Fig. 5.

Microbial diversity of the human intestine. OTU richness was estimated for a data set of sequences obtained in this study and those of Eckburg et al. (44) and Ley et al. (32). Sequences were clustered into OTUs and averaged collector's curves simulated by 1,000 random replicate samplings of the OTUs at sample sizes ranging from 1,000 to 45,000 sequences (total sequences, 45,172). The graph shows double reciprocal plots of mean S_obs⁻¹ vs. sequences⁻¹ for 99%, 97%, and 95% OTUs. The Y intercepts of the graphs were extrapolated by linear regression of S_obs⁻¹ and sequences⁻¹, from which expected OTU richness (i.e., S_max) was inferred. The dashed lines extending from each graph approximate the extrapolations.