Strain mutagenesis and initial conditions of solid-state fermentation soybean meal using Bacillus subtilis (ACCC 01746)Author(s): Hai-Cheng Yin
To enhance the protease activity effectively, during the solid-state fermentation (SSF) the Bacillus subtilis ACCC 01746 (B. subtilis) exhibiting protease secretion ability was irradiated by the 10-30 mW output power and 10-30 min exposure time under the He-Ne laser with a wavelength ë = 632.8 nm and laser beam 1.3 mm in diameter, respectively. The optimum irradiation dosages were obtained at the 20 mW output power and 20 min exposure time. Upon the optimum mutagenesis conditions, the maximum protease activity of a stable positive mutant strain B. subtilis-3 was obtained, and displayed maximum protease activity in the soybean protein-agar slant medium, 656.88 U/mL, compared with the parent strain, 467.43 U/mL. The SSF with B. subtilis-3 was studied to evaluate the effects of the optimal single-factor conditions on the activity of protease containing the temperature, time, moisture content, inoculum size and pH as initial fermentation conditions for the mutant. The optimum initial conditions of SSF soybean meal and the maximum protease activity respectively were shown at the range, where the temperature, time, moisture content, inoculum size and pH were 34°C, 43 h, 59%, 7% and 6.8, whereas the enzyme activities were 642.61, 658.94, 667.07, 683.73 and 693.45 U/mL for B. subtilis-3, respectively. The results suggest that the mutant B. subtilis-3 SSF soybean meal had beneficial effects on the production of protease.