Assessing the potential of sucrose production by genetically engineered cyanobacteria

与利用化石资源相比，利用光合生物的可再生生物质生产生物燃料和生化物质几乎是二氧化碳中性的过程。像蓝藻这样的光合生物将能量储存在高分子量和低分子量的糖中，这些糖可以通过微生物发酵或化学催化转化为燃料或化学原料。由于蓝藻是一种光合作用的快速生长的微生物，可以在特定条件下积累蔗糖，因此它们有可能作为可再生燃料和化学品的生物质衍生产品的糖源。两位申请者在理解糖合成的分子机制（德国方面）及其在可溶性糖生产中的应用方面有共同的兴趣（中国合作伙伴用蓝藻实现了5-6 mg蔗糖L-1 h-1的速率）。虽然蓝藻蔗糖的生产潜力很大，但要实现工业规模应用，还需要增加蔗糖的产量。由于蔗糖生物合成的调控机制尚不清楚，且蔗糖的合成和分泌效率较低，限制了这种尝试。为了提高蔗糖的产量，我们提出了以下研究任务：通过蓝藻代谢工程优化基因表达，提高蔗糖的生物合成效率；破坏竞争途径，将碳通量重定向到蔗糖生物合成途径；筛选和表达不同来源的蔗糖转运蛋白，提高蔗糖的分泌效率。蔗糖合成酶在转录和生化水平上的调控研究，比较不同来源生物的酶和基因。研究能提高蔗糖产量的条件（盐、二氧化碳的可用性）。

The production of biofuels and biochemicals from renewable biomass of photosynthetic organisms results in an almost CO2-neutral process compared to utilizing fossil resources. Photosynthetic organisms such as cyanobacteria store their energy in high and low molecular mass sugars, which can be converted into fuels or chemical feedstock through microbial fermentation or chemical catalysis. Because cyanobacteria are photosynthetic, fast-growing microorganisms that can accumulate sucrose under specific conditions, they have a potential application as a sugar source for the biomass-derived production of renewable fuels and chemicals. The two applicants have mutual interests in the understanding of molecular mechanisms of sugar synthesis (German side) and its application for soluble sugar production (a rate of 5-6 mg sucrose L-1 h-1 was achieved with cyanobacteria by the Chinese partner). Although it is clear that cyanobacterial sucrose production has great potential, for the industrial scale application the sucrose production needs to be increased. Such attempts are limited by the unknown regulatory mechanism of sucrose biosynthesis as well as the low sucrose synthesis and secretion efficiency. To improve sucrose production, we propose the following research tasks: Metabolic engineering of cyanobacteria to optimize the expression of genes for enhancing the sucrose biosynthesis efficiency; to disrupt the competitive pathway for redirecting the carbon flux into sucrose biosynthesis pathway; to screen and express the sucrose transporters with different origins for improving the sucrose secretion efficiency. Study of the regulation of sucrose biosynthesis enzymes on transcriptional and biochemical level comparing enzymes and genes from different source organisms.Investigating conditions (salt, CO2 availability) which will improve sucrose production.