This study evaluated the potential of individual and co-inoculation with Bacillus velezensis (Bv) and Pseudomonas helmanticensis (Ph) as microbial decomposers for corn straw. The co-inoculation (BP) treatment demonstrated the highest total mass loss for cellulose, hemicellulose, and total straw, significantly outperforming the single-strain treatments (Bv and Ph) and the non-inoculated control (CK). All inoculated treatments consistently enhanced degradation over time and lowered pH compared to CK. High-throughput sequencing revealed that inoculation dramatically reshaped the soil microbial community. All treatments reduced microbial ASVs and bacterial alpha diversity (ACE, Chao1, Shannon), with the most pronounced effect observed for Bv. Beta diversity analysis showed distinct, treatment-specific clustering. Critically, FUNGuild analysis indicated a significant functional shift, with all inoculants increasing saprotroph abundance and decreasing pathotrophs. The BP consortium exhibited a synergistic effect, driving saprotroph dominance to >96%. These results demonstrate that the synergistic co-inoculation enhances straw decomposition by restructuring the microbial community towards functional dominance of saprotrophs.

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.

Soybean, as a globally important economic crop, is severely threatened by Sclerotinia sclerotiorum, the causative agent of Sclerotinia stem rot (SSR), a major disease in soybean production worldwide, leading to significant yield losses and quality deterioration. Traditional chemical control methods face challenges such as environmental pollution, pesticide resistance, and limited efficacy. Bacillus velezensis YJ0-1, identified through plate confrontation assays, demonstrated significant inhibitory effects on S. sclerotiorum via acid-precipitated crude extracts from its fermentation broth. A key antimicrobial substance, fengycin (C₇₂H₁₁₀N₁₂O₂₀, molecular weight 1463.8 Da), was isolated and characterized through acid precipitation, protein purification system separation, and mass spectrometry (MS). Further optimization of the PDB medium using single-factor experiments and Box–Behnken design yielded an optimal formulation: peptone 66.62 g/L, sucrose 32.68 g/L, and pH 6.5. Validation experiments showed an actual yield of 2.03 g/L, with a relative error of only 0.49% compared to the predicted yield of 2.04 g/L, significantly enhancing the synthesis efficiency of fengycin. This study provides novel microbial resources and a theoretical basis for the biological control of SSR in soybeans, while also laying a technical foundation for the industrial production of fengycin, contributing to the advancement of sustainable agriculture.