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

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