Investigation of the key factors on 3-hydroxypropionic acid production with different recombinant strains.

3-Hydroxypropionic acid (3-HP) is an important compound and precursor for a series of chemicals and polymeric materials. In this study, the 3-HP producing bacteria were constructed and studied for efficient synthesis of 3-HP. The results indicated that the instability of glycerol dehydratase (GDHt) affected the 3-HP production significantly, which was successfully solved by the expression of glycerol dehydratase reactivase (GdrB), with fivefold increase in 3-HP yield. Meanwhile, NAD+-regenerating enzymes GPD1 (glycerol-3-phosphate dehydrogenase) was expressed; however, the results showed 3-HP was significantly decreased from 56.73-4 mM, and malic acid was obviously increased. Analysis of the C flux distribution showed that the main reason for the results was the lack of NAD+. The addition of NAD+ further increased the 3-HP production to 23.87 mM, demonstrating that the "regeneration of NAD+" was the major factor for enhancing 3-HP production.