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This study compared free and immobilized cells with palm oil and hexanol as an extractant in a large volume ratio of extractant to the broth. Fermentation was conducted using TYA (Tryptone-Yeast-Acetate) media, glucose as the substrate and the palm oil, hexanol, and a mixture of hexanol and palm oil with a composition of 1:1 v/v as an extractant in the fermentation with a large volume ratio of extractant to broth of 5. The strain was inoculated as free-suspended cells of C. saccharoperbutylacetonicum N1-4 and immobilized cells in calcium alginate. The best extractant results for the acetone fermentation process in the ratio of extractive fermentation of free cells and immobilized cells were using palm oil as extractants. This extractant harvested acetone well, with the acetone concentration in the extractant at 18.41 g/L in free cell fermentation and 17.07 g/L in immobilized cell fermentation. The maximum total acetone concentration was up to 93.72 g/L broth. Using palm oil as an extractant in a large extractant volume combined with immobilization is an alternative to enhance bioacetone production by effectively reducing the toxicity effect of the products and minimizing nutrient requirements.

This study compared free and immobilized cells with palm oil and hexanol as an extractant in a large volume ratio of extractant to the broth. Fermentation was conducted using TYA (Tryptone-Yeast-Acetate) media, glucose as the substrate and the palm oil, hexanol, and a mixture of hexanol and palm oil with a composition of 1:1 v/v as an extractant in the fermentation with a large volume ratio of extractant to broth of 5. The strain was inoculated as free-suspended cells of C. saccharoperbutylacetonicum N1-4 and immobilized cells in calcium alginate. The best extractant results for the acetone fermentation process in the ratio of extractive fermentation of free cells and immobilized cells were using palm oil as extractants. This extractant harvested acetone well, with the acetone concentration in the extractant at 18.41 g/L in free cell fermentation and 17.07 g/L in immobilized cell fermentation. The maximum total acetone concentration was up to 93.72 g/L broth. Using palm oil as an extractant in a large extractant volume combined with immobilization is an alternative to enhance bioacetone production by effectively reducing the toxicity effect of the products and minimizing nutrient requirements. [ABSTRACT FROM AUTHOR]

Repeated-batch fermentation experiments were carried out to determine the best switching time, stability, and consistency of the process for enhanced biohydrogen production from Rice-bran. After the initial batch process, one repeated Cycle was made for three ‘runs’ to determine the best switching time, the ‘runs’ were terminated after 45 h, 60 h and 75 h, respectively. The effect of switching time on cell growth, hydrogen yield and productivity was investigated. The pattern of cell growth suggested that switching from batch mode to repeated batch mode at the 60th h led to the production of the highest amount of hydrogen. The lowest pH value (5.22) was observed at the end of the first fermentation Cycle. Cycle 2 has the highest amount of cumulative hydrogen production (mL 1280.3 L-1 medium) and the highest pH value (5.38). The profiles of the biomass concentration for all the Cycles were similar showing the stability and consistency of the process. There was an increment of 22 % in the overall Hydrogen gas production rate for the repeated batch process when compared to that of the ordinary batch process this result justified the use of the repeated batch system as a process that enhances biohydrogen production.

