Objective   Fermentation of Bacillus velezensis FJ17-4 known with a high inhibitory activity against several pathogens was optimized for potential application as a biocontrol agent.

  Methods   Spectrometric measurement at OD₆₀₀ of the fermentation broth was used as the index for evaluation. Culture medium and conditions were optimized by single factor and orthogonal experiments. Bacterial quantity, pathogenic inhibition, and indoor potted control effect of the optimized fermentation product were determined.

  Results   The optimized FJ17-4 fermentation used a medium that consisted of 12.5 g·L⁻¹ soybean meal, 5.0 g·L⁻¹ corn flour, and 12.5 g·L⁻¹ potassium dihydrogen phosphate at an initial pH of 7.0 to ferment a liquid loading (medium volume) of 50 mL with an inoculum size of 12.5% for 40 h at 30 ℃ in a 250 mL flask that rotated at a constant speed of 180 r·min⁻¹. The OD₆₀₀ of the optimized fermentation broth was 1.52 representing a cell load of 1.03×10¹⁰ cfu·mL⁻¹, which were 25.62% and 21.95%, respectively, higher than those prior to the optimization. The inhibition rate on the mycelial growth of Fusarium oxysporum f. sp. cucumerinum and the indoor potted control on cucumber fusarium wilt of the 50× optimized fermentation broth were 42.35% and 72.14%, representing 56.38% and 13.46% increases, respectively, over the original.

  Conclusion   The FJ17-4 fermentation was significantly improved by the optimization. An operational cost reduction was also achieved.