animal host 5,325 host-associated 5,325 digestive tract 5,301 mammalian host 5,095 intestine 4,612 human host 3,551 industrialized 2,635 adult 1,565 mouth 1,023 saliva 728 child 536 non-industrialized 406 infant 371 urban 364 rural 358 elderly 264 preterm birth 208 rumen 173 anthropogenic 163 aquatic 162 adolescent 162 terrestrial 111 wastewater 100 ancient microbiome 75 sewage 68 ancient dental calculus 68 airways 57 sludge 51 built environment 41 anaerobic 27 agriculture 25 hunter-gatherer 24 lentic 23 traditional agriculturalist 22 fresh water 22 full term birth 20 benthic 19 urogenital tract 18 sediment 17 marine 17 low salinity 15 high salinity 15 soil 13 low temperature 13 medium temperature 12 subsurface 12 contaminated 11 groundwater 9 alkaline 9 hospital 7 cropland 7 lacustrine 7 very low temperature 6 paludal 6 wetland 6 mine 5 insect host 4 littoral 3 very high salinity 3 waste 3 skin 2 stream 2 brackish water 2 grassland 2 medium salinity 2 lotic 2 high temperature 2 coral reef 1 sea floor 1 saline water 1 spring 1 hydrothermal vent 1 fluvial 1 very high temperature 1 pelagic 1