Figure 1. Global distributions and abundances of human gut microorganisms at the phylum and genus levels.

Of the gut microbial taxa represented among healthy adult human populations, the Gram-positive Firmicutes and the Gram-negative Bacteroidetes appear to be universal. While different microbiota can appear similar at the phylum level (for example, Sweden versus Russia), they often differ significantly at lower taxonomic levels. In this figure, each pie chart represents an average per cohort, with outer pies depicting phylum-level taxa and Archaea, and inner pies depicting genus-level taxa within Bacteroidetes. Inter-personal variation within each country is also significant. Data adapted from ref. ¹⁴⁷.