Project description:The industrial feasibility of photosynthetic bioproduction using cyanobacterial platforms remains challenging due to insufficient yields, particularly due to competition between product formation and cellular carbon demands. Here we demonstrate that circadian regulation impacts carbon partitioning between storage, growth, and product synthesis in Synechococcus elongatus PCC 7942, significantly affecting production efficiency. After entrainment to light-dark cycles, cultures maintained under the constant light revealed distinct temporal patterns in sucrose production, exhibiting three-fold higher productivity during subjective night despite moderate down-regulation of the photosynthetic apparatus. This enhanced productivity coincided with reduced glycogen accumulation and halted cell division, suggesting temporal separation of competing processes. Transcriptome analysis revealed coordinated circadian-driven adjustment of the cell cycle and rewiring of energy and carbon metabolism. The subjective night was characterized by altered expression of cell division-related genes and reduced expression of genes involved in glycogen synthesis, while showing upregulation of glycogen degradation pathways, alternative electron flow components, the pentose phosphate pathway, and oxidative decarboxylation of pyruvate. These molecular changes created favorable conditions for product formation through enhanced availability of major sucrose precursors (glucose-1-phosphate and fructose-6-phosphate) and maintained redox balance. Our findings suggest that understanding the circadian regulatory rewiring of carbon metabolism could enable two distinct approaches for improving cyanobacterial bioproduction. First, accounting and leveraging natural circadian rhythms for optimizing cultivation conditions, timing of heterologous pathway induction and harvesting patterns. Second, engineering strains that mimic circadian-driven metabolic shifts through controlled carbon flux redistribution and redox rebalancing to enable efficient cycling between growth, storage accumulation, and production phases.
Project description:Circadian input kinas A (cikA) null cells severly distorts the genome-wide output of the circadian clock Synechococcus cultures (both wildtype and M-NM-^TcikA null cells) were synchronized with two light-dark (12h:12h) cycle before release into continuous light. Samples were collected at 4 h intervals for the next 24 h, total RNA was isolated from samples collected at each time points and genome-wide expression was measured using custom-designed microarrays
Project description:In this study, through computational modeling and synthetic biology tools, we identified and overcame a key flux controlling node in MEP-derived terpene biosynthesis in cyanobacteria. This strategy bypasses the limitation in traditional stepwise metabolic engineering, and led to significantly higher terpene productivity. Moreover, our results revealed photosynthesis limitations during high level of terpene production. We suggest that fine-tuning energy and reductant requirement could be a key factor in establishing a viable ‘non-native’ terpene sink in photosynthetic systems.
