Even in the absence of active inflammation, persistent symptoms are reported in up to 46% of patients with Crohn's disease (CD). Persistent symptoms in quiescent CD (labeled qCD+S in this grant) result in significant deterioration in quality of life, increase risk for future opioid use, and are among the top drivers of healthcare costs in CD. Increased intestinal permeability and visceral hypersensitivity are key pathogenic features in patients with qCD+S. Although initially believed to be related to sub-clinical inflammation, recent studies have shown no difference in the rate of persistent symptoms in CD patients with and without deep histologic remission. Importantly, evidence-based treatments do not exist due to lack of understanding of the mechanisms leading to qCD+S. Recently, altered gut microbiota have been implicated but the mechanisms by which altered microbial communities may mediate qCD+S remain unknown. A promising development shown by our preliminary data is enrichment of sulfidogenic bacteria and sulfur metabolic pathways in patients with qCD+S. Dietary sulfur is metabolized by the intestinal microbiota to produce hydrogen sulfide (H2S), which is rapidly detoxified by host mitochondrial enzymes to protect the host against toxic effects of H2S. However, at higher concentrations, microbial-derived H2S may overwhelm host mitochondrial H2S detoxifying capacity. As a result, increased H2S levels may result in mitochondrial dysfunction, disrupt intestinal barrier function, and exert pro-nociceptive effects. Diet, particularly consumption of animal protein, is the major determinant of H2S production in the gut. However, the relationship between diet, sulfidogenic microbes, epithelial barrier function, and visceral sensation in qCD+S is unknown. Thus, there is a critical need to examine the interplay between diet, sulfidogenic microbes, host responses, and persistent symptoms in quiescent CD. The long-term goal of this project is to accelerate development of microbial-based treatments for qCD+S. The central hypothesis is that enrichment of sulfidogenic microbes result in dysregulated host responses, including intestinal barrier dysfunction and visceral hypersensitivity, which may be amenable to dietary intervention. In Aim 1, we will determine how sulfidogenic microbes influence host gene expression in qCD+S by integrating existing multi- omic datasets from a multi-center cohort, including metagenomic and untargeted metabolomics data from stool samples as well as host gene expression from intestinal biopsies. In Aim 2, we will perform a pilot study to determine the feasibility and tolerability of a low sulfur diet in qCD+S. We will also test whether a low sulfur diet may improve intestinal permeability, visceral sensation, and persistent symptoms and whether these changes are mediated by perturbations in sulfidogenic microbes. Completion of these aims will provide fundamental insights into diet-host-sulfidogenic microbial interactions in q...