Assessing the potential of sucrose production by genetically engineered cyanobacteria

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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.