中国生物工程杂志

The effects of six vitamins on a novel isolate, Corynebacterium glutamicum SYPS-062, which could directly produce L-serine from carbohydrates were investigated. These vitamins play the important roles in the L-serine metabolic pathway. By comparing the L-serine production, biomass accumulation, transformation efficiency (YP/S) and L-serine yield per biomass (YP/X), the L-serine metabolic regulation mechanism by each vitamin was analyzed. and the results show that all these tested vitamins－VB1, biotin，VB2，VB6，folate and VB12 could enhance the growth of C. glutamicum SYPS-062 and improve the production of L-serine, however, the mechanisms of their metabolic regulations were different. The obvious decrease of YP/S and YP/X reflected that the addition of VB1 and biotin caused more L-serine to degrade to pyruvate by accelerating the transformation of pyruvate to TCA circle, and the promotion of VB6 on L-serine degradation was more remarkable than the synthesis, but the significant increase of biomass led to the increment of the total L-serine production by adding above three vitamins, which was 31%，28% and 11% higher than the control; VB2 could improve both the biomass (35%) and the L-serine production (33%) equally, due to the promotion of the energy metabolism, and thus it does not influence the flux distribution of metabolic pathway of L-serine; Folate and VB12 are the carriers of the one carbon units, trace folate and VB12 could diminish L-serine degradation flux ratio which was directed into glycine and one carbon uint, and increased YP/S and YP/X by accelerating the efficiency of the one carbon units metabolism. The final L-serine productions were 7.1 g/L and 9.7 g/L, which were 39% and 82% higher than the control. These results conform that L-serine is an important intermediate metabolite of C. glutamicum SYPS-062. Moreover, by manipulating these 6 vitamins levels, the distribution of metabolic flux can be discovered and regulated, which is an effective strategy to increase the production of L-serine. Finally, the fermentation period was 6 h shorter by adding all these vitamins at their optimal doses than by adding biotin only, and the accumulation of L-serine and the biomass were 9.0 g/L and 11 g/L, which were 70% and 76% higher than the control.