光敏色素基因cikA对光暗循环培养条件下高产糖聚球藻UTEX2973糖代谢影响研究

聚球藻UTEX2973（Syn2973）是目前发现生长速度最快的蓝细菌。正常培养条件下，野生型藻株胞内可积累51%干重的糖原。盐胁迫条件下，项目组前期构建的蔗糖高产突变株Syn2973∷CscB蔗糖产率不仅达到35.5mgL−1h−1，还可积累与野生型相近的胞内糖原。以上数据均在持续光照条件下获得，藻株在产糖应用中不可避免要面对自然光（光暗循环）培养，光暗循环对藻株糖代谢影响尚不清楚。同时，光敏色素CikA是控制光暗循环信号输入的关键调控因子，该调控因子对藻株光暗循环下糖代谢的影响机制也不明确。为了解决上述两个问题，本项目首先研究光暗循环对Syn2973糖合成及糖代谢关键基因的转录及蛋白表达的影响；其次，控制cikA表达，解析光暗循环下cikA对Syn2973糖代谢的影响机制。本研究将为光暗循环对糖合成的调控机制提供重要信息，对于建立新型糖原料合成路线奠定基础，具有重要的理论实践意义。

Synechococcus elongatus UTEX 2973 is the fastest growing cyanobacterium reported so far. Under nitrogen-replete (normal) condition, wild type Syn2973 could accumulate glycogen with a content as high as 51 % of the dry cell weight (DCW) at the stationary phase. Under salt stress condition, the highest extracellular sucrose productivity reached 35.5 mg L−1 h−1 for the Syn2973 strain expressing cscB, which contained the similar amount of intracellular glycogen with the wild type. However, the results were acquired under continuous illumination conditions, the sun-light (light-dark cycle, LD) condition is inevitable for the process of the cyanobacterial sugar application, and the effect of the LD condition on the Syn 2973 sugar metabolism is not yet clear. Meanwhile, phytochrome CikA is the main LD signal input factor of the circadian system, and the regulatory mechanism of which on the sugar metabolism under LD condition is also undefined. To solve the above two problems, in this project, the effects of LD condition on the sugar synthesis, the sugar metabolic genes transcription levels and the expression of the related proteins to the sugar metabolism will be firstly studied. Then, the mechanism of the effect of cikA gene on the sugar metabolism under LD condition in Syn 2973 will be analyzed. This study will provide basic information for regulatory mechanism of sugar metabolism in Syn 2973 under the LD condition, and set a substantial basis for developing a novel sugar synthesis route.