Methanogenic Archaea and human periodontal disease

Abstract

Archaea have been isolated from the human colon, vagina, and oral cavity, but have not been established as causes of human disease. In this study, we reveal a relationship between the severity of periodontal disease and the relative abundance of archaeal small subunit ribosomal RNA genes (SSU rDNA) in the subgingival crevice by using quantitative PCR. Furthermore, the relative abundance of archaeal small subunit rDNA decreased at treated sites in association with clinical improvement. Archaea were harbored by 36% of periodontitis patients and were restricted to subgingival sites with periodontal disease. The presence of archaeal cells at these sites was confirmed by fluorescent in situ hybridization. The archaeal community at diseased sites was dominated by a Methanobrevibacter oralis-like phylotype and a distinct Methanobrevibacter subpopulation related to archaea that inhabit the gut of numerous animals. We hypothesize that methanogens participate in syntrophic relationships in the subgingival crevice that promote colonization by secondary fermenters during periodontitis. Because they are potential alternative syntrophic partners, our finding of larger Treponema populations sites without archaea provides further support for this hypothesis.

Fig. 1.

Relative abundance of archaeal SSU rDNA, expressed as the mean percent of total prokaryotic SSU rDNA in Archaea-positive patients. Error bars represent standard error.

Fig. 2.

Mean bacterial (light gray) and archaeal (dark gray) rRNA gene copy number in periodontal health and disease. Gene copy number was determined by a quantitative 5′ nuclease assay. Error bars represent standard error.

Fig. 3.

Phylogenetic relationships of Archaea in the subgingival crevice inferred from SSU rDNA analysis. Phylotypes identified in this study are shown in bold. GenBank accession numbers for database sequences are given in parentheses except for M. ruminantium and M. arboriphilicus, which are only available from the Ribosomal Database Project (38). This dendrogram was constructed from 572 homologous sequence positions (349–957, E. coli numbering) using a maximum-likelihood algorithm.

Fig. 4.

Confocal micrographs of bacteria and archaea in subgingival plaque from a patient with severe periodontitis. (A) “Bright field” micrograph. (B) Fluorescent in situ hybridization micrograph of oral archaeum using SBGA-1 Cy-3-labeled polyprobe (pink) and counterstained with the nucleic acid dye YO-PRO-1 (blue).