Abstract:To further improve the ability of Bacillus subtilis natto to synthesize vitamin K2, the effect of rotational speed(0、200 r/min) on cell growth and product formation was investigated in 250 mL shake flasks. A two-stage rotational speed control strategy was proposed by analyzing the fermentation process curves and kinetic parameters under different conditions, as well as by observing the morphological changes between the bacteria at different time points after diluting and coating the fermentation broth with scanning electron microscopy. The conditions (temperature, speed, pH and time) affecting the control strategy were optimized by orthogonal design. When the rotate speed was maintained at 0 r/min, the highest yield of vitam in K2 was obtained at 108 h and the morphology of bacteria was mostly folded at the later stage of fermentation. When the rotate speed was maintained at 200 r/min, the biomass was higher than that at 0 r/min. The bacteria were broken at the later stage of fermentation, and a few of them had a smooth surface. After optimization, the yield of vitamin K2 reached （35.6±0.13） mg/L at 40 ℃ and pH 6.5 when the rotate speed was maintained at 200 r/min from 0 h to 36 h, and maintained at 0 r/min from 36 h to 132 h, which was 1.67 times and 9.674 times higher than that before optimization (0、200 r/min), respectively. The stage-by-stage control of rotational speed could effectively improve the ability of Bacillus subtilis natto to synthesize vitamin K2, which is of great guiding significance and reference value for the large-scale production of vitamin K2.
