Diversity and Morphology of Members of the Phylum Synergistetes in Periodontal Health and Disease

Members of the phylum Synergistetes have frequently been detected in the human oral cavity at sites of dental disease, but they have rarely been detected in studies of oral health. Only two oral Synergistetes taxa are cultivable. The aims of this study were to investigate the diversity of Synergistetes in the oral cavity, to establish whether Synergistetes taxa are more strongly associated with periodontitis than with oral health, and to visualize unculturable Synergistetes in situ. Sixty samples (saliva, dental plaque, and mucosal swabs) were collected from five subjects with periodontitis and five periodontally healthy controls. Using phylum-specific 16S rRNA gene primers, Synergistetes were identified by PCR, cloning, and sequencing of 48 clones per PCR-positive sample. Subgingival plaque samples were labeled with probes targeting rRNA of unculturable oral Synergistetes using fluorescent in situ hybridization (FISH). Analysis of 1,664 clones revealed 12 Synergistetes operational taxonomic units (OTUs) at the 99% sequence identity level, 5 of which were novel. Synergistetes OTU 4.2 was found in significantly more subjects with periodontitis than controls (P = 0.048) and was more abundant in subgingival plaque at diseased sites than at healthy sites in subjects with periodontitis (P = 0.019) or controls (P = 0.019). FISH analysis revealed that unculturable oral Synergistetes cells were large curved bacilli. The human oral cavity harbors a diverse population of Synergistetes. Synergistetes OTU 4.2 is associated with periodontitis and may have a pathogenic role.