Rewiring of Cyanobacterial Metabolism for Hydrogen Production: Synthetic Biology Approaches and Challenges.

With the demand for renewable energy growing, hydrogen (H-2) is becoming an attractive energy carrier. Developing H-2 production technologies with near-net zero carbon emissions is a major challenge for the "H-2 economy." Certain cyanobacteria inherently possess enzymes, nitrogenases, and bidirectional hydrogenases that are capable of H-2 evolution using sunlight, making them ideal cell factories for photocatalytic conversion of water to H-2. With the advances in synthetic biology, cyanobacteria are currently being developed as a "plug and play" chassis to produce H-2. This chapter describes the metabolic pathways involved and the theoretical limits to cyanobacterial H-2 production and summarizes the metabolic engineering technologies pursued.