a Schematic overview of engineered curli production. Genetically engineered E. coli Nissle 1917 (EcN) with csg (curli) operon deletion (PBP8 strain) containing plasmids encoding a synthetic curli operon capable of producing chimeric CsgA proteins (yellow chevrons with appended bright green domains), which are secreted and self-assembled extracellularly into therapeutic curli hybrid fibers. b CsgA (yellow), the main proteinaceous component of the E. coli biofilm matrix, was genetically fused to a therapeutic domain—in this case, TFF3 (PDB ID: 19ET, bright green), which is a cytokine secreted by mucus-producing cells. The flexible linker (black) includes a 6xHis tag for detection purposes. c Engineered bacteria are produced in bulk before delivery to the subject via oral or rectal routes. A site of colonic inflammation is highlighted in red. d Interaction of PATCH and the colonic mucosa. Inflammatory lesions in IBD result in loss of colonic crypt structure, damage to epithelial tissue, and compromised barrier integrity (left panel, (−) PATCH). The resulting invasion of luminal contents and recruitment of immune cells to the site exacerbates the local inflammation. The application of PATCH (right panel, (+) PATCH) reinforces barrier function, promotes epithelial restitution, and dampens inflammatory signaling to ameliorate IBD activity.^[1]