Enhancement of  l‐phenylalanine production in Escherichia coli by heterologous expression of Vitreoscilla hemoglobin

Abstract l ‐Phenylalanine is an important amino acid that is widely used in the production of food flavors and pharmaceuticals. Generally, l ‐phenylalanine production by engineered Escherichia coli requires a high rate of oxygen supply. However, the coexpression of Vitreoscilla hemoglobin gene ( vgb ), driven bya tac promoter, with the genes encoding 3‐deoxy‐ d ‐arabinoheptulosonate‐7‐phosphate synthetase ( aroF ) and feedback‐resistant chorismate mutase/prephenate dehydratase ( pheA fbr ), led to increased productivity and decreased demand for aeration by E. coli CICC10245. Shake‐flask studies showed that vgb ‐expressing strains displayed higher rates of oxygen uptake, and l ‐phenylalanine production under standard aeration conditions was increased. In the aerobic fermentation process, cell growth, l ‐phenylalanine production, and glucose consumption by the recombinant E. coli strain PAPV, which harbored aroF , pheA fbr , and tac‐vgb genes, were increased compared to that in the strain harboring only aroF and pheA fbr ( E. coli strain PAP), especially under oxygen‐limited conditions. The vgb ‐expressing strain PAPV produced 21.9% more biomass and 16.6% more l ‐phenylalanine, while consuming only approximately 5% more glucose after 48 H of fermentation. This study demonstrates a method to enhance the l ‐phenylalanine production by E. coli using less intensive and thus more economical aeration conditions.