"Candidatus Carsonella ruddii" is an obligate endosymbiotic Gammaproteobacterium[1] with one of the smallest genomes of any characterised bacteria.
It is therefore probably in the evolutionary process of becoming an organelle, similar to the mitochondria of eukaryotic cells that also evolved from an endosymbiont.
C. ruddii strain Pv (Carsonella-Pv) of the hackberry petiole gall psyllid, Pachypsylla venusta, was sequenced at RIKEN in Japan and the University of Arizona.
Numerous genes considered essential for life seem to be missing, suggesting that the species may have achieved organelle-like status.
[2] At the time of its sequencing, C. ruddii was thought to have the smallest genome of any characterized bacterial species.