Secondary Metabolite Profiling of Bacillus subtilis Strains and Their Antifungal Activity Against Alternaria and Fusarium spp.

Abstract

Secondary metabolite profiling of Bacillus subtilis strains was carried out to evaluate their antifungal potential against Alternaria and Fusarium spp. associated with major crop diseases. Indigenous B. subtilis isolates were obtained from rhizosphere soils and screened for antagonistic activity using dual culture and culture filtrate assays. Secondary metabolites were extracted from cell-free supernatants and analyzed using chromatographic and spectrometric approaches to identify key bioactive compounds. Results revealed substantial variation among strains in metabolite production profiles, including lipopeptides, polyketides, and other antifungal compounds. Selected strains exhibited strong inhibition of mycelial growth in both target pathogens, with pronounced effects on spore germination and hyphal morphology. Microscopic observations indicated hyphal distortion, cytoplasmic leakage, and growth suppression in treated fungal cultures, suggesting membrane disruption and enzymatic interference as primary modes of action. Comparative analysis showed that strains with higher concentrations of surfactin, iturin, and fengycin-like compounds demonstrated superior antifungal efficacy. The study also highlighted synergistic interactions among multiple metabolites contributing to enhanced biocontrol activity. These findings emphasize the role of B. subtilis secondary metabolites as potent antifungal agents and support their application in sustainable plant disease management. The results provide a foundation for developing microbial-based biofungicides targeting Alternaria and Fusarium-induced crop diseases.