Tuesday, July 31, 2007 - 2:30 PM
S117A

Enhanced propionic acid production from glycerol by metabolically engineered Propionibacterium acidipropionici

An Zhang and Shang-Tian Yang. The Department of Chemical and Biomolecular Engineering, The Ohio State University, 140W. 19th Ave. , Koffolt Laboratories, Columbus, OH 43210

With the increased production of biodiesels, large amounts of glycerol are produced as a byproduct with limited use, causing a significant environmental problem. It is thus desirable to use this waste glycerol as a renewable feedstock to produce industrial chemicals and fuels to replace fossil fuels and petrochemicals. In addition to its low cost and abundance, glycerol is also an attractive fermentation substrate because of its higher reduced level than those of sugars (sucrose, glucose, xylose, etc.) and other carbon sources such as lactate. In this work, glycerol as the carbon source in propionic acid fermentation by metabolically engineered Propionibacterium acidipropionici in a fibrous bed bioreactor (FBB) was studied. It was found that P. acidipropionici could use glycerol for its growth and produced propionic acid at a high yield of 0.71 g/g glycerol, which was much higher than that from glucose (0.55 g/g glucose). In addition, the production of acetic acid in glycerol fermentation was only 0.014 g/g glycerol, which was much less than that from glucose (0.1 g/g glucose).  Thus, glycerol fermentation produced a high purity propionic acid with the propionic acid to acetic acid ratio of ~50 (vs. ~5 from glucose fermentation), facilitating the recovery and purification of propionic acid from the fermentation broth by simple solvent extraction. The metabolic pathway shift and its effect on propionic and acetic acids production from different carbon sources can be attributed to cell’s needs to have NADH/NAD+ balance and maximum ATP production, as predicted by a stoichiometric metabolic model.

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