BACKGROUND Oxygen-evolving photoautotrophic organisms, like cyanobacteria, protect their photosynthetic machinery by a number of regulatory mechanisms, including alternative electron transfer pathways. Despite the importance in modulating the electron flux distribution between the photosystems, alternative electron transfer routes may compete with the solar-driven production of CO2-derived target chemicals in biotechnological systems under development. This work focused on engineered cyanobacterial Synechocystis sp. PCC 6803 strains, to explore possibilities to rescue excited electrons that would normally be lost to molecular oxygen by an alternative acceptor flavodiiron protein Flv1/3-an enzyme that is natively associated with transfer of electrons from PSI to O2, as part of an acclimation strategy towards varying environmental conditions. RESULTS The effects of Flv1/3 inactivation by flv3 deletion were studied in respect to three alternative end-products, sucrose, polyhydroxybutyrate and glycogen, while the photosynthetic gas fluxes were monitored by Membrane Inlet Mass Spectrometry (MIMS) to acquire information on cellular carbon uptake, and the production and consumption of O2. The results demonstrated that a significant proportion of the excited electrons derived from photosynthetic water cleavage was lost to molecular oxygen via Flv1/3 in cells grown under high CO2, especially under high light intensities. In flv3 deletion strains these electrons could be re-routed to increase the relative metabolic flux towards the monitored target products, but the carbon distribution and the overall efficiency were determined by the light conditions and the genetic composition of the respective pathways. At the same time, the total photosynthetic capacity of the Δflv3 strains was systematically reduced, and accompanied by upregulation of oxidative glycolytic metabolism in respect to controls with the native Flv1/3 background. CONCLUSIONS The observed metabolic changes and respective production profiles were proposedly linked with the lack of Flv1/3-mediated electron transfer, and the associated decrease in the intracellular ATP/NADPH ratio, which is bound to affect the metabolic carbon partitioning in the flv3-deficient cells. While the deletion of flv3 could offer a strategy for enhancing the photosynthetic production of desired chemicals in cyanobacteria under specified conditions, the engineered target pathways have to be carefully selected to align with the intracellular redox balance of the cells.

中文翻译：

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重定向蓝藻Synechocystis sp。中的光合电子通量。PCC 6803通过缺失黄素二铁蛋白Flv3来实现。

背景技术像蓝细菌一样，放氧的光合自养生物通过多种调控机制，包括替代性电子转移途径，来保护其光合作用机制。尽管在调节光系统之间的电子通量分布方面很重要，但替代的电子传输路径可能会与正在开发的生物技术系统中由太阳驱动的CO2衍生的目标化学品的生产竞争。这项工作的重点是工程蓝细菌蓝藻属。PCC 6803菌株，旨在探索挽救通常由替代受体黄素二铁蛋白Flv1 / 3（通常与电子从PSI转移至O2的酶相关的酶）丢失到分子氧中的激发电子的可能性，作为适应策略的一部分应对不断变化的环境条件。结果针对三种替代终产物蔗糖，聚羟基丁酸酯和糖原研究了通过flv3缺失引起的Flv1 / 3失活的影响，同时通过膜入口质谱法（MIMS）监测了光合气体通量，以获取有关细胞碳吸收的信息。 ，以及O2的生产和消耗。结果表明，在高CO2尤其是高光强度下生长的细胞中，通过光合水裂解产生的大量激发电子通过Flv1 / 3丢失给分子氧。在flv3缺失菌株中，这些电子可以重新布线，以增加朝向被监测目标产物的相对代谢通量，但是碳的分布和整体效率是由光照条件和各个途径的遗传组成决定的。同时，Δflv3菌株的总光合作用能力被系统地降低，并伴有相对于具有天然Flv1 / 3背景的对照的氧化糖酵解代谢的上调。结论观察到的代谢变化和各自的生产概况被认为与缺乏Flv1 / 3介导的电子转移以及细胞内ATP / NADPH比值的降低有关，这必然会影响flv3缺陷型中的代谢碳分配。细胞。尽管flv3的缺失可以为在特定条件下增强蓝细菌中所需化学物质的光合作用产生提供策略，