Exploring Mechanisms of Antifungal Lipopeptide Iturin A from Bacillus against Aspergillus niger

The control of Aspergillus niger (A. niger) is of great significance for the agricultural economy and food safety. In this study, the antifungal effect and mechanism of iturin A from Bacillus amyloliquefaciens (CGMCC No. 8473) against A. niger (ATCC 16404) were investigated using biochemical analyses and proteomics. Changes in a mycelium treated with iturin A were observed using scanning electron microscopy and transmission electron microscopy, including mycelial twisting and collapse, organelle disintegration, and intracellular vacuolization. The cytomembrane integrity of A. niger was affected by iturin A, as detected by propidium iodide staining. In addition, the generation of excess reactive oxygen species, the hyperpolarization of the mitochondrial membrane potential and malondialdehyde accumulation also indicated that iturin A induced apoptosis in A. niger through the oxidative stress pathway. Proteomics results showed that 310 proteins were differentially expressed in the A. niger mycelium exposed to iturin A, including 159 upregulated proteins and 151 downregulated proteins, which were mainly associated with energy metabolism of A. niger. We propose that iturin A might inhibit the growth of A. niger by disrupting cytomembrane integrity, via oxidative stress, and by interfering with glycolysis/gluconeogenesis and the tricarboxylic acid cycle. Overall, iturin A is a promising antifungal agent that provides a rationale for controlling A. niger contamination in food.