host-associated 4,055 animal host 4,053 digestive tract 4,048 intestine 4,022 mammalian host 3,777 human host 3,430 industrialized 2,897 adult 1,532 urban 449 elderly 195 rural 159 non-industrialized 152 aquatic 126 child 88 adolescent 87 terrestrial 61 fresh water 60 anthropogenic 52 infant 50 low salinity 45 lentic 35 subsurface 29 benthic 28 lacustrine 26 groundwater 25 wastewater 25 marine 21 contaminated 21 mouth 21 sediment 20 sewage 20 sludge 15 high salinity 13 rumen 11 ancient microbiome 10 ancient dental calculus 9 lotic 9 mine 8 anaerobic 8 spring 8 alkaline 7 sea floor 6 full term birth 6 hydrothermal vent 6 soil 6 traditional agriculturalist 6 very high temperature 6 saliva 5 low temperature 5 insect host 5 medium temperature 4 coral reef 4 built environment 3 very high salinity 3 wetland 3 hunter-gatherer 3 waste 3 paludal 3 hot spring 2 very low temperature 2 stream 2 hospital 2 plant host 2 fluvial 1 phyllosphere 1 lake bed 1 high temperature 1 littoral 1 agriculture 1 brackish water 1 medium salinity 1