Periodontal disease is one of the most common infectious diseases among humans, yet there is no one organism so far found responsible for this condition.  It is suspected that this and other oral diseases may be the result of interactions at the community level, rather than infection by individual species of bacteria.  We have begun to use the tools of biogeography to explore the spatial distribution of bacterial communities in the healthy human mouth, both to understand the contrasts between oral health and disease, and inform the goals of clinical treatment.  Previous studies have typically pooled samples from diverse sites within a mouth or between people to describe the oral microbiota.  As the human mouth presents a diversity of habitats at the bacterial level, we hypothesized that the community structure of the bacteria may be distributed according to the physical structure of the mouth. We sampled  the subgingival dental plaque of 23 teeth in each of three periodontaly healthy subjects.  Bacterial community DNA was extracted and sequenced at the 16S rDNA gene to identify the bacteria at each site. 
Results/Conclusions

Samples from within a single mouth are distinct from one another when sequences are analyzed by Unifrac, though the distinctions do not appear to be explained by a simple physical pattern (left vs. right, top vs. bottom, molar vs. incisor).  Sequences were identified to the genus level using RDP Classifier.  Each mouth was dominated by a different bacterial genus, and each tooth within a mouth had a different distribution of the genera found in that mouth.  Both richness and evenness of genera were variable around all 23 sites in each mouth, and also did not display a pattern by anatomical location.  Use of checkerboard scores to analyze the distribution of genera in each mouth reveals co-occurrence patterns indicative of segregation.  This raises the question of whether competition is the force driving the high levels of diversity seen even within one mouth.   We conclude that multiple bacterial communities are associated with health, communities are highly variable even within a single human mouth, and that competition may be an important factor in structuring oral bacterial communities.