Highlights • sol operon overexpression enhanced acid re-assimilation and ABE level (by 20%). • Further overexpression of cassette EC improved both butanol and ABE production. • Mutants can efficiently convert acetate-pretreated biomass to ABE with high yield. Abstract In the clostridial acetone-butanol-ethanol (ABE) fermentation, the intermediate acetate and butyrate are re-assimilated for solvent production. Here, key genes in ABE pathways in Clostridium saccharoperbutylacetonicum N1-4 were overexpressed to enhance acid re-assimilation and solvent production. With the overexpression of sol operon, acid re-assimilation was enhanced, and ABE production was increased by 20%, with ethanol production increased by six times but almost no increase in butanol production. To further drive carbon flux for C4 metabolites and ultimate butanol production, key genes including hbd, thl, crt and bcd in butanol production pathway were further overexpressed. Compared to the control, butanol, acetone and total ABE production in the new strain was increased by 8%, 18%, and 12.4%, respectively. Finally, simultaneous saccharification and fermentation was carried out using acetate-pretreated switchgrass. 15.4 g/L total ABE (with a yield of 0.31 g/g) was produced in both engineered strains, which was significantly higher than the control. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • An innovative acetic-acid-based biomass pretreatment method was developed. • Both the prehydrolysates and the solid cellulosic fraction were highly fermentable. • 8.6 g/L butanol was obtained from simultaneous saccharification and fermentation. • Comprehensive carbon utilization was realized with a tailored pretreatment strategy. Abstract For bioenergy production from lignocellulosic biomass, most biomass pretreatment processes need to use some chemical reagent as the catalyst to overcome the biomass recalcitrance barrier. Such reagents are usually severe inhibitors for the subsequent microbial fermentation process. Therefore, in many cases, the liquid prehydrolysates fraction (LPF) is discarded after the pretreatment, which is a tremendous waste of materials and leads to additional pollution. Biobutanol produced from the acetone, butanol and ethanol (ABE) fermentation process has been of great interests recently due to its high value as a bioenergy source or biochemical. During ABE fermentation, acetic acid (AA) is produced and then re-assimilated as a carbon source. Thus, AA is a substrate rather than an inhibitor for biobutanol production. In this study, we employed AA as the chemical catalyst for the pretreatment of switchgrass which then be used for ABE production through simultaneous saccharification and fermentation (SSF) with hyper-butanol producing Clostridium saccharoperbutylacetonicum N1-4. Through systematic investigation of the pretreatment conditions and fermentation, we concluded that the optimized condition for switchgrass pretreatment was with 3 g/L AA at 170 °C for 20 min. Both LPF and solid cellulosic fraction (SCF) of the pretreated biomass were highly fermentable. In the fermentation with the SCF/LPF mixture as the substrate, 8.6 g/L butanol (corresponding to a yield of 0.16 g/g) was obtained. Overall, here we demonstrated an innovative and tailored biomass pretreatment strategy for comprehensive and efficient carbon source utilization for bioenergy production. [ABSTRACT FROM AUTHOR]

Palm kernel cake (PKC), a by-product of palm oil industry, contains glucose and mannose as hexose sugars. This study was performed to determine the feasibility of using PKC as a lignocellulosic substrate for biobutanol production by Clostridium saccharoperbutylacetonicum N1-4 in an acetone-butanol-ethanol (ABE) fermentation process. Moreover, the effect of tryptone-yeast extract-acetate (TYA) medium and P2 medium on biobutanol production was evaluated. Experimental results showed that butanol production of 3.05 g/L was obtained using mannose sugar, which was comparable to 3.61 g/L butanol production measured using glucose. Moreover, the maximum production of biobutanol (0.38 g/L) was obtained at a PKC concentration of 30%, indicating the possibility of PKC utilization in butanol production. ABE fermentation of PKC using distilled water, TYA medium, and P2 medium showed that the highest butanol production (0.26 g/L) with ABE production of 0.38 g/L was obtained when ABE fermentation was conducted in P2 medium.

Clostridium saccharoperbutylacetonicum N1-4 has great potentials for acetone-butanol-ethanol (ABE) production from lignocellulosic carbon sources. However, fundamental information about its metabolism of lignocellulosic sugars and tolerance to fermentation inhibitors is not available. Here, we systematically evaluated effects of representative sugars and lignocellulosic inhibitors on ABE fermentation by C. saccharoperbutylacetonicum . Results indicated that C. saccharoperbutylacetonicum can use glucose, cellobiose, xylose, arabinose and mannose efficiently, while degrade galactose slowly and incompletely. Glucose was the most preferable carbon source that has shown carbon catabolite repression (CCR) on the degradation of other sugars. However, the actual sugar preference is highly dependent on the composition (including sugar types and concentrations). Ferulic acid, syringaldehyde and ρ-coumaric acid are potent phenolic inhibitors, with ρ-coumaric acid as the most toxic. C. saccharoperbutylacetonicum can tolerate up to 0.8, 0.8 and 0.4 g/L of ferulic acid, syringaldehyde and ρ-coumaric acid, respectively. Furfural and hydroxymethylfurfural (HMF) are inhibitory but not as toxic as phenolic inhibitors. C. saccharoperbutylacetonicum can tolerate up to 3 g/L furfural or HMF individually or as a mixture (1.5 g/L for each). Both furfural and HMF can be completely converted into their corresponding alcohols, with furfural is more rapidly transformed than HMF. Comparing to other prominent solventogenic clostridia, C. saccharoperbutylacetonicum can tolerate higher or at least comparable levels of inhibitors; it can adapt to inhibition conditions and produce more ABE than the control. Therefore, our results testified that C. saccharoperbutylacetonicum is a robust workhorse for biofuel production. [ABSTRACT FROM AUTHOR]

