Biosynthesis of Melanin with Engineered Probiotics for Oral Treatment of Ulcerative Colitis

Ulcerative colitis (UC) is a chronic intestinal inflammation characterized by immune overactivity and gut microbiota imbalance, leading to oxidative stress and inflammation. New therapeutics are required because existing ones are frequently unsuccessful and have long-term adverse effects. The research aims to manage oxidative stress and restore gut microbiota balance. The benefits of probiotics for UC can be compromised by gastrointestinal conditions that interfere with their adhesion and activity. Coating methods enhance bacterial survival in the gastrointestinal environment but face challenges like instability at low pH, short-lived effects, complexity, layer interactions, and biosafety issues. Melanin-like nanozymes are stable in the gastrointestinal environment and effectively scavenge reactive oxygen species, specifically targeting colitis lesions. We developed biosynthetic melanin-producing engineered bacteria (EcN-Mel) derived from genetically modified Nissle 1917 Escherichia coli expressing tyrosinase genes. This study evaluated the feasibility and effectiveness of administering EcN-Mel orally in UC mouse models. Results showed that EcN-Mel produced and secreted melanin, exhibiting targeted intestinal adhesion, a free radical scavenging ability, and gastrointestinal stability. In vivo imaging revealed increased colonization efficiency and retention time of EcN-Mel in inflamed intestinal segments. EcN-Mel enhances beneficial bacteria of the Lactobacillus genus while decreasing harmful members of the Proteobacteria genus, promoting gut microbiota homeostasis, and alleviating colitis. EcN-Mel alleviated intestinal mucosal damage through combined actions, including gut microbiota modulation, oxidative stress reversal, cytokine regulation, and barrier restoration. Our findings confirm the safety, feasibility, and effectiveness of EcN-Mel for UC treatment.