animal host 3,471 host-associated 3,471 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 93 infant 61 ancient microbiome 58 mouth 55 ancient dental calculus 55 adolescent 51 sludge 51 lentic 38 anaerobic 37 wetland 35 wastewater 35 paludal 35 hunter-gatherer 29 soil 28 fermented food 23 food 23 traditional agriculturalist 20 fresh water 19 grassland 16 sewage 16 low salinity 14 medium temperature 14 agriculture 13 subsurface 12 groundwater 11 low temperature 10 permafrost 10 built environment 9 benthic 7 mine 7 contaminated 6 cropland 6 lotic 6 spring 6 marine 4 very high temperature 4 sea floor 4 hydrothermal vent 4 lacustrine 3 sediment 3 tundra 3 hot spring 2 lake bed 2 high temperature 2 very low temperature 2 full term birth 2 alkaline 1