A comparison of three pH control methods for revealing effects of undissociated butyric acid on specific butanol production rate in batch fermentation of Clostridium acetobutylicum

Abstract

pH control has been essential for butanol production with Clostridium acetobutylicum. However, it is not very clear at what pH level the acid crash will occur, at what pH level butanol production will be dominant, and at what pH level butyric acid production will be prevailing. Furthermore, contradictory results have been reported about required acidic conditions for initiation of solventogenesis. In this study, with the aim of further understanding the role of undissociated butyric acid in butanol production, we investigated the correlation between undissociated butyric acid concentration and specific butanol production rate in batch fermentation of Clostridium acetobutylicum by comparing three pH control approaches: NaOH neutralization (at 12, 24 or 36 h), CaCO3 supplementation (2, 5, or 8 g/l) and NaOAc buffering (pH 4.6, 5.0 or 5.6). By neutralizing the fermentation pH to ~5.0 at different time, we observed that neutralization should take place at the beginning of exponential phase (12 h), and otherwise resulting in lower concentrations of undissociated butyric acid, cell biomass and final butanol. CaCO3 supplementation extended cell growth to 36 h and resulted in higher butyrate yield under 8 g/L of CaCO3. In the NaOAc buffering, the highest specific butanol rate (0.58 h−1) was associated with the highest undissociated butyric acid (1.92 g/L). The linear correlation of the undissociated butyric acid with the specific butanol production rates suggested the undissociated butyric acid could be the major driving force for butanol production.

Impact of glucose concentration on productivity and yield of hydrogen production by the new isolate Clostridium beijerinckii Br21

“…H 2 accumulation in the batch reactors might also have inhibited fermentation and lowered the H 2 yields . However, as mentioned before, the same inverse effect for substrate concentration versus H 2 yield has been verified during the operation of continuous reactors, which do not accumulate H 2 inside the device …”

“…In other words, higher glucose concentration could increase H 2 production; however, excessive substrate concentration could decrease such production . Higher conversion ratios (Y H2/S and Y X/S ) were achieved at low initial glucose concentration, indicating that glucose was more efficiently employed for cell growth and H 2 production in this condition because H 2 was produced in the Clostridium exponential growth phase.…”

Genomic, Transcriptional, and Phenotypic Analysis of the Glucose Derepressed Clostridium beijerinckii Mutant Exhibiting Acid Crash Phenotype

“…The acid toxicity causing the acid crash phenotype can be relieved by increasing the culture pH, thereby resulting in decreasing the concentration of undissociated acids that are toxic to the cell . Therefore, we further investigated the fermentation phenotype of BA105 mutant in pH‐controlled batch fermentations.…”

Fermentation of oxidized hexose derivatives by Clostridium acetobutylicum

“…Research on C. acetobutylicum has historically been centered on strategies for increasing butanol yield through genetic engineering and manipulation of fermentation conditions [54]. More recent publications have emerged in the literature describing the production of other commercially viable products, such as isopropanol and 2,3 butanediol from C. acetobutylicum [55,56].…”