In photosynthetic organisms, chlorophyll (Chl) and bacteriochlorophyll (BChl) are essential for harvesting light energy and transferring electrons. Oxygenic phototrophs such as plants and cyanobacteria utilize Chl molecules, whereas anoxygenic phototrophic bacteria mainly use BChl. A difference in the chemical structures between Chl and BChl occurs at the C7-8 position. Chl molecules have the C7=8 double bond, and in BChl biosynthesis, the double bond is reduced by the enzyme, chlorophyllide oxidoreductase. In other words, the reduction toward C7-8 single-bond formation corresponds to the conversion of chlorin to a bacteriochlorin ring. This conversion provides a large shift in the absorption wavelength by approximately 80 nm. In addition, we found a natural variant of chlorophyllide oxidoreductase that catalyzes the formation of the C-8 ethylidene group as well as C7-8 single bond, resulting in the larger red shift of wavelength by over 100 nm. The variant oxidoreductase causes the committed step toward BChl b and g biosynthesis. Chlorophyllide oxidoreductase and protochlorophyllide oxidoreductase are similar to nitrogenase in sequence and structure. Construction of a4 phylogenetic tree of nitrogenase-like enzyme family showed that the core subunits of these oxidoreductases arose through sequential gene duplications and form a functionally homogenous phylogenetic group. We analyzed phylogenetic trees of other pigment biosynthetic enzymes and bacterial genomes, and found a clear phylogenetic relationship between the domain Bacteria and photosynthesis. We also conclude that the last phototrophic common ancestor probably had simple pigment biosynthesis proteins including Mg-chelatase, (proto)chlorophyllide oxidoreductase, and (B)Chl synthase.