Isolation and Identification of Antibacterial Lpopeptides from Bacillus subtilis KC-WQ Fermentation Broth and Optimization of Fermentation Conditions

This paper studied the antibacterial effect and functional components of the extracellular secretions of a strain of Bacillus subtilis KC-WQ. The experiment found that KC-WQ had obvious antibacterial effect on Escherichia coli, Salmonella enterica subsp. enterica and Aeromonas hydrophila, among which it had the most significant antibacterial effect on Salmonella. On this basis, the acid precipitation method was used to separate the antibacterial components, and the structure was found through thin layer chromatography (TLC), high performance liquid chromatography (HPLC) and matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS). The antibacterial substances secreted by this strain were lipopeptides with a molecular weight distribution between 1030.5 and 1491.4 Da, mainly composed of Iturin, Surfactin and Fengycin, and the minimum inhibitory concentration was 0.8 mg/mL. The lipopeptide component still maintained a good antibacterial effect after heat treatment (105 ℃, 20 min). The response surface method was used to optimize the culture conditions of KC-WQ, and the best fermentation conditions were obtained: The initial pH was 6.0, the fermentation temperature was 36 ℃, the shaker speed was 208 r/min, and the predicted crude product yield was 1.311 g/L. Later verified by experiments, the actual yield was 1.236 g/L. The above results indicated that Bacillus subtilis KC-WQ had good antibacterial and processing properties, could be used as a good antibacterial ingredient, and had a good application prospect in the development of antibacterial and preservation materials in food industry.