host-associated 21,136 animal host 21,136 digestive tract 21,125 intestine 21,118 mammalian host 20,676 human host 19,990 industrialized 17,007 adult 9,042 urban 3,171 infant 1,706 elderly 1,665 child 1,311 adolescent 605 rural 430 full term birth 338 non-industrialized 304 preterm birth 138 traditional agriculturalist 51 anthropogenic 50 terrestrial 37 aquatic 37 wastewater 35 built environment 33 sewage 19 ancient microbiome 13 hospital 13 skin 10 hunter-gatherer 9 sludge 7 agriculture 4 soil 4 rumen 3 marine 2 medium temperature 2 anaerobic 2 mouth 1 fermented food 1 low temperature 1 food 1 air 1 saliva 1 urogenital tract 1