Objective  Taxonomy of antimicrobial protease-producing Cytobacillus kochii H was studied for the development of a natural disease control agent on plants.

  Method   Taxonomy of C. kochii H was determined by physiological, biochemical, electron microscopy scanning, and 16sRNA sequencing methods. A process of producing the antimicrobial protease secreted by the bacterium was optimized in single-factor and orthogonal experiments. The efficacy of the culture broth on 4 selected pathogenic fungi was applied in an in vitro test as the evaluation criterium.

  Result   The optimized C. kochii H protease-producing process was conducted in a 250 mL triangular flask using 50 mL of pH 8.0 medium, which contained 20.0 g·L⁻¹ of glucose, 8.0 g·L⁻¹ of peptone, 1.0 g·L⁻¹ of MgSO₄, and 0.1g·L⁻¹ of CaSO₄-2H₂O, inoculated with 2.5 mL of 10⁸ CFU·mL⁻¹ C. kochii H fermentation liquid. After 24 h of incubation, the protease activity reached 402.2 U·mL⁻¹, which was 13.92 times greater than it was prior to the optimization. The antimicrobial rates of the broth against Fusarium oxysporum and Phytophthora capsici were 67.32% and 44.87%, respectively, i.e., 9.15% and 12.82%, respectively, increases over those before the optimization.

  Conclusion  The antimicrobial protease-producing C. kochii H was identified taxonomically. The culture process of the enzyme production was optimized to deliver significant in vitro inhibition rates on F. oxysporum and P. capsici.