Plasmids are abbreviated as follows: rsf10 (broad-host-range plasmid RSF1010), incPa (Broad host range plasmid Birmingham IncP α), escpl (enterohemorrhagic E. coli plasmid pO157), ype_1 (Yersinia pestis plasmid pMT-1), ype_2 (Y. pestis plasmid pCD1), ype_3 (Y. pestis plasmid pPCP1), agrTi (A. tumefaciens plasmid Ti), rhipl (Rhizobium plasmid pNGR234a), hpypl (H. pylori plasmid pHPM186); lacpl (L. lactis DPC3147 plasmid pMRC01), chlpl (virulence cluster from C. trachomatis plasmid pCHL1), aqupl (A. aeolicus plasmid ece1), halpl (Halobacterium sp. NRC-1 plasmid), mja_1 (M. jannaschii large plasmid), mja_2 (M. jannaschii small plasmid). See Fig. 2 for prokaryotic species abbreviations. Additional prokaryotes not included in Fig. 2 are salty (Salmonella typhimurium), yeren (Yersinia enterocolitica), yerpe (Yersinia pestis), serma (Serratia marcescens), vibch (Vibrio cholerae), and rhile (Rhizobium leguminosarum). Yellow background indicates δ* differences of a plasmid from its confirmed host. See also Fig. 6, which is published as supplemental data on the PNAS web site (www.pnas.org).