ESI LC-MS and MS/MS characterization of antifungal cyclic lipopeptides produced by Bacillus subtilis XF-1.

Bacillus subtilis XF-1 (CGMCC No. 2357), a patent strain with good effects for controlling the clubroot of crucifer and many pathogenic fungi, was predicted to produce cyclic lipopeptide (CLP) antibiotics based on its genomic analysis. In this study, the CLPs were purified and determined with the following protocol: the supernatant of XF-1 cultivating mixture was firstly precipitated, then the precipitants were extracted with methanol and further separated by Sephadex LH-20 chromatography to test its antifungal activities. Fungi-inhibiting fractions were further characterized with LC/ESI-MS and LC/ESI-MS/MS. The results show that four molecular ion peaks [M+H]⁺ (m/z 1,464, 1,478, 1,492 and 1,506) from fungi suppression fraction were identified as fengycin A with fatty acid of C₁₆-C₁₉, fengycin B (C₁₄-C₁₇), fengycin C (C₁₅-C₁₈), fengycin D (C₁₅-C₁₈) and fengycin S (C₁₅-C₁₈). Fengycin C (C₁₅ and C₁₈), fengycin D (C₁₅, C₁₆ and C₁₈) and fengycin S (C₁₅, C₁₆ and C₁₈) were reported for the first time. The diversity of the fengycins that exist in this strain will help the elucidation of their biocontrol mechanisms.