The "green" phylogenetic clade of Rieske/cytb complexes.

More than a decade ago, Heliobacteria were recognised to contain a Rieske/cytb complex in which the cytochrome b subunit is split into two separate proteins, a peculiar feature characteristic of the cyanobacterial and plastidic b (6) f complex. The common presence of RCI-type reaction centres further emphasise possible evolutionary links between Heliobacteria, Chlorobiaceae and Cyanobacteria. In this contribution, we further explore the evolutionary relationships among these three phototrophic lineages by both molecular phylogeny and consideration of phylogenetic marker traits of the superfamily of Rieske/cytb complexes. The combination of these two methods suggests the existence of a "green" clade involving many non-phototrophs in addition to the mentioned RCI-type photosynthetic organisms. Structural and functional idiosyncrasies are (re-)interpreted in the framework of evolutionary biology and more specifically evolutionary bioenergetics.