Iron homeostasis in sustaining commensal resilience in the inflamed gut - Abstract The homeostatic gut microbiota provides essential functions to multiple aspects of human health, including modulating the interactions between host and enteric pathogens. Perturbations, such as intestinal inflammation, can shift the beneficial microbiota to an imbalanced state frequently referred to as dysbiosis, which instead exacerbates inflammatory disease outcomes in susceptible individuals. As such, microbial resilience is crucial to maintaining the structural and functional stability of the gut microbiome in the face of perturbations. Despite the central role in host health, mechanisms underlying microbiota resilience remain largely unexplored. During intestinal inflammation, the host immune system impedes invading pathogens through the sequestration of iron, among other micronutrients, in a process termed nutritional immunity. While decades of research have described how pathogens utilize small iron-chelating molecules termed siderophores to survive and thrive in the iron-starved inflamed gut, commensal survival strategies during nutritional immunity remain largely unknown. Our preliminary studies suggested that the prominent gut commensal Bacteroides thetaiotaomicron (B. theta) can capture iron from siderophores produced by enteric pathogens. Additionally, B. theta can prioritize its iron expenditure through the activation of a small RNA-mediated iron-sparing response, thereby conserving the limited iron for essential cellular processes. I hypothesize that B. theta couples xenosiderophore piracy and iron-sparing response through the action of small RNA to maintain resilience in the iron-limited inflamed gut. I will test this hypothesis using genetic, biochemical, and computational approaches in tandem with in vitro growth assays and murine models of infectious colitis. Experiments proposed in Aim 1 will determine the contribution of xenosiderophore piracy to B. theta fitness, using in vitro growth kinetics and mouse models of intestinal inflammation. Experiments in Aim 2 will define the mechanism, regulatory targets, and fitness contribution of iron-responsive B. theta sRNA during iron-limitation in vitro and in vivo. This proposed work is innovative because it presents a heretofore unexplored microbial factor in microbiome structure during intestinal inflammation. This proposed work is impactful because establishing a model for iron regulation in B. theta will provide insights into how interphylum iron metabolism and intracellular iron homeostasis may broadly contribute to gut microbiota resilience in the inflamed gut.
