Divalent Metal Ion Dictates Probiotic Intestinal Retention and Mucoadhesion

Abstract Probiotic colonization in the gastrointestinal tract is a prerequisite for their therapeutic efficacy. However, under pathological conditions such as inflammatory bowel disease, the intestinal microenvironment imposes colonization resistance through multiple converging factors, severely limiting probiotic retention. Dietary metal ions and polyphenols have each been reported to influence probiotic behavior, yet whether their coordinated action through metal-phenolic network coatings produces differential effects on colonization enhancement depending on the metal ion species remains unclear. In this study, tannic acid was selected as the representative polyphenolic ligand, and three divalent metal ions, Fe2+, Ca2+, and Mg2+, were systematically compared for their capacity to enhance intestinal colonization of Lactobacillus paracasei after assembly into metal-phenolic network coatings. The results demonstrated that LP@Ca2+/TA significantly outperformed LP@Fe2+/TA and LP@Mg2+/TA in terms of gastrointestinal fluid tolerance, intestinal retention time, and mucosal adhesion. Mechanistically, LP@Ca2+/TA not only enhanced bacterial adhesion to the mucus layer but also upregulated MUC2 secretion, preserved epithelial tight junction integrity, and enriched beneficial bacterial families including Lactobacillaceae and Akkermansiaceae, while simultaneously improving bacterial co-aggregation capacity, collectively contributing to enhanced probiotic intestinal colonization. This study provides a reference for the screening and rational design of metal ions in metal-phenolic network-based probiotic coatings, among which Ca2+ demonstrated the most prominent performance among the three divalent dietary metal ions tested.