Abstract:Menaquinone-7 (MK-7) is one of the significant components of vitamin K2. Previous studies found that the highest yield of MK-7 under shake flask culture condition was much higher than that cultured under stirred tank reactor (STR). In order to reduce the differences caused by scaling up from the shake flask to 3 L STR, computational fluid dynamics (CFD) and dynamic absorption method were used to compare the shear stress and oxygen transfer performance of the shake flask and STR at different rotational speeds. The effects of oxygen supply and shear stress on the growth of BS20 and the synthesis of MK-7 were also explored. The results showed that sufficient oxygen supply could promote the growth of BS20 and the synthesis of MK-7, however, excessive shear stress would destroy the bacterial cell and reduce the yield of MK-7. Based on the above results, under the culture condition of the 3 L STR, the lower stirring speed (400 r/min) was used to ensure low shear force, while the oxygen-enriched air (oxygen volume fraction 55%) was used to improve the oxygen supply level. The yield of MK-7 reached 296 mg/L, which was an increase of 152% compared to the control batch (with an oxygen volume fraction of 21%), and reached 79% of the highest level cultured in shake flask. In this study, reducing the stirring speed and increasing the oxygen volume fraction of the supplied air in the STR can effectively improve the performance of the shear-sensitive but highly aerobic fermentation process.
