host-associated 39,877 animal host 39,868 digestive tract 39,616 mammalian host 38,408 intestine 38,285 human host 33,551 industrialized 26,830 adult 15,469 urban 4,823 infant 4,558 child 3,410 elderly 2,676 rural 2,272 non-industrialized 2,108 mouth 1,594 saliva 1,111 adolescent 1,030 preterm birth 834 full term birth 710 anthropogenic 626 rumen 589 traditional agriculturalist 508 terrestrial 478 aquatic 471 wastewater 254 built environment 238 hunter-gatherer 186 sewage 172 sludge 151 ancient microbiome 112 airways 108 skin 101 urogenital tract 90 lentic 82 soil 81 agriculture 76 ancient dental calculus 73 fresh water 68 anaerobic 52 low salinity 51 marine 48 insect host 44 subsurface 42 wetland 39 paludal 37 benthic 37 medium temperature 36 sediment 34 hospital 32 food 30 groundwater 30 contaminated 29 fermented food 26 high salinity 25 low temperature 23 lacustrine 21 lotic 20 spring 19 alkaline 18 hot spring 18 grassland 17 very low temperature 16 tundra 16 mine 15 cropland 11 very high salinity 10 plant host 9 permafrost 8 saline water 7 ice 7 waste 6 littoral 5 forest 5 rhizosphere 4 dairy product 4 arid 3 very high temperature 3 high temperature 3 stream 3 medium salinity 2 air 2 coral reef 2 brackish water 2 mangrove 2 hydrothermal vent 1 pelagic 1 phyllosphere 1 fluvial 1 sea floor 1 briny water 1 lake bed 1 negative control 1