Depleting luminal cysteine with engineered bacteroides vulgatus alleviates experimental colitis by suppressing Th17 differentiation through an ATF6-dependent mechanism

BACKGROUND: Ulcerative colitis (UC) is a chronic inflammatory bowel disease driven by dysregulated immune responses, particularly the aberrant activation of T helper 17 (Th17) cells. While microbiome-based therapies show promise, wild-type probiotics often lack specific mechanisms to target the metabolic and immunological drivers of inflammation. METHODS: In this study, we engineered a cysteine-auxotrophic strain of Bacteroides vulgatus (BV1608) by chromosomally integrating the E. coli cyuP gene to enhance cysteine uptake. We evaluated its colonization capability, safety, and therapeutic efficacy in dextran sulfate sodium (DSS)-induced acute and chronic colitis murine models. RESULTS: BV1608 exhibited superior colonization and cysteine assimilation compared to the wild-type strain. Oral administration of BV1608 significantly alleviated colitis symptoms, reduced pro-inflammatory cytokines, and restored intestinal barrier integrity. Mechanistically, BV1608 created a localized cysteine-restricted microenvironment in the gut and suppressed pathogenic Th17 differentiation. Under cystine-restricted conditions, ATF6 was activated in CD4⁺ T cells, and its inhibition partially restored IL-17A⁺ CD4⁺ T cell differentiation, indicating a functional role for ATF6. Meanwhile, cystine restriction was associated with increased BATF2 expression and enhanced ATF6 binding at the BATF2 promoter, suggesting BATF2 as a potential downstream node. CONCLUSION: Our findings demonstrate that metabolically engineered B. vulgatus BV1608 ameliorates colitis by coupling microbial cysteine sequestration with host immune modulation via the ATF6-dependent suppression of Th17 differentiation, while implicating BATF2-associated transcriptional regulation as a potential downstream mechanism. This study provides a novel synbiotic strategy for treating UC by targeting the immunometabolic interface.