title: Fermentation of xylose to succinate by enhancement of ATP supply in metabolically engineered Escherichia coli.
abstract: In Escherichia coli K12, succinate was not the dominant fermentation product from xylose. To reduce byproduct formation and increase succinate accumulation,pyruvate formate lyase and lactate dehydrogenase, encoded by pflB and ldhA genes, were inactivated. However, these mutations eliminated cell growth and xylose utilization. During anaerobic growth of bacteria, organic intermediates,such as pyruvate, serve as electron acceptors to maintain the overall redox balance. Under these conditions, the ATP needed for cell growth is derived from substrate level phosphorylation. In E. coli K12, conversion of xylose to pyruvate only yielded 0.67 net ATP per xylose during anaerobic fermentation. However, E. coli produces equimolar amounts of acetate and ethanol from two pyruvates, and these reactions generate one additional ATP. Conversion of xylose to acetate and ethanol increases the net ATP yield from 0.67 to 1.5 per xylose, which could meet the ATP needed for xylose metabolism. A pflB deletion strain cannot convert pyruvate to acetyl coenzyme A, the precursor for acetate and ethanol production, and could not produce the additional ATP. Thus,the double mutations eliminated cell growth and xylose utilization. To supply the sufficient ATPs, overexpression of ATP-forming phosphoenolpyruvate-carboxykinase from Bacillus subtilis 168 in an ldhA, pflB, and ppc deletion strain resulted in a significant increase in cell mass and succinate production. In addition, fermentation of corn stalk hydrolysate containing a high percentage of xylose and glucose produced a final succinate concentration of 11.13 g l−1 with a yield of1.02 g g−1 total sugars during anaerobic fermentation.
authors.affiliation: State Key Laboratory of Materials-Oriented Chemical Engineering, College of Biotechnology and Pharmaceutical Engineering, Nanjing University of Technology, Nanjing, China.
authors.forename: Rongming
authors.initials: R
authors.lastname: Liu
authors.forename: Liya
authors.initials: L
authors.lastname: Liang
authors.forename: Kequan
authors.initials: K
authors.lastname: Chen
authors.forename: Jiangfeng
authors.initials: J
authors.lastname: Ma
authors.forename: Min
authors.initials: M
authors.lastname: Jiang
authors.forename: Ping
authors.initials: P
authors.lastname: Wei
authors.forename: Pingkai
authors.initials: P
authors.lastname: Ouyang
mesh_terms: D000255:Adenosine Triphosphate / Q000096:biosynthesis*; D001412:Bacillus subtilis / Q000201:enzymology / Q000235:genetics; D018533:Biomass; D001711:Biotransformation; D003001:Cloning, Molecular; D048168:Escherichia coli K12 / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism*; D005285:Fermentation; D017353:Gene Deletion; D015870:Gene Expression; D060847:Metabolic Engineering; D053858:Metabolic Networks and Pathways / Q000235:genetics*; D019764:Phosphoenolpyruvate Carboxykinase (ATP) / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D019802:Succinic Acid / Q000378:metabolism*; D014994:Xylose / Q000378:metabolism*; D003313:Zea mays
chemical_list: D011994:Recombinant Proteins; D000255:Adenosine Triphosphate; D014994:Xylose; D019802:Succinic Acid; D019764:Phosphoenolpyruvate Carboxykinase (ATP)