For the co-production of lactic acid and succinic acid,the effect of redox potential regulation on the fermentation process of Corynebacterium crenatum was studied and the metabolic flux distribution was also analyzed.When the redox potential level was changed from-56 to-400 mV,the concentration of succinic acid in the fermented broth increased from 14 to 20.2 g/L;meanwhile,the concentration of lactic acid decreased from 44.9 to 35.2 g/L.The results of metabolic flux analysis indicated the metabolic flux distribution at the glucose 6-phosphate and phosphoenolpyruvate nodes were affected significantly.Compared with the value obtained at-56 mV,the flux ofpentose phosphate pathway (HMP) pathway increased by 2.74 fold and the flux from phosphoenolpyruvate to oxaloacetate increased by 78％.As a result,the flux of succinic acid increased from 31.73 to 56.53 mmol/(L·g·h) and the flux of lactic acid decreased from 159.73 to 133.50 mmol/(L·g·h).The results of this study demonstrated that glucose 6-phosphate and phosphoenolpyruvate were the key nodes that could affect the production of succinic acid by C.crenatum fermentation under anaerobic conditions,which has contributed to the co-production of lactic acid and succinic acid by manipulating wild-type C.crenatum to change the ratio of succinic acid/lactic acid through metabolic engineering.
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