Process Engineering of Clostridium Tyrobutyricum to Improve Butyric Acid Production

Butyric acid production by Clostridium tyrobutyricum has drawn increasing attention because it is widely used in food and pharmaceutical industries. Clostridium tyrobutyricum mutant PAK-Em with inactivated ack gene, encoding acetate kinase, was used in fermentations to produce butyric acid from glucose. A fibrous-bed bioreactor (FBB) was used to immobilize and adapt PAK-Em cells, which boosted the butyric acid yield to 0.38 g/g at pH 5.5 and 0.42 g/g at pH 6.5.  PAK-EM produced much more butyric acid (23.2 g/L vs. 17.2 g/L at pH 5.5 and 63.0 g/L vs. 15.7 g/L at pH 6.5) than the wild type, but had a lower specific growth rate (0.08 h^-1 vs. 0.11 h^-1 at pH 5.5 and 0.09h^-1 vs. 0.10 h^-1 at pH 6.5) in the FBB. The integration of metabolic engineering and process parameter optimization increased butyric acid production significantly.