Antifungal mechanism of bacillomycin D from Bacillus velezensis HN-2 against Colletotrichum gloeosporioides Penz.

Anthracnose is a leaf spot, blossom blight, or fruit rot disease caused by Colletotrichum gloeosporioides (Penz.). It is the most prevalent disease in mango-growing countries worldwide. Lipopeptides, such as those in the iturin family, account for the majority of antifungal secondary metabolites in Bacillus subtilis, Bacillus amyloliquefaciens and Bacillus velezensis, and includes bacillomycin D. Thus far, the mechanism of bacillomycin D's activity has not been clear. In this study, bacillomycin D was isolated from B. velezensis HN-2, which strongly inhibits C. gloeosporioides (Penz.). The median inhibitory concentration of bacillomycin D was 2.162 µg/mL, causing deformation and damage to C. gloeosporioides (Penz.). Bacillomycin D showed more potent activity against C. gloeosporioides (Penz.) than two common fungicides prochloraz and mancozeb. Scanning and transmission electron microscopy revealed that bacillomycin D could injure the cell wall and cell membrane of the hyphae and spores of C. gloeosporioides (Penz.), and the cytoplasm and organelles inside the cell were exuded and formed empty holes. This research clarifies the mechanism underlying bacillomycin D antifungal activity and reveals its high potential as a biopesticide to control phytopathogens.

Volatile organic compounds of Bacillus atrophaeus HAB-5 inhibit the growth of Colletotrichum gloeosporioides.

The use of fungicides to control plant diseases creates a potential health risk. One alternative to this problem is the biological control, which has been succesfully applied to control plant diseases. Bacillus atrophaeus HAB-5 exhibits a high inhibitory acitivities against different fungal pathogens and suppresses them. The aim of current studies is to produce and identify the antifungal compounds produced by the strain HAB-5. We found that the submerge fermentation harvested from Luria-Bertani (LB) medium had the highest activity against Colletotrichum gloeosporioides. The petroleum ether crude extract was strongly bioactive and its activity was stable after heat treatment, pH treatment, illuminated light as well as ultra violet exposition. The antifungal compounds were purified using gel chromatography column. Based on Gas Chromatography-Mass Spectrometry (GC-MS) analysis, nineteen different volatile organic compounds (VOCs) were identified included the range of alkanes, alkenes, alcohols, and organics acid. Among these identified compounds, Chloroacetic acid, tetradecyl esters followed by Octadecane and Hexadecanoic acid, methyl ester showed antifungal activity against C. gloeosporioides. Our results clearly showed Chloroacetic acid, tetradecyl esters; Octadecane and Hexadecanoic acid, methyl ester are key inhibitory compounds produced by Bacillus atrophaeus HAB-5 against C. gloeosporioides.