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Dynamic multiscale regulation of the central carbohydrate metabolism in cyanobacteria

Cyanobacteria are the ancestors of plant chloroplasts. They have significantly influenced life on our planet by combining two photosystems in photosynthesis, which has initiated the oxygenation of our atmosphere. The bioenergetics of cyanobacteria, as in algae and plants, is based on sunlight and photosynthesis. As prokaryotes, cyanobacteria have no compartments, except for carboxysomes, in which CO₂ fixation via Rubsico takes place. During a rotation of the Earth's axis, light conditions and thus the bioenergetic basis for cyanobacteria change periodically. Their central energy and carbohydrate metabolism therefore must change direction in a daily rhythm between day and night from photosynthesis and CO₂ fixation via the Calvin-Benson-Bassham (CBB) cycle to glucose oxidation and respiration. These processes are partly regulated by the circadian clock, which is well studied in cyanobacteria and consists of the three proteins KaiA, KaiB and KaiC. However, the metabolic bidirectionality is not limited to the day-night rhythm but is essential for fine-tuning and regulation at faster time scales also during the day. This is particularly challenging because, unlike in algae and plants, these processes in cyanobacteria share compartments, protein complexes and enzymes. The electron transport chains of photosynthesis and respiration are both localized in the thylakoid membrane, while CBB cycle and the degradation of carbohydrates take place side by side in the cytosol. This project focuses on multiscale fine-tuning of opposing processes in central carbohydrate metabolism in the cyanobacterium Synechoystis. We delete selected enzymes and characterize the mutants with respect to growth, electron transport in photosynthesis and respiration, CO₂ fixation, carbohydrate synthesis and degradation and investigate protein-protein interactions with the aim to understand the delicate network of dynamic processes in carbohydrate metabolism in detail.