Abstract: Cell suspension turbidity (optical density at 660 nm, OD660 nm) was measured using an automated growth curve analyzer to investigate the growth of Bacillus subtilis natto during incubation in a liquid culture medium composed of soybean meal as nitrogen source and glucose as carbon source. The optimal concentrations of soybean meal and glucose were found to be 50 g/L and 10 g/L, respectively. Using one-factor-at-a-time combined with orthogonal array design method, temperature, pH and time were identify as major factors that influence the growth of Bacillus subtilis natto. Further, Box-Behnken experimental design was used to optimize the main influencing factors. Bacillus subtilis natto achieved the highest biomass after 13 h of incubation at initial pH 6.16 and 35.5 ℃ in the presence of soybean meal treated by ultrasonic for 4.32 min, and the cell suspension turbidity was 1.635 under these conditions.

Key words: Bacillus subtilis natto, soybean meal, orthogonal array design, Box-Behnken experimental design