A constrained SSU-rRNA phylogeny reveals the unsequenced diversity of photosynthetic Cyanobacteria (Oxyphotobacteria).

We show that only a little fraction of the oxyphotobacterial diversity has been sequenced so far. Indeed 31 rRNA clusters of the 60 composing the photosynthetic Cyanobacteria have a fraction of sequenced genomes < 1%. This fraction remains low (min = 1%, median = 11.1%, IQR = 7.3%) within the remaining "sequenced" clusters that already contain some representative genomes. The "unsequenced" clusters are scattered across the whole Oxyphotobacteria tree, at the exception of very basal clades. Yet, these clades still feature some (sub)clusters without any representative genome. This last result is especially important, as these basal clades are prime candidate for plastid emergence.