Mycoplasma Laboratorium - Mycoplasma

Mycoplasma genitalium was chosen as it was the species with the smallest number of genes known at that time.

Mycoplasma is a genus of bacteria of the class Mollicutes in the division Tenericutes, characterised by the lack of a cell wall (making it Gram negative) due to their parasitic or commensal lifestyle (extracellular and intracellular). In molecular biology, the genus has received much attention. Apart from being a notorious and hard to eradicate (immune to beta-lactam and other antibiotics) contaminant in mammalian cell cultures, it has also been used as a model organism: the second published complete bacterial genome sequence was that of Mycoplasma genitalium, which has one of the smallest genomes of free-living organisms. The M. pneumoniae genome sequence was published soon afterward and was the first genome sequence determined by primer walking of a cosmid library instead of the whole-genome shotgun method. Consequently this species was chosen as a model for the minimal cell project, catalog the entire protein content of a cell.

Pelagibacter ubique (an α-proteobacterium of the order Rickettsiales) has the smallest known genome (1,308,759 base pairs) of any free living organism and is one of the smallest self-replicating cells known. It is possibly the most numerous bacterium in the world (perhaps 1028 individual cells) and, along with other members of the SAR11 clade, are estimated to make up between a quarter and a half of all bacterial or archaeal cells in the ocean. However, this species was identified only in 2002 by rRNA sequences and was fully sequenced in 2005, being an extremely hard to cultivate species which does not reach a high growth density, Additionally, several newly discovered species have fewer genes than M. genitalium, but many essential genes that are missing in Hodgkinia cicadicola, Sulcia muelleri, Baumannia cicadellinicola (symbionts of cicadas) and Carsonella ruddi (symbiote of hackberry petiole gall psyllid, Pachypsylla venusta) may be encoded in the host nucleus as these endosymbionts are acquiring an organelle-like status in a similar way to mitochondria and chloroplasts.