Role of iturin from Bacillus velezensis DMW1 in suppressing growth and pathogenicity of Plectosphaerella cucumerina in tomato by reshaping the rhizosphere microbial communities.

Plant-associated microbiomes play a crucial role in suppressing plant and soil pathogens. However, the mechanisms by which pathogen invasion influences the interaction between bacteria and fungi remain unknown and warrant further investigation. In this study, Bacillus spp. was found to be more abundant in diseased rhizosphere in the presence of the soil-borne fungus Plectosphaerella cucumerina. Most of the isolated Bacillus spp. exhibited a robust ability to balance reactive oxygen species (ROS) and demonstrated broad-spectrum antagonistic activity against P. cucumerina, Phytophthora capsica, Fusarium oxysporum, and Ralstonia solanacearum. The secondary metabolite iturin was identified as the key antifungal compound produced by the representative strain Bacillus velezensis DMW1, which effectively inhibits fungal growth and disrupts cell structures. Transcriptome analysis revealed that fungi treated with iturin (28.67 µg/mL) exhibited 4995 differentially expressed genes (DEGs), including 2611 upregulated genes and 2384 downregulated genes, compared to the control group. Furthermore, the application of DMW1 and return-deficient mutant (Δitu) significantly altered microbial diversity and enriched beneficial microorganisms in the rhizosphere soil. The overall findings highlight the potential of DMW1 as a promising biological agent for controlling soil-borne diseases. Its strong antimicrobial properties, ability to colonize host plants effectively, and capacity to reshape the soil microbiota make it a valuable resource for enhancing microbial ecosystems and providing long-term benefits to plants.