Transcriptomics and Metabolomics Reveal the Antagonistic Mechanism of Bacillus velezensis 20507 Fermentation Broth...

Fusarium head blight (FHB), caused by Fusarium graminearum, is a devastating wheat disease leading to significant yield loss and mycotoxin contamination. This study elucidated the biocontrol mechanism of Bacillus velezensis 20507 fermentation broth against FHB during wheat infection. The broth exhibited strong, time-dependent antifungal activity in vitro, with optimal growth suppression (inhibition rates up to 75%) achieved using broth fermented for 3-7 days. In planta experiments confirmed its efficacy in alleviating disease symptoms. Employing a dual RNA-seq strategy, we analyzed the tripartite interaction between the biocontrol agent, pathogen, and wheat host. Transcriptomic analysis revealed that the broth directly suppressed the pathogen, causing 1510 differentially expressed genes (DEGs, predominantly down-regulated) and disrupting pathways related to carbohydrate metabolism and cell wall integrity. In wheat, the fermentation broth of B. velezensis 20507 counteracted F. graminearum infection by reprogramming the host transcriptome. KEGG analysis during co-inoculation showed that the broth up-regulated defense-related pathways involved in energy, hormone signaling, and cellular maintenance, while down-regulating primary metabolic pathways, indicating a resource reallocation strategy. Furthermore, transcriptomic analysis revealed that the broth alone primed the wheat defense system, and this primed state significantly enhanced the defense response upon pathogen challenge. Untargeted metabolomics identified key antimicrobial compounds, including lipopeptides and the macrolide Macrolactin A. Bioassay-guided fractionation isolated two active fractions (Fr A and Fr B) with potent antifungal activity. This integrated multi-omics study demonstrates that B. velezensis 20507 combats FHB through a coordinated dual mechanism: direct inhibition of the fungus via specific metabolites like Macrolactin A, and simultaneous reprogramming of the host defense and metabolic landscape. These findings provide a scientific foundation for developing this strain as an effective biocontrol agent.