Prevalence and molecular diversity of Archaea in subgingival pockets of periodontitis patients

Introduction: The aim of this study was to investigate the prevalence and molecular diversity of Archaea in the subgingival crevices of patients with chronic periodontitis. Methods: Subgingival plaque was collected from 41 patients with chronic periodontitis and 15 healthy subjects. The prevalence of Archaea in those plaque samples was tested by polymerase chain reaction with two broad-range archaeal primer sets. Amplicons from eight Archaea-positive plaque samples were cloned and sequenced for molecular diversity analysis using one of these two primer sets and a novel third primer set. Results: Archaea were detected in the subgingival plaque of patients with chronic periodontitis at a prevalence of 70.7-73.2%, but were not detected in healthy subjects. Using one primer set, all sequences of the archaeal amplicons were identified as Methanobrevibacter oralis-like species. With another primer set, the amplicons were also found to be identical to the uncultured M. oralis-like species except one phylotype was found to belong to the class Thermoplasmata. Conclusion: Archaea might be correlated with periodontal diseases. The diversity of Archaea associated with periodontitis was limited. Almost all sequenced amplicons fell into the genus Methanobrevibacter of the Euryarcheota phylum. M. oralis-like species was the predominant but non-exclusive archaeon in the subgingival dental plaque of patients with periodontitis.