Genomic and Functional Characterization of Bacillus subtilis Strain 55-7 as a Dual-Function Bioinoculant for Fungal Biocontrol and Enhancing Sweet Corn Seedling Growth Under Reduced Fertilizer Input.

Fungal pathogens and unsustainable fertilizer use pose a threat to global food security, driving demand for eco-friendly alternatives to conventional disease management and crop fertilization. This study characterizes Bacillus subtilis strain 55-7, isolated from a saline hot spring in Krabi, Thailand, as a dual-function bioinoculant for sustainable plant cultivation. Laboratory assays demonstrated potent antifungal activity against Curvularia lunata (91.9% by volatile organic compounds and 49.1% by confrontation assay) and multiple plant growth-promoting traits, including nitrogen fixation, phosphate solubilization, siderophore production, and IAA synthesis. In greenhouse trials, combining strain 55-7 with 50% reduced N-P-K fertilizer enhanced sweet corn shoot biomass by 2.9-fold and root length by 70.8% compared to the control, matching full-fertilizer performance. Whole-genome sequencing revealed 4,324 genes within a 4.06 Mb genome, and ten biosynthetic gene clusters with low similarity (16-73%) to known antimicrobial pathways, suggesting novel or uncharacterized variants of the secondary metabolites. These findings position B. subtilis strain 55-7 as a promising bioinoculant for integrated crop management, reducing chemical inputs while maintaining productivity.