脂肪烃生物合成在集胞藻PCC6803逆境胁迫应答中的作用研究

Aliphatic hydrocarbons are the predominant constituents of gasoline, diesel, and jet fuels, and they can be biosynthesized by a diversity of cyanobacteria. Cyanobacteria are widespread in all kinds of natural environments. As photosynthetic microbes, they can absorb solar energy and fix CO2 efficiently. Cyanobacteria become more and more attractive biofuel-producing systems because of their advantages over heterotrophic bacteria and plants. Synechocystis sp. PCC 6803 is a model cyanobacterium for basic and applied research. A two-step alkane biosynthetic pathway was identified in cyanobacteria recently，while physiological roles of aliphatic hydrocarbons in cyanobacteria are still unknown. Aliphatic hydrocarbons in Synechocystis sp. PCC 6803 were presumed to derive from acyl chains of membrane lipid according to previous study in our lab, and remarkable changes in constitute and content of aliphatic hydrocarbons were observed when Synechocystis sp. PCC 6803 responded to cold and salt stress. It opens a door to investigate the physiological role of aliphatic hydrocarbons in cyanobacteria. Studies will be focused on the following issues: 1. to track the metabolic profile of acyl chains in Synechocystis sp. PCC6803; 2. to determine transcription level of alkane biosynthetic genes under cold and salt stress; 3. to explore the causal relation between absence of aliphatic hydrocarbon biosynthesis and cell damage by accumulated free fatty acids. These studies will help to understand physiological roles of aliphatic hydrocarbons in microorganisms. Approaches and strategies will also be provided for improving aliphatic hydrocarbon production in cyanobacteria.

蓝细菌作为光能自养微生物能利用CO2作为唯一碳源, 且具有良好的环境适应性，是具有独特优势的能源生物系统。脂肪烃是汽油等液体燃料的主要成分。脂肪烃的生物合成在蓝细菌中广泛存在，其合成机理已得到鉴定，但是蓝细菌中脂肪烃的生理功能仍未见报道。 本项目前期研究结果显示，蓝细菌模式菌株集胞藻PCC6803中的脂肪烃可能来源于膜脂的脂酰基侧链，其组成和含量在低温和高盐等逆境胁迫条件下会发生显著变化。本项目将以此作为切入点开展以下研究：1. 膜脂脂酰基侧链的代谢流向分析；2. 低温、高盐条件下脂肪烃合成基因转录水平分析；3. 低温、高盐条件下脂肪烃合成基因缺失及互补突变株的生长情况、细胞通透性等表型分析和脂代谢分析。本项目致力于探究脂肪烃生物合成在集胞藻PCC6803逆境胁迫应答中的作用。该研究将为解析脂肪烃在微生物生理代谢过程中的作用和实现脂肪烃在蓝细菌中的高效合成提供借鉴。

脂肪烃在蓝细菌中广泛存在，其组成和含量相对保守。蓝细菌脂肪烃的生物合成途径已经得到鉴定，但生理功能尚不清楚。集胞藻PCC6803是蓝细菌模式菌株，其脂肪烃的主要成分为十七烷烃和十七烯烃。本项目选取集胞藻PCC6803作为主要研究对象，通过分析膜脂脂酰基侧链的代谢流向以及脂肪烃合成基因突变株在胁迫条件下的表型变化，发现集胞藻PCC6803的脂肪烃来源于膜脂中甘油脂sn-1位水解的脂酰基侧链；蓝细菌脂肪烃合成基因缺失突变株在低温下胞内积累游离脂肪酸，导致细胞受损、生长变差。.本项目揭示出脂肪烃生物合成在蓝细菌逆境胁迫应答中扮演着重要的角色。在低温、高盐等胁迫条件下，蓝细菌膜脂脂酰基侧链更新以及受损膜脂降解过程中均会释放出游离脂肪酸。通过将过量的游离脂肪酸转化为对细胞损伤较小的脂肪烃，蓝细菌将胞内游离脂肪酸含量维持在适当的水平，降低其对细胞造成的损伤。