The Extracellular Lipopeptides and Volatile Organic Compounds of Bacillus subtilis DHA41 Display Broad-Spectrum Antifungal Activity against Soil-Borne Phytopathogenic Fungi.

Fusarium oxysporum f. sp. niveum ( Fon ) is a devastating soil-borne fungus causing Fusarium wilt in watermelon. The present study investigated the biochemical mechanism underlying the antifungal activity exhibited by the antagonistic bacterial strain DHA41, particularly against Fon . Molecular characterization based on the 16S rRNA gene confirmed that DHA41 is a strain of Bacillus subtilis , capable of synthesizing antifungal lipopeptides, such as iturins and fengycins, which was further confirmed by detecting corresponding lipopeptide biosynthesis genes, namely ItuB , ItuD , and FenD . The cell-free culture filtrate and extracellular lipopeptide extract of B. subtilis DHA41 demonstrated significant inhibitory effects on the mycelial growth of Fon , Didymella bryoniae , Sclerotinia sclerotiorum , Fusarium graminearum , and Rhizoctonia solani . The lipopeptide extract showed emulsification activity and inhibited Fon mycelial growth by 86.4% at 100 µg/mL. Transmission electron microscope observations confirmed that the lipopeptide extract disrupted Fon cellular integrity. Furthermore, B. subtilis DHA41 emitted volatile organic compounds (VOCs) that exhibited antifungal activity against Fon , D. bryoniae , S. sclerotiorum , and F. graminearum . These findings provide evidence that B. subtilis DHA41 possesses broad-spectrum antifungal activity against different fungi pathogens, including Fon , through the production of extracellular lipopeptides and VOCs.