Surfactin-Induced β-(1,3)-Glucan Exposure in Aspergillus niger Cell Wall: A Molecular Perspective

Fruit spoilage caused by fungal pathogens jeopardizes food safety and inflicts significant economic damage. Cyclic lipopeptides (CLPs) have been applied as biofungicides by disrupting the cell membrane and intracellular components; however, the first target for antifungal action is the fungal cell wall. This study elucidates the molecular mechanism by which CLPs compromise cell wall integrity using molecular dynamics simulation and experimental validation. Among Surfactin C, Iturin A, and Fengycin A, Surfactin C exhibited the strongest binding to β-glucan (ΔE = -1970.536 kcal/mol) and the lowest free volume (7.302%), with enhanced effects at higher concentrations. Key interaction sites were identified at C=O of D-Leu3, -N-H of Leu2, and -COOH of Glu1 by Radial distribution function. In vivo assays with Aspergillus niger confirmed a MIC of 40 µg/mL and Surfactin-induced β-glucan exposure. FTIR and XPS analyses revealed structural reorganization and hydrogen bonding, while SEM/TEM showed spore deformation and wall rupture. These findings demonstrate that Surfactin disrupts fungal cell walls via direct complexation with β-glucan, leading to structural collapse and cell death, supporting its potential as a targeted biofungicide.