高价值omega-3脂肪酸生产的潜力。

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.