Antifungal activity of lipopeptides from Bacillus pumilus against soybean phytopathogens: chemical characterisation and ultrastructural alterations

Soybean cultivations are frequently affected by fungal diseases that adversely influence productivity. Bacteria of the Bacillus genus have been widely employed as an alternative method to control fungal infections. This work evaluated the antifungal potential of lipopeptides produced by Bacillus pumilus against seven important soybean phytopathogenic fungi: Colletotrichum truncatum, Corynespora cassiicola, Diaporthe longicolla, Diaporthe ueckeri, Fusarium incarnatum-equiseti, Fusarium graminearum, and Macrophomina phaseolina. Lipopeptides extracted from the fermented broth of B. pumilus were characterised by electrospray ionisation high-resolution mass spectrometry (ESI-HRMS/MS) and nuclear magnetic resonance (1H NMR). Three surfactin isoforms (C13, C14, and C15) were identified. The lipopeptide extract (5 mg/mL) inhibited mycelial growth of all the fungi tested. Scanning electron microscopy revealed severe ultrastructural damage to the fungi, including wilting and twisting of hyphae, spore deformation, and reduced formation of resistance structures. In conclusion, the surfactin-rich B. pumilus extract has high potential for controlling soybean phytopathogens, as a promising alternative strategy in integrated pest and disease management programmes.