Abstract
For every 9 kg of biodiesel produced, about 1 kg of crude glycerol is left behind which poses a challenge and opportunity to find the best uses of the waste. Here we present our results aimed at the production of a valuable platform chemical, 3-hydroxypropionic acid (3-HP), from glycerol using genetically engineered Escherichia coli and Klebsiella pneumoniae strains. In one approach, we screened and expressed various aldehyde dehydrogenases (ALDHs) along with glycerol dehydratase (GDHt) in E. coli and demonstrated that a recombinant bearing GDHt and an ALDH produced 3-HP at 38 g/L in 72 h with an average yield of 33% on glycerol. To improve the yield, the recombinant E. coli strain was further developed by disrupting the gene glpF which encodes glycerol kinase, the first enzyme of glycerol respiratory pathway. The resting cells of the recombinant mutant produced 3-HP at 33 g/L in 48 h with an average yield of 80 % on glycerol. In the other approach, when an NAD+-dependent ALDH (PuuC) of K. pneumoniae DSM 2026 which oxidizes 3-hydroxypropionaldehyde to 3-HP was homologously overexpressed in K. pneumoniae DdhaT mutant, the strain co-produced 16.0 g 3-HP and 16.8 g 1,3-propanediol (1,3-PDO) per liter in 24 h with a cumulative yield of 51% on glycerol. This talk will review our recent work on the metabolic pathway engineering for redox balance and diverting carbon flux for the production of 3-HP and 1,3-PDO from glycerol at significant scales.