Effect of Transport Proteins SstT and RhtC Modification on L-threonine Production in Escherichia coli
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Abstract:
L-threonine is an essential amino acid and has wide application in food, pharmaceutical and feed fields. It has been reported that the reduction of the intracellular L-threonine concentration could remove the feedbacks on the enzymes in L-threonine synthetic pathway, which was benefit for L-threonine production. Hence, in this work, gene sstT was deleted in E. coli TRFC, an L-threonine producer, by Red recombination technology and gene rhtC was over expressed in TRFCΔsstT. Compared to the control strain TRFC, TRFCΔsstT was found to produce 4% more L-threonine. And compared to TRFCΔsstT+pSTV28，TRFCΔsstT+pSTV28-rhtC produced 18.16% more L-threonine in shake flask fed-batch fermentation. Besides, the intracellular L-threonine concentrations of all mutants were lower than the control strains. Finally, in the 5 L fed-batch fermentation, L-threonine production and yield on glucose of TRFCΔsstT+pSTV28-rhtC were 15.33% and 16.14% higher than those of TRFC, respectively. The results suggested that modification of transport system could effectively decrease the intracellular L-threonine concentration and enhance the excretion of internal synthesized L-threonine, and could be benefit for L-threonine production.
