The directed modification of Escherichia coli MG1655 to obtain histidine-producing mutants

Strain MG1655+ hisG r hisL′-ΔΔ, purR, which produces histidine with a weight yield of approximately 12% from glucose, was constructed through directed chromosomal modifications of the laboratory Escherichia coli strain MG1655+, which has a known genome sequence. A feedback-resistant ATP-phosphoribosyl transferase encoded by the mutant hisG r (E271K) was the main determinant of histidine production. A further increase in histidine production was achieved by the expression enhance of a mutant his operon containing hisG r through the deleting attenuator region (hisL′-Δ). An increase in the expression of the wildtype his operon did not result in histidine accumulation. Deletion of the transcriptional regulator gene purR increased the biomass produced and maintained the level of histidine production per cell under the fermentation conditions used.