Green factories: The shaping and use of metabolic pathways in algae

The complex endosymbiotic history of algal plastids has generated a high degree of diversity within their metabolic pathways. The shaping and merging of pathways from various combinations of hosts and endosymbionts is responsible for important biochemical innovations such as those exemplified by the emergence of starch metabolism. Green algae, such as Chlamydomonas reinhardtii, contain an oxygen-sensitive high-specific-activity hydrogenase that, in special circumstances, can generate molecular hydrogen directly from photosynthesis, or indirectly through the storage of photosynthetic energy in starch. The challenge now facing biochemists studying these pathways is to make use of these organisms to produce molecular hydrogen in a sustainable and efficient fashion.