(585m) Construction and Characterization Of Ack and Pta Gene-Deleted Mutants Of Propionibacterium Freudenreichii For Enhanced Propionic Acid Fermentation

Propionic acid is a widely used industrial product currently produced mainly via petrochemical processes. As the crude oil price has surpassed US$100 per barrel, there have been increasing interests in propionic acid production from renewable bioresources by fermentation using propionibacteria. The main metabolic product of Propionibacterium freudenreichii subsp. shermanii is propionic acid with acetic and succinic acids as two by-products. Propionic and succinic acids are generated in the dicarboxylic acid pathway, in which the formation of both acids is directly correlated with each other. On the other hand, acetic acid is formed in a separate pathway, first from pyruvate decarboxylation to acetyl-CoA and then to acetyl phosphate and finally to acetic acid. The last two steps of acetic acid formation are catalyzed by phosphotransacetylase (PTA) and acetate kinase (ACK), respectively. In order to enhance propionic acid production, pta and/or ack were mutated through homologous recombination. Gene mutations were confirmed by PCR. Fermentations in serum bottles and fermentors using different carbon sources were conducted for mutants and wild type. Fermentation results showed differences regarding acetic and propionic acids formation between the wild type and single knock-out mutants. The effects of these gene knockouts on the flux distributions between acetic acid and propionic acid biosynthesis pathways were investigated and will be presented in this paper.