© 2016 Hou et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Phenylpyruvic acid (PPA) is widely used in the pharmaceutical, food, and chemical industries. Here, a two-step bioconversion process, involving growing and resting cells, was established to produce PPA from L-phenylalanine using the engineered Escherichia coli constructed previously. First, the biotransformation conditions for growing cells were optimized (L-phenylalanine concentration 20.0 g·L -1 , temperature 35°C) and a two-stage temperature control strategy (keep 20°C for 12 h and increase the temperature to 35°C until the end of biotransformation) was performed. The biotransformation conditions for resting cells were then optimi zed in 3-L bioreactor and the optimized conditions were as follows: agitation speed 500 rpm, aeration rate 1.5 vvm, and L-phenylalanine concentration 30 g·L -1 . The total maximal production (mass conversion rate) reached 29.8 ± 2.1 g·L -1 (99.3%) and 75.1 ± 2.5 g·L -1 (93.9%) in the flask and 3-L bioreactor, respectively. Finally, a kinetic model was established, and it was revealed that the substrate and product inhibition were the main limiting factors for resting cell biotransformation.
Hou, Y., Hossain, G. S., Li, J., Shin, H. D., Liu, L., Du, G., & Chen, J. (2016). Two-step production of phenylpyruvic acid from L-phenylalanine by growing and resting cells of engineered Escherichia coli: Process optimization and kinetics modeling. PLoS ONE, 11(11). https://doi.org/10.1371/journal.pone.0166457