Engineering Microbial Tryptophan Metabolic Pathways for Controllable Activation of AhR

The gut microbiota plays a critical role in host physiology. Individual microbes can metabolize components from the diet or produced by the host with their unique set of genetic capabilities. A key mediator in the relationship between host and microbes is tryptophan, originating from exogenous dietary sources. Intestinal microorganisms can metabolize tryptophan into a wide range of downstream metabolites including tryptamine, indole-3-aldehyde, kynurenine, and indole-3-acetic acid. These indole derivatives play a crucial role in regulating host physiology through their interactions with the aryl hydrocarbon receptor (AhR). AhR is crucial for maintaining a functional epithelial barrier and resistance to gut inflammation, in part due to activation of pathways including IL-22 and the production of antimicrobial peptides. Current studies find design challenges with physiological relevance when administering AhR ligands in drinking water or whole bacterium with the ability to produce a wider range of AhR ligands. Our approach will address these issues by engineering single strains containing a biosynthetic pathway for a single AhR ligand to investigate the effects of individual ligands in the most physiological relevant spaces. Altering tryptophan metabolite production within tractable gut commensal, Bacteroides fragilis, will allow specific and controllable activation of AhR within the gut microbiome to positively affect host physiology.