CHARACTERIZATION OF A 4.2-KB PLASMID ISOLATED FROM PERIODONTOPATHIC SPIROCHETES

Oral anaerobic treponemes are associated with active periodontal disea se and may comprise up to 57% of the microbiota in periodontal pockets . Four treponeme strains (designated U2a, U2b, U9b, and U9c) isolated from clinical cases were found to harbor a new 4.2-kb plasmid when pla smid DNA was extracted and purified employing the Qiagen Plasmid Kit. This plasmid differs from the smaller plasmids (2.0-, 2.6-, and 2.7-kb ) reported previously by others in Treponema denticola. The newly disc overed 4.2-kb plasmid was found to be the same in all four treponeme s trains by restriction endonuclease analysis. It is a circular plasmid since restriction with Pst I, Pvu II, Sma I, Xma I, Ava I or Bam HI pr oduced a single band of the same size. Bacterial strain U2b was shown to be Treponema socranskii and U9c to be T. denticola. The plasmid is designated ''pTS 1''. The presence of the same plas mid in different s pecies of the treponemes isolated from the same patient suggests the p ossibility of a naturally occurring genetic transfer system within the oral spirochetes or their ability to take up and maintain mobilizable plasmids.