Figure 1. Compositional differences in the microbiome by anatomic site.

High-throughput sequencing has revealed substantial intra-individual microbiome variation at different anatomical sites, and inter-individually for the same anatomical sites ^{4,5,25,52,89,93}. However, higher level (e.g. phylum) taxonomic features display temporal (longitudinal) stability in individuals at specific anatomical sites. Such site-specific differences as well as observed conservation between human hosts provide an important framework to determine the biological and pathological significance of a particular microbiome composition. The figure indicates percentages of sequences at the taxonomic phylum level from selected references. Certain features, such as the presence or absence of Helicobacter pylori, can lead to permanent and marked perturbations in community composition⁹³.