BEAMS ABSTRACT: Project 3 BEAMS seeks to understand how differences in environmental and personal microbiota determine differences in asthma prevalence by exploring a unique human model: populations of comparable Mexican ancestry that live 70 miles apart in Tucson, AZ, and Nogales, MX, but differ profoundly in childhood asthma rates (4-fold lower in MX) and the microbial composition of children?s stool, drinking water and house dust. Project 3 builds on our findings that 1) microbe-rich environments [e.g., traditional Amish (AM) farms] protect from asthma; 2) inhalation of AM house dust is sufficient to protect mice from allergic asthma; 3) unmanipulated stools of healthy preschool AM children, but not high-risk Hutterite children, protect associated germ-free (GF) mice from asthma through selected microbial taxa and novel innate mechanisms; 4) individual AM stool metabolites are sufficient to protect specific pathogen-free (SPF) mice from allergic lung inflammation; and 5) US and Mexican environmental samples (house dust and drinking water) differentially protect mice from allergic asthma. These data demonstrate that both environmental and gut microbiota are critical for asthma protection in natural populations, and lead us to hypothesize that exposure to distinct environmental microbiota (especially from house dust and drinking water) differentially shapes the composition and metabolic profile of gut microbiota in US and Mexican pregnant women, thereby differentially shaping gut microbiota, immune development and trajectory to asthma in their children. More specifically, we hypothesize that the microbial environments prevalent in Mexican homes, and the gut microbiota especially abundant in pregnant Mexican women and their young children, are enriched in taxa and metabolites that suppress type-2 responses and asthma. We will test our hypothesis using an innovative approach that combines environmental and personal gut microbiota within a single experimental framework: the impact of environmental exposures on gut microbiota development, immune responses and asthma will be studied in pregnant or young GF mice that first will be ?humanized? by association with stools of 40 mother/infant dyads (20 per location), then will be exposed to paired dust and drinking water from the subjects? homes, and finally will be tested in a classic allergic asthma model. Specifically, we propose to assess how vertical transmission of stool microbiota from US or Mexican pregnant women and early exposure to environmental microbiota differentially affect the development of asthma, immune responses and gut microbiome in the progeny of associated GF mice (Aim 1); how microbiota enriched in the meconium of US or Mexican neonates and early exposure to paired environmental microbiota differentially influence the development of asthma, immune responses and gut microbiome in associated young GF mice (Aim 2); which infant stool metabolites protect from asthma in vivo (Aim 3). Our work will elucidate the mechanisms that link environmental exposures to gut microbiota development, immune responses and asthma protection.