ABSTRACT Worldwide, one in five children under five years of age manifests undernutrition as impaired linear growth, or stunting. Stunting, defined as having a length-for-age z-score (LAZ) < -2, is associated with poor developmental outcomes, including impaired neurodevelopment and immune responses. Furthermore, stunting and its long- term sequelae persist across generations, contributing to an intergenerational cycle of undernutrition. Existing nutritional interventions fail to substantially improve stunting, highlighting the need to (i) better understand other factors contributing to stunting and (ii) focus clinical efforts towards treating maternal undernutrition in order to break the cycle of intergenerational undernutrition. In recent years, a subclinical disorder called environmental enteric dysfunction (EED) has been suggested to contribute to 45% of childhood stunting globally. EED is an inflammatory enteropathy localized to the small intestine; it is characterized histologically by loss of villi and absorptive surface area, epithelial barrier dysfunction, and an immunoinflammatory infiltrate in the lamina propria. While the pathogenesis of EED is poorly understood, researchers have postulated a role for enteric microorganisms. However, the small intestinal microbiota remains largely understudied, in part due to challenges in gaining access to samples. Moreover, few experimental models of EED exist, none of which account for the intergenerational nature of undernutrition. I hypothesize that perturbations in the small intestinal microbiota play a causal role in the pathogenesis of EED and consequently undernutrition that persists across generations. To test this hypothesis, the first aim of this proposal will use gnotobiotic mice to characterize the transmissibility of enteropathy and growth faltering by the small intestinal microbiota of Bangladeshi children and women with evidence of EED based on histopathology of their duodenal biopsies. Collections of sequenced bacterial strains, cultured from duodenal aspirates obtained from these stunted children and malnourished women (BMI<18.5 kg/m2) will be introduced into young germ-free mice. I will characterize host pathology by performing immune cell profiling, protein immunoassays, and transcriptional profiling (whole tissue and single cell). Microbial community structure will be quantified by shotgun sequencing of community DNA, and expressed community functions by microbial RNA- Seq. In parallel, I will establish a novel model of intergenerational undernutrition by introducing these microbia l communities into germ-free dams and assessing the pathology in dams and their pups. The second aim will test prevention and/or treatment of enteropathy in the gnotobiotic mouse models through introduction of duodenal bacterial communities derived from healthy Bangladeshi women (with normal BMI). Prevention or amelioration of enteropathy by duodenal bacterial communities from healthy women will allow f...