Cyclic lipopeptides were produced by Bacillus amyloliquefaciens subsp. plantarum strain BC32-1 that was isolated from yellow loess soil in the Jeonnam province of South Korea. Several lipopeptides were isolated from the bacteria using organic solvent extraction and reverse-phase high-performance liquid chromatography (RP-HPLC). Purified iturin-, surfactin-, and fengycin-type lipopeptides were identified using liquid chromatographymass spectrometry (LC-MS) analysis. Among the lipopeptides, C 17 -fengycin B showed strong antifungal activity against the phytopathogenic fungus, Fusarium oxysporum f. sp. radicis-lycopersici, and then the fengycin was further characterized by UV, Fourier transform-infrared spectroscopy (FT-IR), and LC-MS/MS analyses. C 17 -fengycin B was highly produced at quantities of up to 15 µg/mL at 37 o C, whereas little amount of the fengycin was produced at 25 o C. Purified C 17 -fengycin B inhibited mycelial growth of F. oxysporum with a minimal inhibitory concentration of 50 µg/mL. This study suggests that C 17 -fengycin B is a major antifungal component produced by the BC32-1 strain that could be used as an environmentally friendly agent to control the phytopathogenic F. oxysporum.
Microbial volatiles have beneficial roles in the agricultural ecological system, enhancing plant growth and inducing systemic resistance against plant pathogens without being hazardous to the environment. The interactions of plant and fungal volatiles have been extensively studied, but there is limited research specifically elucidating the effects of distinct volatile organic compounds (VOCs) on plant growth promotion. The current study was conducted to investigate the impact of VOCs from Cladosporium halotolerans NGPF1 on plant growth, and to elucidate the mechanisms for the plant growth-promoting (PGP) activity of these VOCs. The VOCs from C. halotolerans NGPF1 significantly promoted plant growth compared with the control, and this PGP activity of the VOCs was culture medium-dependent. Headspace solid-phase microextraction (HS-SPME) coupled with gas chromatography–mass spectrometry (GC–MS) identified two VOC structures with profiles that differed depending on the culture medium. The two compounds that were only produced in potato dextrose (PD) medium were identified as 2-methyl-butanal and 3-methyl-butanal, and both modulated plant growth promotion and root system development. The PGP effects of the identified synthetic compounds were analyzed individually and in blends using N. benthamiana plants. A blend of the two VOCs enhanced growth promotion and root system development compared with the individual compounds. Furthermore, real-time PCR revealed markedly increased expression of genes involved in auxin, expansin, and gibberellin biosynthesis and metabolism in plant leaves exposed to the two volatile blends, while cytokinin and ethylene expression levels were decreased or similar in comparison with the control. These findings demonstrate that naturally occurring fungal VOCs can induce plant growth promotion and provide new insights into the mechanism of PGP activity. The application of stimulatory volatiles for growth enhancement could be used in the agricultural industry to increase crop yield.
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