Abstract Background Chronic exposure to low‑dose lipopolysaccharide (LPS) in poultry farming environments induces persistent respiratory inflammation, resulting in lung injury and impaired growth performance in broilers. Bacillus velezensis (BV) is a probiotic with known antibacterial and immunomodulatory activities, yet its role in respiratory health remains poorly understood. This study aimed to assess the potential benefits of BV in alleviating chronic pneumonia triggered by LPS in broilers and to clarify its mechanistic pathways. Results A chronic LPS intratracheal instillation model was established, comprising control, LPS, and BV + LPS groups. BV supplementation significantly ameliorated LPS‑induced growth impairment ( P < 0.05), inhibited the synthesis of key inflammatory mediators, and mitigated oxidative stress in serum and bronchoalveolar lavage fluid ( P < 0.05). Integrated multi‑omics analyses revealed that BV remodeled the pulmonary microbiota, enriching isoflavone‑metabolizing taxa including Blautia and unclassified Lachnospiraceae ( P < 0.05), which was associated with elevated pulmonary concentrations of daidzein, genistein, and glycitein ( P < 0.05). Transcriptomic together with molecular analyses revealed that BV enhanced the activation of PPAR‑γ while attenuating NF‑κB pathway activity, thereby reducing the expression of genes associated with inflammation ( P < 0.05). In vitro, experiments showed that daidzein and genistein inhibited cellular inflammatory responses through PPAR-γ signaling. BV culture supernatant directly suppressed NF‑κB/NLRP3 inflammasome activation in chicken HD11 macrophages, reduced intracellular reactive oxygen species (ROS) generation, and shifted macrophage polarization toward an anti‑inflammatory phenotype ( P < 0.05). Conclusion These findings demonstrate that BV alleviates LPS-induced chronic pneumonia through two complementary pathways, as it remodels the pulmonary microbiota to enhance isoflavone metabolism and thereby suppress inflammation, while its own metabolites also directly inhibit inflammatory signaling. This study provides new insight into probiotic-based interventions for respiratory health in livestock.
Zhang et al. (Wed,) studied this question.