Genome sequencing of cyanobacterial endosymbiont of Rhopalodia gibberula. cyanobacterium endosymbiont of Rhopalodia gibberula

Diatom species of family Rhopalodiaceae possess cyanobacterial endosymbiont called "spheroid body" as well as plastids. Spheroid bodies are specialized for nitrogen-fixation and completely lack their photosynthetic ability. This cyanobacteria-derived symbiont is considered to be highly integrated into the host diatom cell, but the fact that the spheroid body appears only among rhopalodiacean diatoms suggests that acquisition of the spheroid body was quite recent compared to plastids. Thus the spheroid body is considered to exhibit an intermediate stage of transition from an endosymbiotic cyanobacterium to an organelle. In this project we sequenced the complete genome of a spheroid body of a rhopalodiacean diatom species, Rhopalodia gibberula. Comparative analysis with spheroid body genomes from other Rhopalodiacean diatom species would provide insights into genomic diversification and recent evolution of the cyanobacterial endosymbionts.