Unlocking the potentials of cyanobacterial photosynthesis for directly converting carbon dioxide into glucose

Glucose is the most abundant monosaccharide, serving as an essential energy source for cells in all domains of life and as an important feedstock for the biorefinery industry. The plant-biomass-sugar route dominates the current glucose supply, while the direct conversion of carbon dioxide into glucose through photosynthesis is not well studied. Here, we show that the potential of Synechococcus elongatus PCC 7942 for photosynthetic glucose production can be unlocked by preventing native glucokinase activity. Knocking out two glucokinase genes causes an accumulation of glucose in the medium, which eventually leads to glucose secretion. Without heterologous catalysis or transportation genes, glucokinase deficiency and a spontaneous genomic mutation lead to a glucose secretion of approximately 1.5 g/L, which is further increased to about 5 g/L through metabolic and cultivation engineering. These findings underline cyanobacterial metabolic plasticity and demonstrate applications for direct photosynthetic production of glucose.