Reprogramming metabolic networks and manipulating circadian clocks for biotechnological applications

Cyanobacteria have two unique characteristics that distinguish them from all other prokaryotes - being able to perform oxygenic photosynthesis and having a circadian clock. Because cyanobacteria have a relatively simple genetic background and usually grow much faster than higher plants, they have become promising microbial hosts to produce biofuels and chemicals directly from sunlight and CO₂. Recent advances in synthetic biology and systems biology not only have provided impetus for reprogramming metabolic networks of cyanobacterial host cells, but also have greatly expanded our knowledge of the genetics, physiology, and regulatory mechanisms of cyanobacteria. The plasticity of cyanobacterial central metabolism allows researchers to reprogram the metabolic networks to enhance the production of chemicals, but the metabolic regulation that prevents maximizing chemical production is still poorly understood. The cyanobacterial circadian clock exerts global gene regulations and oscillates intracellular metabolism. Manipulation of the circadian clock genes has proven to be an effective strategy for modulating the expression patterns of both endogenous and exogenous genes, driving either constant up- or down-regulation, which might be leveraged to enhance the production of biofuels and chemicals in cyanobacteria.