Effects of over-expression of glycerol dehydrogenase and 1,3-propanediol oxidoreductase on bioconversion of glycerol into 1,3-propandediol by <Emphasis Type="Italic">Klebsiella pneumoniae</Emphasis> under micro-aerobic conditions

Glycerol dehydrogenase (GDH) and 1,3-propanediol (1,3-PD) oxidoreductase had been proved two key enzymes for 1,3-PD production by Klebsiella pneumoniae. Fed-batch fermentations of the recombinant K. pneumoniae strains, over-expressing the two enzymes individually, were carried out under micro-aerobic conditions, and the behaviors of the recombinants were investigated. Results showed that over-expression of 1,3-PD oxidoreductase did not affect the concentration of 1,3-PD. However, it enhanced the molar yield from 50.6 to 64.0% and reduced the concentration of by-products. Among them, the concentrations of lactic acid, ethanol and succinic acid were decreased by 51.8, 50.6 and 47.4%, respectively. Moreover, in the recombinant the maximal concentration of 3-hydroxypropionaldehyde decreased by 73.6%. Over-expression of GDH decreased the yield of ethanol and 2,3-butanediol, meanwhile it increased the concentration of acetic acid. No significant changes were observed both in 1,3-PD yield and glycerol flux distributed to oxidative branch.