Recent achievements in Synthetic Biology include in-yeast synthesis of whole bacterial genome from chemically synthesized oligonucleotides but also the cloning and engineering of natural whole bacterial genome and their subsequent back-transplantation in suitable recipient cells. These breakthroughs were performed with two related members of the class Mollicutes, and thenceforward their wide application depend on our future capacity to extend the transplantation technology to bacteria more signicant for biotechnology, agronomy or medicine. Toward that goal, our laboratory is currently focusing his attention in deciphering the molecular events that govern genome transplantation mechanisms. First, we evaluated the degree of relatedness necessary for a successful transplantation using Mycoplasma capricolum subsp. capricolum (Mcap) as a recipient cell and different genomes of more and more distant species, all belonging to the phylogenetic group Spiroplasma. A direct correlation between the transplantation effciency and the phylogenetic distance has been observed. These results clearly indicate that the phylogenetic distance between the donor cell and the recipient cell is a key parameter for GT. However, in certain cases, GT between closely related species was ine_cient revealing that some strain-species factors may also interfere during this process.We then established a transplantation limit for this system located between Mesoplasma florum and spiroplasmas genomes. This is of a great interest because, even if they are phylogenetically close, Mcap and M. orum are distinct species with a core proteome similarity of only ~89%. Using these two partners, we will now search for genetic factors responsible for GT incompatibility. Recently, promising results have been recorded using plasmids carrying optimized origin of replication (oriC) allowing a signi_cant increase in their transformation e_ciency in comparison to unmodifed oriC. This is the _rst evidence toward one main dream of genome transplantation, i.e. the optimization of donor genomes or recipient cells in order to create a more « universal » transplantation platform for bacterial species of interest.< Réduire