title: Metabolic engineering of Propionibacterium freudenreichii: effect of expressing phosphoenolpyruvate carboxylase on propionic acid production.
abstract: Propionic acid is currently produced mainly via petrochemicals, but there is increasing interest in its fermentative production from renewable biomass. However, the current propionic acid fermentation process suffers from low product yield and productivity. In this work, the gene encoding phosphoenolpyruvate carboxylase (PPC) was cloned from Escherichia coli and expressed in Propionibacterium freudenreichii. PPC catalyzes the conversion of phosphoenolpyruvate to oxaloacetate with the fixation of one CO2. Its expression in P. freudenreichii showed profound effects on propionic acid fermentation. Compared to the wild type, the mutant expressing the ppc gene grew significantly faster, consumed more glycerol, and produced propionate to a higher final titer at a faster rate. The mutant also produced significantly more propionate from glucose under elevated CO2 partial pressure. These effects could be attributed to increased CO2 fixation and resulting changes in the flux distributions in the dicarboxylic acid pathway.
authors.affiliation: William G. Lowrie Department of Chemical and Biomolecular Engineering, The Ohio State University, 140 West 19th Avenue, Columbus, OH, 43210, USA.
authors.forename: Ehab Mohamed
authors.initials: EM
authors.lastname: Ammar
authors.forename: Ying
authors.initials: Y
authors.lastname: Jin
authors.forename: Zhongqiang
authors.initials: Z
authors.lastname: Wang
authors.forename: Shang-Tian
authors.initials: ST
authors.lastname: Yang
mesh_terms: D005990:Glycerol / Q000378:metabolism; D060847:Metabolic Engineering; D010730:Phosphoenolpyruvate Carboxylase / Q000378:metabolism*; D011422:Propionates / Q000378:metabolism*; D011424:Propionibacterium / Q000201:enzymology / Q000378:metabolism*
chemical_list: D011422:Propionates; D010730:Phosphoenolpyruvate Carboxylase; C029658:propionic acid; D005990:Glycerol