Comparison of two hypotheses for the evolution of plasmids in rickettsiae.

<p>(A) The appearance of a plasmid system in <i>R. felis</i> (as a member of SFG rickettsiae) as recently suggested (Ogata et al., 2005b; Blanc et al. 2007). (B) Our hypothesis centered on the notion that the ancestor to all rickettsiae harbored a plasmid system with subsequent losses in the ancestors to the TG and SFG rickettsiae, and in <i>R. canadensis</i> and <i>R. bellii</i> str. RML369-C. Red = ancestral rickettsiae, Aquamarine = typhus group, light blue = transitional group, brown = true spotted fever group. Trees are from <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0000266#pone-0000266-g002" target="_blank">Figure 2A</a>.