초록
During a fermentation process, the formation of the desired product during the cell growth phase competes with the biomass for substrates or inhibits cell growth directly, which results in a decrease in production efficiency. A genetic switch is required to precisely separate growth from production and to simplify the fermentation process. The ldhA promoter, which encodes the fermentative d-lactate dehydrogenase (LDH) in the lactate producer Escherichia coli CICIM B0013-070 (ack-pta pps pflB dld poxB adhE frdA), was replaced with the λ p<SUB>R</SUB> and p<SUB>L</SUB> promoters (as a genetic switch) using genomic recombination and the thermo-controllable strain B0013-070B (B0013-070, ldhAp::kan-cI<SUP>ts</SUP>857-p<SUB>R</SUB>-p<SUB>L</SUB>), which could produce two-fold higher LDH activity at 42<SUP>o</SUP>C than the B0013-070 strain, was created. When the genetic switch was turned off at 33<SUP>o</SUP>C, strain B0013-070B produced 10% more biomass aerobically than strain B0013-070 and produced only trace levels of lactate which could reduce the growth inhibition caused by oxygen insufficiency in large scale fermentation. However, 42<SUP>o</SUP>C is the most efficient temperature for switching on lactate production. The volumetric productivity of B0013-070B improved by 9% compared to that of strain B0013-070 when it was grown aerobically at 33<SUP>o</SUP>C with a short thermo-induction at 42<SUP>o</SUP>C and then switched to the production phase at 42<SUP>o</SUP>C. In a bioreactor experiment using scaled-up conditions that were optimized in a shake flask experiment, strain B0013-070B produced 122.8g/l d-lactate with an increased oxygen-limited productivity of 0.89g/g.h. The results revealed the effectiveness of using a genetic switch to regulate cell growth and the production of a metabolic compound.