Bacillus velezensis GFZF-23 Alleviates Colitis through Microbiome Restoration and β-Sitosterol-Mediated Metabolic Reprogramming

BackgroundA major hurdle in probiotic development for inflammatory bowel disease (IBD) is the inability to disentangle their direct effects on the host from those mediated through the resident microbiota. Here, we establish a reverse screening platform in gnotobiotic zebrafish to overcome this limitation. ResultsWe isolated Bacillus velezensis (B. velezensis) GFZF-23 from long-surviving gnotobiotic zebrafish and demonstrated its potent protective effects against DSS-induced colitis. The strain significantly attenuated intestinal damage and inflammatory responses in both germ-free and conventional hosts. Multi-omics analysis revealed that B. velezensis GFZF-23 employs environment-specific strategies. In the presence of a microbiome, it restored community homeostasis by enriching beneficial taxa, such as Faecalibacterium. Strikingly, in germ-free conditions, GFZF-23 did not simply reverse disease-associated markers but actively reprogrammed host metabolism, with particular enrichment in the linoleic acid pathway. Functional assays confirmed that {beta}-sitosterol serves as a critical effector metabolite driving this protection. ConclusionsThis work establishes B. velezensis as a promising therapeutic candidate and provides a robust framework for deconvoluting the direct and indirect effects of potential probiotics. Our findings highlight metabolic reprogramming as a vital, underappreciated mechanism in precision microbiome therapeutics. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=112 SRC="FIGDIR/small/710680v1_ufig1.gif" ALT="Figure 1"> View larger version (60K): org.highwire.dtl.DTLVardef@10868e6org.highwire.dtl.DTLVardef@11f1532org.highwire.dtl.DTLVardef@1a88631org.highwire.dtl.DTLVardef@1020b33_HPS_FORMAT_FIGEXP M_FIG C_FIG