Characterization of lipopeptides produced by Bacillus licheniformis FJAT-4 and their effect on Fusarium oxysporum

Abstract:

[Objective] Lipopeptides produced by Bacillus licheniformis FJAT-4 can strongly inhibit the mycelia growth of Fusarium oxysporum. The aim of this study was to identify the structure of antifungal lipopeptide, analyze the effect of culture medium and temperature on the antifungal lipopeptide production, and explain antifungal effect of lipopeptide against F. oxysporum. This study is helpful to understand the mechanisms of Bacillus licheniformis FJAT-4 in controlling F. oxysporum.[Methods] Crude lipopeptides were extracted by acid precipitation and resolved in methanol. Their structures were identified using liquid chromatography coupled with quadrupole time-of-flight tandem mass spectrometry. Their antifungal activities were determined through the assay of inhibition zone experiment. Their effects against F. oxysporum were observed using scanning electron microscopy.[Results] Lipopeptides produced by B. licheniformis FJAT-4 were identified as C₁₇ fengycin A, C₁₇ fengycin B, C₁₇ fengycin B₂, C₁₆ fengycin A variant, C₁₆ fengycin B variant, C₁₃-C₁₅ surfactin and C₁₃-C₁₅ surfactin variants. Among them, C₁₃-C₁₅ surfactin variants with m/z 1048.6/1062.6/1076.6 were new compounds. Results showed that the culture mediums have relatively little influence on the composition of lipopeptides produced by FJAT-4. However, the culture temperature presented obviously impact on the production of antifungal lipopeptides, which can only be produced by strain FJAT-4 growing at higher temperature (30-40℃) in comparison to temperature between 20-25℃. The higher culture temperature was in favour of increasing the proportion of surfactins in lipopeptide mixture. The lipopeptides exhibited strong antifungal activity against several plant pathogenic F. oxysporum strains in a dosage-dependent mode. Observation under scanning electron microscopy showed that the antagonistic lipopeptides secreted by B. licheniformis FJAT-4 significantly led to abnormal mycelia and spore growth of F. oxysporum.[Conclusion] The lipopeptides produced by FJAT-4 was composed of fengycins and surfactins. These lipopeptides display strong antifungal activity against several strains of plant pathogenic F. oxysporum, and destroyed the mycelial structure of the pathogenic F. oxysporum.