Production of butyric acid at constant pH by a solventogenic strain of Clostridium beijerinckii

A solventogenic strain of Clostridium beijerinckii, NRRL B-598, was cultured for the production of butyric acid as the main fermentation product. However, unlike typical acetone-butanol-ethanol (ABE) fermentations, where pH is not regulated, in this study the pH was kept constant during fermentation. From the five pH values tested, 6.0, 6.5, 7.0, 7.5 and 8.0, pH 6.5 and 7.0 resulted in the highest concentrations of butyric acid, at 9.69 ± 0.09 g L–1 and 11.5 ± 0.39 g L–1, respectively. However, a low concentration of solvents, 1.8 ± 0.22 g L–1, was only reached at pH 7.0. These results are comparable with those from typical butyric acid producers, i.e. Clostridium butyricum and Clostridium tyrobutyricum strains. At pH 7.0, we succeeded in suppressing sporulation and prolonging the population viability, which was confirmed by flow cytometry combined with double fluorescence staining.