Improvement of the long-term survival of Acetobacterium woodii by limiting acetate production

Summary The viable count in fructose-grown cultures of Acetobacterium woodii fell to undetectable levels 186 h after the stationary phase was reached. The loss of viability was due to accumulation of undissociated acetic acid, since loss of viability could be induced artificially in cultures grown at pH 6.8 by adjusting the pH to 5.0 or by adding high concentrations of acetate. Survival was greatly improved when cultures were grown at low initial fructose concentrations ( 2 g/l) to limit acetate production, since viable cells could still be detected after 73d.     

Bioconversion of Butyric Acid to Butanol by Clostridium saccharoperbutylacetonicum N1-4 (ATCC 13564) in a Limited Nutrient Medium

This study was designed to investigate the ability of Clostridium saccharoperbutylacetonicum N1-4 to produce butanol in a limited nutrient medium using mixtures of glucose and butyric acid as substrates. Specific combinations of glucose and butyric acid were found to influence the enhancement and retardation of butanol production as well as the reduction and modulation of the number of bacterial cells. Increasing the butyric acid concentration leads to the inhibition of bacterial growth, whereas the presence of (0?C5?g/L) butyric acid and (0?C10?g/L) glucose enhances the butanol production. The combination of 5?g/L butyric acid with 5 and 10?g/L of glucose was found to be the most suitable, but the use of glucose at concentrations greater than 10?g/L shifted the optimal butyric acid concentrations to 10 and 15?g/L for maximum butanol production signifying the requirement of a specific combination of glucose and butyric acid for enhanced butanol production in the fermentation process. C. saccharoperbutylacetonicum N1-4 demonstrated the ability to produce butanol in the absence of glucose, but no acetone or ethanol was produced under these conditions, reflecting the nature of the pathways involved in the production of butanol using only butyric acid. Ten grams per litre of butyric acid was found able to produce 13?g/L of butanol in the presence of 20?g/L of glucose, and 0.7?g/L butanol was produced in the absence of glucose. This study indicates the importance of the glucose to butyric acid ratio to the enhancement of butanol production.     

Direct fermentation of gelatinized sago starch to acetone–butanol–ethanol by Clostridium acetobutylicum

Direct fermentation of gelatinized sago starch into solvent (acetone–butanol–ethanol) by Clostridium acetobutylicum P262 was studied using a 250 ml Schott bottle anaerobic fermentation system. Total solvent production from fermentation using 30 g sago starch/l (11.03g/l) was comparable to fermentation using corn starch and about 2-fold higher than fermentation using potato or tapioca starch. At the range of sago starch concentration investigated (10–80 g/l), the highest total solvent production (18.82 g/l) was obtained at 50 g/l. The use of a mixture of organic and inorganic nitrogen source (yeast extract + NH₄NO₃) enhanced growth of C. acetobutylicum, starch hydrolysis and solvent production (24.47 g/l) compared to the use of yeast extract alone. This gave the yield based on sugar consumed of 0.45 g/g. Result from this study also showed that the individual concentrations of nitrogen and carbon influenced solvent production to a greater extent than did carbon to nitrogen (C/N) ratio.     

Impact of pH and butyric acid on butanol production during batch fermentation using a new local isolate of Clostridium acetobutylicum YM1

The effect of pH and butyric acid supplementation on the production of butanol by a new local isolate of Clostridium acetobutylicum YM1 during batch culture fermentation was investigated. The results showed that pH had a significant effect on bacterial growth and butanol yield and productivity. The optimal initial pH that maximized butanol production was pH 6.0 ± 0.2. Controlled pH was found to be unsuitable for butanol production in strain YM1, while the uncontrolled pH condition with an initial pH of 6.0 ± 0.2 was suitable for bacterial growth, butanol yield and productivity. The maximum butanol concentration of 13.5 ± 1.42 g/L was obtained from cultures grown under the uncontrolled pH condition, resulting in a butanol yield (Y_P/S) and productivity of 0.27 g/g and 0.188 g/L h, respectively. Supplementation of the pH-controlled cultures with 4.0 g/L butyric acid did not improve butanol production; however, supplementation of the uncontrolled pH cultures resulted in high butanol concentrations, yield and productivity (16.50 ± 0.8 g/L, 0.345 g/g and 0.163 g/L h, respectively). pH influenced the activity of NADH-dependent butanol dehydrogenase, with the highest activity obtained under the uncontrolled pH condition. This study revealed that pH is a very important factor in butanol fermentation by C. acetobutylicum YM1.     

Enhanced butanol production by optimization of medium parameters using Clostridium acetobutylicum YM1

A new isolate of the solvent-producing Clostridium acetobutylicum YM1 was used to produce butanol in batch culture fermentation. The effects of glucose concentration, butyric acid addition and C/N ratio were studied conventionally (one-factor-at-a-time). Moreover, the interactions between glucose concentration, butyric acid addition and C/N ratio were further investigated to optimize butanol production using response surface methodology (RSM). A central composite design was applied, and a polynomial regression model with a quadratic term was used to analyze the experimental data using analysis of variance (ANOVA). ANOVA revealed that the model was highly significant (p < 0.0001) and the effects of the glucose and butyric acid concentrations on butanol production were significant. The model validation experiment showed 13.82 g/L butanol was produced under optimum conditions. Scale up fermentation in optimized medium resulted in 17 g/L of butanol and 21.71 g/L of ABE. The experimental data of scale up in 5 L bioreactor and flask scale were fitted to kinetic mathematical models published in the literature to estimate the kinetic parameters of the fermentation. The models used gave the best fit for butanol production, biomass and glucose consumption for both flask scale and bioreactor scale up.     

Biobutanol production from rice bran and de-oiled rice bran by <Emphasis Type="Italic">Clostridium saccharoperbutylacetonicum</Emphasis> N1-4

Rice bran (RB) and de-oiled rice bran (DRB) have been treated and used as the carbon source in acetone–butanol–ethanol (ABE) production using Clostridium saccharoperbutylacetonicum N1-4. The results showed that pretreated DRB produced more ABE than pretreated RB. Dilute sulfuric acid was the most suitable treatment method among the various pretreatment methods that were applied. The highest ABE obtained was 12.13 g/L, including 7.72 g/L of biobutanol, from sulfuric acid. The enzymatic hydrolysate of DRB (ESADRB), when treated with XAD-4 resin, resulted in an ABE productivity and yield of 0.1 g/L h and 0.44 g/g, respectively. The results also showed that the choice of pretreatment method for RB and DRB is an important factor in butanol production.