High-Cell Density Fermentation With An Acid-Tolerant Strain Of Propionibacterium Acidipropionici For Propionic Acid Production

Propionic acid is an important short-chain fatty acid with wide industrial applications. With the depletion of petroleum, rising oil price and market demanding, bio-based propionic acid has gained more and more attention. Propionibacterium acidpropioniciare Gram-positive, nonspore-forming, rod-shaped, anaerobic bacteria. It can be used to produce propionic acid with acetate, succinate and carbon dioxide as byproducts. To compete with petrochemical processes, a Propionibacterium acidipropionici acid-tolerant mutant strain was first developed by adaptation in a fibrous bed bioreactor (FBB) and serious sub-culturings on agar plates. Compared to the wild-type strain, the mutant strain gave higher productivity and product purity. Then a high-cell-density (HCD) fermentation process, with high propionic acid yield and productivity was developed.  A productivity of 2.89 g/L·h (vs. 0.5 g/L·h) was attained in repeated-batch HCD fermentation at pH 6.5. At lower pH values of 5.5 and 5.0, higher propionic acid yield and slightly lower productivity were obtained. The HCD fermentation process with the acid-tolerant strain can be used to produce propionic acid from glucose and other biomass feedstocks, which will be presented in this paper.