animal host 3,470 host-associated 3,470 digestive tract 3,466 mammalian host 3,330 intestine 3,167 human host 2,484 industrialized 1,922 adult 765 non-industrialized 340 child 307 rural 304 rumen 293 elderly 251 urban 149 anthropogenic 130 terrestrial 118 aquatic 89 infant 61 ancient microbiome 58 mouth 55 ancient dental calculus 55 adolescent 51 sludge 51 lentic 38 anaerobic 37 wetland 35 paludal 35 wastewater 35 hunter-gatherer 29 soil 28 food 23 fermented food 23 traditional agriculturalist 20 fresh water 19 grassland 16 sewage 16 medium temperature 14 low salinity 14 agriculture 13 subsurface 12 groundwater 11 permafrost 10 low temperature 10 built environment 9 mine 7 cropland 6 contaminated 6 lacustrine 3 benthic 3 tundra 3 sediment 3 full term birth 2 lotic 2 spring 2 high temperature 2 lake bed 2 very low temperature 2 hot spring 2 alkaline 1