Xinyu Sun ¹ Long Yun ² Keming Xie ³ Renhui Liu ⁴ Xinyue Ren ¹ Bokun Zeng ¹ Xudong Cao ⁵ Zhi Li ⁶ GuiHao Zhou ⁷ Bang Liu ¹ Peng Luo ^8* Li-Hong Yuan ^1*

• ¹ School of Life Sciences and Biopharmaceutics, Guangdong Pharmaceutical University, Guangzhou, China
• ² Huzhou Key Laboratory of Translational Medicine, First Affiliated Hospital of Huzhou University, Huzhou, China
• ³ Medical College of Jiaying University, Meizhou, Guangdong Province, China
• ⁴ School of Sport Medicine,Wuhan Sport University, Wuhan, China
• ⁵ Department of Chemical and Biological Engineering, University of Ottawa,, Ottawa, Canada
• ⁶ Key Laboratory of Aquacultural Biotechnology Ministry of Education, School of Marine Sciences, Ningbo University, Ningbo, China
• ⁷ University College London, London, England, United Kingdom
• ⁸ KeyLaboratory of Applied Marine Biology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, guangzhou, China

Purpose: Gut microbiota dysbiosis significantly impacts ulcerative colitis (UC) progression and exacerbation. Probiotics show promise in UC management. This study evaluated the effects of different doses of Bacillus pumilus LV149, an aquatic-derived probiotic, on gut injury repair in male C57BL/6 mice with dextran sulfate sodium (DSS)-induced ulcerative colitis (UC) and investigated the underlying mechanisms.Methods: UC was induced by allowing mice free access to a 3% DSS solution for seven days, with concurrent daily oral gavage of either a low (LV149-L, 1×10 8 CFU/day/mouse) or high (LV149-H, 1×10 9 CFU/day/mouse) dose of LV149. The effects were assessed through physiological parameters, intestinal barrier integrity, inflammation, gut microbiota composition, and transcriptomic changes.Results: LV149 significantly improved pathological symptoms, including weight loss and disease activity index (DAI), and reduced colon shortening in a dose-dependent manner and inflammatory damage. The intervention also restored gut barrier function by upregulating mucins, goblet cell counts, and tight junction proteins (ZO-1, Occludin, Claudin-1) in colonic tissue, along with reducing serum lipopolysaccharide (LPS) levels. Notably, only the LV149-H significantly decreased the expression of proinflammatory cytokines TNF-α, IL-1β, and IL-6, while both doses increased the expression of the anti-inflammatory cytokine IL-10 in a dose-dependent in colonic tissue. LV149 further modulated the gut microbiota, increasing beneficial bacteria and reducing pathogenic populations. Transcriptomic analysis indicated that LV149-L may exert gut repair effects via the IL-17 pathway, whereas LV149-H appears to act through the JAK-STAT signaling pathway.This study demonstrated that LV149, particularly at a higher dose, effectively mitigated DSS-induced colonic injury by modulating gut microbiota, enhancing gut barrier integrity, and reducing inflammation. The dose-dependent effects underscored LV149-H's potential as a therapeutic agent for UC due to its stronger antiinflammatory properties and gut-protective effects.