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

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.

Suppressive biomasses and antagonist bacteria for an eco-compatible control of Verticillium dahliae on nursery-grown olive plants

“…and Burkholderia cepacia (Gram-), respectively, were used in the following tests in vitro and in vivo. This choice was also supported by previous studies where these two antagonists were tested as biocontrol agents against other fungal pathogens and characterized by their mechanisms of action (i.e., production of antifungal metabolites) (De Curtis et al 2010;Vitullo et al 2012).…”

“…These results confirm the authors' previous findings (Vitullo et al 2008) where filtrates of isolate BO7 were more effective in inhibiting fungal pathogens than filtrates of isolate BTd1. This result is probably due to the capacity of BO7 to produce high amounts of antifungal lipopeptides of the surfactin family displaying a strong inhibitory activity in vitro (Vitullo et al 2012). The untreated water extracts of OMW-M1 and OMW-M2 inhibited the pathogen growth by about 65 and 76 %, respectively.…”

“…To this aim, a drop (5 ll) of V. dahliae conidial suspension in sterile distilled water was placed in the centre of the plate and, subsequently, a drop (5 ll) of each bacterial strain in PBS containing 1 9 10 9 cells was placed at 30 mm from V. dahliae microconidial drop. Plates were incubated at 28°C and, after different time periods (3, 5, 7, 10, and 16 days), the radius of the developed fungal colony was measured in each plate (Vitullo et al 2012).…”

HapX-Mediated Iron Homeostasis Is Essential for Rhizosphere Competence and Virulence of the Soilborne Pathogen Fusarium oxysporum

“…Briefly, 2-week-old seedlings of tomato cv Monika were inoculated with F. oxysporum strains by immersing the roots in a microconidial suspension, planted in vermiculite, and maintained in a growth chamber. For bacterial/fungal coinoculation assays, seedlings were first dip-inoculated into a suspension of P. putida strains for 2 h and then infected with F. oxysporum as described above (Vitullo et al, 2011). The severity of disease symptoms and percentage survival were recorded each day for 30 to 45 d. Ten plants were used for each treatment.…”

Enhanced Nutritional Programme: An Innovative Approach to Controlling Plant Diseases in the Tropics

“…were reported to produce antimicrobial secondary metabolites such as phenazines (Thomashow and Weller 1988 ), hydrogen cyanide (Rudrappa et al 2008 ), 2,4-diacetylphloroglucinol (Raaijmakers et al 1997 ), pyrrolnitrin (Howell and Stipanovic 1979 ), pyoluteorin (Howell and Stipanovic 1980 ), cyclic lipopeptides tensin (Nielsen et al 2000 ) and viscosinamide (Nielsen et al 1999 ), while Bacillus spp. were reported to produce antifungal activity compounds such as surfactins (Vitullo et al 2012 ) and kurstakins (Bechet et al 2012 ). BCAs also help by inducing systemic resistance (ISR) and systemic acquired resistance (SAR) responses through root-to-shoot long-distance intra-plant signaling, priming plants to better resist against pathogen attack (van Loon 2007 ).…”