Role of new bacterial sorfactins in the antifungal interaction between Bacillus amyloliquefaciens and Fusarium oxysporum

摘要

The aim of this work was to investigate the major mechanisms involved in antagonism of B07, a novel strain of Bacillus amyloliquefaciens isolated from orchard soil, against the vascular wilt fungus Fusarium oxysporum f. sp. lycopersici (Fol). B07 markedly reduced the incidence of Fol vascular wilt on tomato plants and displayed strong in vitro inhibitory activity against Fol. Scanning electron microscopy demonstrated the ability of B07 cells to adhere to fungal hyphae and to efficiently colonize tomato roots. The low molecular weight fraction of B07 culture filtrate displayed high antifungal activity against Fol, resulting in growth inhibition and dramatic alterations of hyphal morphology. Three structurally related surfac-tin lipopeptides, identified as the major components of the bioactive fraction, were assayed for their inhibitory activity against Fol. One of these compounds exerted a strong and uncommon antifungal activity for lipopeptides of the surfactin family, accounting for most of the inhibitory activity of the B07 culture filtrate. Among a collection of Fol knockout isolates tested, mutants altered in cell wall structure showed increased sensitivity to the bacterial compounds. These results suggest that the fungal cell wall might have a key role in the sensitivity of Fol towards bacterial surfactins from B. amyloliquefaciens.