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ow nloaded from 2 ABSTRACT 20 The diversity of spirochetes in primary endodontic infections of teeth with 21 chronic apical periodontitis or acute apical abscesses was investigated using 22 16S rRNA gene clone library analysis. Prevalence of 3 common cultivable oral 23 Treponema species was also determined using species-specific nested 24 polymerase chain reaction (nPCR). All detected spirochetes belonged to the 25 genus Treponema. Overall, 28 different taxa were identified from the 431 clones 26 sequenced: 9 cultivable and validly named species, 1 cultivable as-yet-27 uncharaterized strain and 18 as-yet-uncultivated phylotypes, 17 of which were 28 novel. The large majority of clones (94%) were from cultivable named species. 29 The number of Treponema species/phylotypes per selected positive sample 30 ranged from 2 to 12. Species-specific nPCR detected T. denticola, T. socranskii 31 and T. maltophilum in 59 (66%), 33 (37%) and 26 (29%) of the 90 cases of 32 primary endodontic infections, respectively. Clone library analysis revealed 33 diverse Treponema species/phylotypes as part of the microbiota associated 34 with asymptomatic and symptomatic (abscess) endodontic infections. Although 35 several as-yet-uncultivated Treponema phylotypes were disclosed, including 36 novel taxa, cultivable named species were more abundant and frequently 37 detected. 3