title: The effect of carbon sources and lactate dehydrogenase deletion on 1,2-propanediol production in Escherichia coli.
abstract: In previous studies, we showed that cofactor manipulations can potentially be used as a tool in metabolic engineering. In this study, sugars similar to glucose, that can feed into glycolysis and pyruvate production, but with different oxidation states, were used as substrates. This provided a simple way of testing the effect of manipulating the NADH/NAD+ ratio or the availability of NADH on the metabolic patterns of Escherichia coli under anaerobic conditions and on the production of 1,2-propanediol (1,2-PD), which requires NADH for its synthesis. Production of 1,2-PD was achieved by overexpressing the two enzymes methylglyoxal synthase from Clostridium acetobutylicum and glycerol dehydrogenase from E. coli. In addition, the effect of eliminating a pathway competing for NADH by using a ldh(-) strain (without lactate dehydrogenase activity) on the production of 1,2-PD was investigated. The oxidation state of the carbon source significantly affected the yield of metabolites, such as ethanol, acetate and lactate. However, feeding a more reduced carbon source did not increase the yield of 1,2-PD. The production of 1,2-PD with glucose as the carbon source was improved by the incorporation of a ldh(-) mutation. The results of these experiments indicate that our current 1,2-PD production system is not limited by NADH, but rather by the pathways following the formation of methylglyoxal.
authors.affiliation: Departments of Bioengineering and Chemical Engineering, Rice University, Houston, Texas, USA.
authors.forename: Susana J
authors.initials: SJ
authors.lastname: Berríos-Rivera
authors.forename: Ka-Yiu
authors.initials: KY
authors.lastname: San
authors.forename: George N
authors.initials: GN
authors.lastname: Bennett
mesh_terms: D002244:Carbon / Q000378:metabolism*; D003470:Culture Media; D004926:Escherichia coli / Q000201:enzymology* / Q000235:genetics; D017353:Gene Deletion; D005942:Gluconates / Q000378:metabolism; D005947:Glucose / Q000378:metabolism; D007770:L-Lactate Dehydrogenase / Q000235:genetics* / Q000378:metabolism; D009243:NAD / Q000378:metabolism; D010084:Oxidation-Reduction; D010957:Plasmids; D019946:Propylene Glycol / Q000378:metabolism*; D013012:Sorbitol / Q000378:metabolism
chemical_list: D003470:Culture Media; D005942:Gluconates; D009243:NAD; D013012:Sorbitol; D019946:Propylene Glycol; D002244:Carbon; D007770:L-Lactate Dehydrogenase; D005947:Glucose; C030691:gluconic acid