Carbon monoxide gasing leads to alcohol production and butyrate uptake without acetone formation in continuous cultures of Clostridium acetobutylicum

Abstract

Summary. When continuous, steady-state, glucose-limited cultures of Clostridium acetobutylicum were sparged with CO, the completely or almost completely acidogenic fermentations became solventogenic. Alcohol (butanol and ethanol) and lactate production at very high specific production rates were initiated and sustained without acetone, and little or no acetate and butyrate formation. In one fermentation, strong butyrate uptake without acetone formation was observed. Growth could be sustained even with 100% inhibition of H2 formation. Although CO gasing inhibited growth up to 50%, and H2 formation up to 100%, it enhanced the rate of glucose uptake up to 300%. The YATP was strongly affected and mostly reduced with respect to its steady-state value. The results support the hypothesis that solvent formation is triggered by an altered electron flow.

Biobutanol from Renewable Agricultural and Lignocellulose Resources and Its Perspectives as Alternative of Liquid Fuels

“…Although CO gasing inhibited growth up to 50%, and H 2 formation up to 100%, it enhanced the rate of glucose uptake up to 300%. These results support the hypothesis that solvent formation is triggered by an altered electron flow [77]. The metabolic modulation by CO was particularly effective when organic acids such as acetic and butyric acid were added to the fermentation as electron sinks.…”

Regulation of carbon and electron flow in Clostridium acetobutylicum grown in chemostat culture at neutral pH on mixtures of glucose and glycerol

“…1). Meyer et al (27) reported similar results when glucose-limited chemostat cultures of C. acetobutylicum were sparged with CO, a reversible inhibitor of hydrogenase activity. In such conditions, electrons produced by the glycolytic conversion of glucose to pyruvate and by the oxidation of pyruvate to acetyl-CoA were used to produce alcohols and lactate instead of hydrogen.…”

“…Two distinct conditions exist under which solvent formation may be initiated in continuous cultures of C. acetobutylicum: (i) low pH or addition of butyric acid results in the formation of butanol, ethanol, and acetone and is associated under steady-state conditions with a normal level of NADH and a high level of ATP (12,26); and (ii) decreasing the in vivo activity of the hydrogenase by carbon monoxide, methyl viologen, or iron limitation leads to alcohol production alone (16,27) and is correlated, under steady-state conditions, with high levels of both NADH and ATP (16,26). The shift observed when glycerol is metabolized at neutral pH belongs to this second category, as both high intracellular NADH and ATP concentrations and low hydrogen production were observed.…”

“…Lowering the intracellular pH and thereby increasing the concentration of undissociated butyric acid has a positive effect on the production of acetone and butanol (2,13,14,28,29,38). The alteration of the electron flow by carbon monoxide, a reversible inhibitor of the hydrogenase, can also induce the shift from an acidogenic fermentation to an alcohologenic one (9,20,25,27): alcohol (butanol and ethanol) and lactate production at very high specific rates is obtained, without acetone and little or no acetate and butyrate formation. The decrease of hydrogenase activity or concentration by iron limitation conditions (19) specifically yields butanol and ethanol as the major fermentation end products.…”

Regulation of Clostridium acetobutylicum metabolism as revealed by mixed-substrate steady-state continuous cultures: role of NADH/NAD ratio and ATP pool

“…High ATP concentration related to low ATP demand or high efficiency of ATP generation would lead to enhanced solvent production (i) for glucose-sufficient cultures at a low pH with biomass recycling (12,13); (ii) for iron-, nitrogen-, or phosphate-limited cultures (1,2,19); and (iii) during shifts induced on phosphatelimited cultures by lowering the pH or adding organic acids (6). Ethanol and butanol productions were associated with increased availability of reducing power (i) when the in vivo activity of the hydrogenase was decreased by CO gassing (5,10,13,14) or by adding methyl viologen (6); (ii) during a shift in solvent production induced by lowering the pH when acetyl coenzyme A (CoA) was first converted to acetone (a pathway consuming no reducing energy), creating a redox imbalance (6); (iii) when an NADH pressure was provided by culturing the microorganism on glucose and a more reduced substrate (21). Under such mixed substrate (glucose plus glycerol) growth, the culture was reported to be glucose but not glycerol limited.…”