No abstract

Three new lipopeptides (1-3) were isolated from the organic extract of Bacillus amyloliquefaciens strain (BO7). These compounds represented the major constituents (>60%) of the total cell lipids extractable with CHCl(3)/MeOH (2:1). Elucidation of their chemical structure was carried out by spectroscopic analyses, including 1D and 2D NMR spectroscopy, mass spectrometry (MS), and secondary ion mass spectrometry (MS/MS), along with chemical degradation. The compounds are members of the surfactins family and are based on the heptapeptide Glu-Leu-Leu-Ala-Asp-Leu-Leu, N-acylated to the N-terminal by an (R)-3-hydroxy fatty acid with linear alkyl chains from 16:0 to 18:0 (1-3, respectively). An ester bond between the 3-hydroxyl group of the fatty acid and the carboxylic group of the C-terminal amino acid closes a 13-membered lactone ring. The bacterial lipopeptides, particularly compound 3, displayed strong and dose-dependent antifungal activity against the plant pathogenic fungus Fusarium oxysporum.

No abstract

No abstract

The aim of this work was to investigate the major mechanisms involved in antagonism of BO7, a novel strain of Bacillus amyloliquefaciens isolated from orchard soil, against the vascular wilt fungus Fusarium oxysporum f. sp. lycopersici (Fol). BO7 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 BO7 cells to adhere to fungal hyphae and to efficiently colonize tomato roots. The low molecular weight fraction of BO7 culture filtrate displayed high antifungal activity against Fol, resulting in growth inhibition and dramatic alterations of hyphal morphology. Three structurally related surfactin 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 BO7 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.