animal host 17,625 host-associated 17,625 digestive tract 17,618 intestine 17,616 mammalian host 17,352 human host 16,479 industrialized 13,581 adult 7,745 urban 2,413 child 1,394 elderly 1,276 rural 1,128 non-industrialized 1,009 infant 742 adolescent 583 full term birth 211 traditional agriculturalist 171 hunter-gatherer 56 anthropogenic 39 aquatic 36 wastewater 34 sewage 31 preterm birth 23 terrestrial 21 built environment 16 ancient microbiome 12 low temperature 10 hospital 10 soil 8 skin 7 marine 2 medium temperature 2 air 1 very low temperature 1 sludge 1