Metabolic Engineering and Adaptive Evolution of Escherichia coli for 3-Hydroxypropionate Production Under Low pH Conditions
Metabolic engineering of Escherichia coli for the production of platform chemicals has become an emerging hotspot of industrial biotechnology. 3-hydroxypropionate, which has an active hydroxyl group and a carboxyl group on each terminal of its structure, can participate in many chemical reactions and be derived into many important chemicals. Biological production of 3-hydroxypropionate by metabolic engineering of Escherichia coli which utilized glycerol as a substrate have already reached a relatively high titer. Synthetic routes based on other intermediates like malonyl-CoA, beta-alanine and pyruvate have also been tested in model organisms like Escherichia coli, Saccharomyces cerevisiae. However, most of these processes were carried out under neutral pH conditions which would have an increased cost in fermentation broth neutralization and final product extraction in commercial scale production. In our recent work, 3-hydroxypropionate production was constructed based on lactate intermediate derived from glycolysis and fermentation followed by incorporation of the lactate utilization pathway from Megasphaera elsidenii. Protein engineering of CoA transferase was adapted to enable the transferring of CoA from 3-hydroxypropionic-CoA to lactate which facilitated the metabolic fluxing from lactate to 3-hydroxypropiniate. Also, adaptive evolution of Escherichia coli with minimal salt medium and glucose as sole carbon source was carried out to improve its productivity under low pH conditions.