Quantifying shared and unique gene content across 17 microbial ecosystems
Measuring microbial diversity is traditionally based on microbe taxonomy. Here, in contrast, we aimed to quantify heterogeneity in microbial gene content across 14,183 metagenomic samples spanning 17 ecologies including -- 6 human-associated, 7 non-human-host-associated, and 4 in other non-human host environments. In total, we identified 117,629,181 non-redundant genes. The vast majority of genes (66%) occurred in only one sample (i.e. "singletons"). By contrast, we found 1,864 sequences present in every metagenome, but not necessarily every bacterial genome. Additionally, we report datasets of other ecology-associated genes (e.g. abundant in only gut ecosystems) and simultaneously demonstrated that prior microbiome gene catalogs are both incomplete and inaccurately cluster microbial genetic life (e.g. at gene-sequence identifies that are too restrictive). We provide our results and the sets of environmentally-differentiating genes described above at http://www.microbial-genes.bio. ImportanceThe amount of shared genetic elements has not been quantified between the human microbiome and other host and non-host associated microbiomes. Here we made a gene catalog of 17 different microbial ecosystems and compared them. We show that most species shared between environment and human gut microbiomes are pathogens and that prior gene catalogs described as "near-complete" are far from it. Additionally, over two-thirds of all genes only appear in a single sample and only 1,864 genes (0.001%) are found in all types of metagenomes. These results highlight the large diversity between metagenomes and reveal a new, rare class of genes, those found in every type of metagenome, but not every microbial genome.