[61]. Their small size favors transfer mechanisms like transduction, natural transformation and co-integration in mobile elements. The topology of the rep phylogenetic tree (Figure 6) is not consistent with the idea of a common plasmid ancestor that would have been vertically inherited in both phytoplasma and mycoplasma clades. Moreover, the clear-cut clustering of mycoplasma plasmids into P5091 purchase separate branches supports the hypothesis of

several, rather than a single, mycoplasma plasmid ancestors. Using the clustering of rep sequences, we propose a new nomenclature system that applies to all currently described mycoplasma and phytoplasma plasmids. This classification does not take into account the plasmid host as these elements are transmissible Selleckchem SB-715992 from one species to another. As the spiroplasma plasmids do not carry a rep sequence showing a significant homology with those described here (Figure 6), they cannot be included in this nomenclature. While this paper was under review, Kent et al. published a study showing the use of pMyBK1 as a shuttle vector for heterologous gene expression in M. yeatsii[25]. We confirm that pMyBK1 represents a novel RCR plasmid family and that its derivatives

can be used as gene vectors to express cloned genes not only in M. yeatsii[25] but also in three other ruminant mycoplasmas. This result is not trivial Selleck SAR302503 in a group of organisms for which the genetic toolbox is very limited. The pMyBK1 plasmid has a small size, lacks any CDS homologous to genes for mating pair formation but encodes a relaxase belonging to the MobV class. These features argue for a mobilizable

rather than conjugative nature of the plasmid [25, 62]. The fact that pMyBK1 was only detected in M. yeatsii is inconsistent with the finding that it replicates in mycoplasma species other than M. yeatsii, at least Monoiodotyrosine when introduced experimentally. Two hypotheses would explain this apparent contradiction. One is that the transfer of pMyBK1 is a rare event and hence, the number of strains screened was not large enough to detect additional pMyBK1-related plasmids. The other is that pMyBK1 would not be transferred in vivo or would not be stably maintained once transferred. Acknowledgements This work was supported by grant ANR09MIE016 (MycXgene) from the French national funding research agency (ANR) to CC (PI), by INRA, Région Aquitaine and ENVT. We would like to thank Guillaume Bouyssou, Agnès Tricot and Céline Michard for technical help. We would also like to thank Laure Maigre who made the first observation of the extrachromosomal elements in Mcc and M. yeatsii strains, and Eilean Bertram for revising the manuscript. Electronic supplementary material Additional file 1: Table S1. Additional file 5.