Antifungal activity and functional components of cell-free supernatant from <i>Bacillus amyloliquefaciens</i> LZN01 inhibit <i>Fusarium oxysporum</i> f. sp. <i>niveum</i> growth

<i>Bacillus amyloliquefaciens</i> LZN01 shows antagonistic behaviour against <i>Fusarium oxysporum</i> f. sp. <i>niveum</i> (<i>Fon</i>). This study aimed to analyze the antifungal activity and the functional components of cell-free supernatant from <i>B. amyloliquefaciens</i> LZN01 that inhibited <i>Fon</i> growth. The results showed that the cell-free supernatant (CFS) from the death phase had stronger antifungal activity against <i>Fon</i> compared to those from the exponential stage and stationary phase. The analyses from scanning and transmission electron microscopy demonstrated that treatment with CFS led to cellular morphological changes, including concave formations on the conidial surface, the disruption of cell walls and membranes, the leakage of intracellular contents and the aggregation of organelles. Confocal laser scanning microscopy revealed that the CFS damaged membrane integrity. Myriocin, sphingofungin E, sphingofungin F, 3-methyl-2-oxovaleric acid, gabapentin and sphingofungin C were confirmed as the major differential metabolites by ultra-high-performance liquid chromatography-LTQ orbitrap (UHPLC-LTQ Orbitrap) MS analysis. Quantitative analysis showed that the myriocin content in the CFS was 0.6 μg/mL, and its minimum inhibitory concentration (MIC) was 1.25 μg/mL. It can be speculated that some antifungal compounds in the CFS, including myriocin, sphingofungin E, sphingofungin F and sphingofungin C, play major roles in inhibiting the growth of <i>Fon</i> and the synergistic effects among these antifungal compounds are important in suppressing <i>Fon</i> reproduction. This study suggests that <i>B. amyloliquefaciens</i> LZN01 is a promising biological agent against <i>Fon</i> as its CFS exerts antifungal activity by deforming conidial structures and damaging membranes and myriocin was one of the major functional components of the CFS.