Deep Sequencing of a Recent Bacterium Found in the Human Oral Cavity

The human oral cavity harbors 500–700 species of bacteria, depending on many factors, including diet, hormone levels, health status and genetics. We know very little about most of these bacteria, but it has been reported that many of them have yet to be cultured. An uncultured bacterium currently has no isolated pure culture, an example of such bacterium is Saccharibacteria. Candidatus Sccharibacteria, or TM7, have been associated with the disease periodontitis – an advanced form of gingivitis that if left untreated leads to gum loss and tooth decay. Among the TM7 bacteria, a subgroup called TM7a has been identified not only in the human oral cavity, but also on the human skin and a range of environmental sites including soil, activated wastewater (sludge), termite and rumen gut. We aim to better understand the prevalence and diversity of TM7a in the human oral cavity. Human subgingival plaque samples were taken from six healthy adults consisting of healthy and mild gingivitis sites. These samples were analyzed for the presence of total TM7 as well as TM7a using Illumina next generation sequencing based on 16S ribosomal DNA (rDNA) gene sequence. A total of 134,888 TM7 sequences were obtained, of which 13,149 were TM7a accounting for 10% of all TM7 sequences. This is the largest number of TM7 rDNA sequences reported from a single study and the only purely oral TM7 project done through the illumina platform. New phylotypes were discovered based on 97% similarity, association of TM7a to human disease was not determined.