Figure 2. Bacterial abundance types.

Bacterial abundance types include symmetric, skewed and bimodal logarithmic abundance distributions (Supplementary Table 1). The skewed types include prevalent left- and right-skewed types as well as rare bacteria. The bimodal types (Fig. 1) include cases with two distinct peaks, and cases with a peak at low abundance combined with a more widely varying fat tail of high-abundance subjects. The population frequencies of the log abundance across the 1,006 western adults are shown for representative examples from each category: Anaerostipes caccae et rel. (symmetric); Serratia spp. (rare); Streptococcus bovis et rel. (right skewed); Faecalibacterium prausnitzii et rel. (left skewed); P. oralis et rel. (bimodal distribution with two distinct peaks); and uncultured Clostridiales I (fat tailed, bimodal distribution with a variable high-abundance state).