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Optimization of the Fermentation Medium and Analysis of the Compositions of Antifungal Compounds from Bacillus malacitensis Z-5
Authors:Gao Yu  Chen Yaoyao  Liu Yijie  Chen Xiaomeng  Gao Tongguo  Zhang Dongdong
Affiliation:College of Life Sciences/ Hebei Agricultural University, Baoding, Hebei 071001, China
Abstract:[Objective] Bacillus malacitensis Z-5 has a significant biocontrol effect on cotton Verticillium wilt mainly through its production of antifungal substances. This study aimed to optimize the culture medium’s composition. Additionally, it aimed to identify the genes that produce the antifungal substances and determine the components of these antifungal substances. [Methods] Single factor tests were used to determine the optimal carbon and nitrogen sources, as well as the inorganic salt level. The most rapid rise method was used to determine the carbon and nitrogen sources and the inorganic salt’s optimal content area. Box–Behnken response surface methodology was applied, and the composition of the medium that produced the optimum level of antifungal substances was determined using antifungal activity as the screening index. The composition of the antifungal substances and the related genes from the Z-5 strain were identified using liquid chromatography-mass spectrometry and polymerase chain reaction, respectively. [Results] The optimal medium for the generation of antifungal substances by the Z-5 strain consisted of 2.68% (mass fraction) corn flour, 1.45% yeast powder, 0.03% K2SO4, 0.8% Na2HPO4·12H2O, and 0.2% NaH2PO4·2H2O at pH 7.2–7.4. The antifungal zone was 1.34 cm in diameter, which was close to the predicted value, confirming that the model was reliable and effective. Antifungal substances were mainly lipopeptide antibiotics C14 surfactin B, C14–C17 iturin A, and C14, C15, and C17 iturin B. polymerase chain reaction revealed that srfAB, ituC, and ituD occur in the Z-5 genome. [Conclusion] This study optimized the culture medium for producing antifungal substances, which are composed of lipopeptide antibiotics, from the B. malacitensis Z-5 strain. The results provide a theoretical reference and material basis for the prevention of cotton Verticillium wilt using these antifungal substances.
Keywords:cotton Verticillium wilt  Bacillus malacitensis  antagonistic  lipopeptide antibiotics  response surface analysis   fermentation conditions  
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