RESUMO
In order to investigate the effect of malic enzyme on anaerobic mixed acid fermentation,the gene encoding NAD+-dependent malic enzyme was amplified from E.coli DH5? genome by using PCR and cloned into vector pTrc99a to give an expression vector pTrc99a-sfcA.Malic enzyme was overproduced by E.coli FMJ39(ldh,pfl)harboring pTrc99a-sfcA under the condition of IPTG induction.The results of anaerobic fermentation indicated overexpression of malic enzyme would have influence on the pathway of formate,acetate and succinate of FMJ39.The concentration of formate and acetate was 17.58% and 15.27% higher than FMJ39,the succinate concentration was reduced by 26.87%.There was no obvious citrate concentration change.The experimental results also indicated that high concentration of L-Thr and L-Ser would induce the Tdc operon to convert pyruvate into formate and acetate even when pfl gene encoding the pyruvate formate lyase was inactivated.
