Plasmids from bacterial endosymbionts of hump-killer paramecia.

Six isolates of Caedibacter taeniospiralis, collected from four continents, were screened for plasmid DNA. Plasmid DNA species containing between 41.5 and 49.5 kilobase pairs (kb) were observed in all strains. Physical maps of plasmids were constructed by determining relative positions of the restriction endonuclease (BamHI, SalI, XhoI, SacI, PstI, AvaI, and EcoRI) recognition sequences in each plasmid. The physical map of the smallest plasmid (41.5 kb), pKAP30, is reflected in each of the plasmids isolated from the other strains of C. taeniospiralis. Plasmid DNA from three of the isolates (strains 51 and 116 both from Indiana and strain 169 from Japan) each contain 43 kb, where 41.5 kb appear to be identical to pKAP30 (obtained from the Australian strain, A30). The extra 1.5 kb present in pKAP51, pKAP116, and pKAP169 is included as a single polynucleotide sequence. The 1.5-kb inclusion is located at apparently identical positions in pKAP116 and pKAP169 and at a totally different position in pKAP51. The two remaining plasmids, pKAP47 (from California strain 47) and pKAP298 (from Panama strain 298), both contain 49 kb to include a continuous 41.5-kb sequence that is apparently identical to pKAP30. The results indicate that the polynucleotide sequences of these plasmids are highly conserved and that the observed variations among them may be accounted for by transposable elements.