Oral Distribution of Saccharibacteria (TM7) Taxa and Co-associations with Other Bacteria

Objectives: Saccharibacteria (formerly known as Division TM7) belongs to the Candidate Phyla Radiation group of bacteria. Members of this group have ultra-small cells and exhibit obligate epiobiontic relationships with other bacteria. A provisional taxonomy based on the phylogenetic analysis of 16S rRNA genes has placed oral Saccharibacteria in 8 genera in the Human Oral Microbiome Database. One strain of Saccharibacteria, belonging to taxon HMT-952, a member of Saccharibacteria genus 1, has been isolated in co-culture with an Actinomyces odontolyticusstrain. The aim of this study was to determine the abundance and distribution of Saccharibacteria oral taxa in saliva and plaque and to investigate associations between the presence of Saccharibacteria and other oral taxa in order to identify additional putative co-culture partners.
Methods: The prevalence and relative abundance of Saccharibacteria taxa were determined in three different 16S rRNA sequence datasets: 1) saliva from children (n=207); 2) plaque (n=163) and saliva (n=177) from the same subjects; 3) plaque (n=48) from carious and non-carious sites of 16 individuals. Spearman correlation was calculated between the relative abundances of Saccharibacteria and other species.
Results:
Saccharibacteria were present in 558/595 of samples overall; 15 HMTs from all 8 genera were detected. G-1 had the highest mean abundance (0.54%) and prevalence (71% of samples). G-5 was the next most abundant (0.35%) and was detected primarily in plaque (0.8% abundance, 69.2 % prevalence) compared to saliva (0.06 % and 25%). In plaque, G-5 was significantly correlated with Treponemasp. HMT-237, Dialister pneumosintes, Dialister invisusand 21 other species (p<0.001), mainly obligate anaerobes.
Conclusions: Efforts should be focused towards the culture of Saccharibacteria G-5, given its numerical importance in plaque. This study has revealed some potential co-culture host organisms.