In this work, hydrolysis of cellulose and hemicellulose content of palm kernel cake (PKC) by different types of hydrolytic enzymes was studied to evaluate monomeric sugars released for production of biobutanol by Clostridium saccharoperbutylacetonicum N1-4 (ATCC 13564) in acetone–butanol–ethanol (ABE) fermentation. Experimental results revealed that when PKC was hydrolyzed by mixed β-glucosidase, cellulase and mannanase, a total simple sugars of 87.81 ± 4.78 g/L were produced, which resulted in 3.75 ± 0.18 g/L butanol and 6.44 ± 0.43 g/L ABE at 168 h fermentation. In order to increase saccharolytic efficiency of enzymatic treatment, PKC was pretreated by liquid hot water before performing enzymatic hydrolysis. Test results showed that total reducing sugars were enhanced to 97.81 ± 1.29 g/L with elevated production of butanol and ABE up to 4.15 ± 1.18 and 7.12 ± 2.06 g/L, respectively which represented an A:B:E ratio of 7:11:1. [ABSTRACT FROM AUTHOR]

Palm oil mill effluent (POME), an abundant and low-cost agro-industrial residue, was utilized for the production of butanol in the anaerobic process of acetone–butanol–ethanol (ABE) fermentation. The ABE process was performed by the cultivation of Clostridium saccharoperbutylacetonicum N1-4 (ATCC 13564) in raw POME medium without supplementation. The effect of various process parameters, including pH, incubation temperature, agitation and inoculums size on butanol production, was studied. Experimental results showed that the highest butanol levels could be produced when the initial pH of culture medium, incubation temperature, agitation speed and inoculums size were set at 5.8, 30 °C, 100 rpm and 15% (v/v), respectively. Results revealed that the existence of crude palm oil (CPO) in the POME composition had an adverse effect on butanol synthesis by Clostridial cells. The highest butanol and ABE concentrations of 0.9 g/L and 2.09 g/L were produced, respectively, when operating variables tested were set at their optimum levels under the absence of CPO. [ABSTRACT FROM AUTHOR]

In the effort of developing bioenergy source materials, a laboratorium study was performed to investigate the effects of substrate types and concentrations on the production of acetone-butanol-ethanol (ABE) from various substrates by Clostridium saccharoperbutylacetonicum N1-4 (ATCC 13564) in defined TYA (Tryptone-Yeast extract-Acetate) media. The results demonstrated that the ABE ratios produced by the strain N1-4 were greatly influenced by the types of substrate and the concentrations being used. It was also shown that fermentation of disaccharides (cellobiose and dextrin) by the strain N1-4 could give relatively as high butanol and ABE yields as glucose fermentation after 24 h fermentation time. The strain N1-4 was also found to be able to ferment xylans from birchwood sources producing a relatively high ABE concentration, especially at a prolonged incubation time (after 48 h incubation period). A subsequent experiment using several different concentrations of glucose or cellobiose revealed that the higher the concentration of the substrate being used, then the higher the total ABE concentration or productivity could be obtained but not necessarily in the same increasing ratio. To the best of our knowledge, there was no other previous study about the effect of substrate type and concentration on the ABE ratio by C. saccharoperbutylacetonicum N1-4 (ATCC 13564) using various substrates in defined TYA media, specifically by using xylans and dextrin substrates.

The economic feasibility of acetone–butanol–ethanol (ABE) fermentation is greatly affected by the type of raw material used. The easy availability of eucalyptus from marginal environments is an alternative feedstock for use as raw material to reduce the production cost. In this study, hydrolyzed eucalyptus was used for ABE production without any nutrients supplementation. Increasing the solid concentration in the eucalyptus slurry from 6.7% ( w -dry matter/ v ) to 25% led to an increase in the initial glucose concentration from 33.7 g/L to 86.7 g/L after enzymatic hydrolysis. Dosed cellulases not only hydrolyzed cellulose but also supplied nitrogen source for ABE producing strain. However, ABE production from the obtained hydrolysate decreased when the solid concentration was increased to more than 10%. The maximum ABE of 12.3 g/L was obtained at 10% solid concentration, with an initial glucose concentration of approximately 40 g/L. In addition, the fermentation capability of eucalyptus hydrolysate was found to be improved by diluting the hydrolysate, which prevented inhibition by substrate and fermentation inhibitors. Finally, ABE concentration was improved to 13.1 g/L by diluting the hydrolysate from the initial solid concentration of 25% to an initial glucose concentration of 45 g/L, which resulted in ABE productivity of 0.109 g/L/h and ABE yield of 0.413 g/g. Thus, the high ABE production from eucalyptus makes it a potential feedstock for biofuel production. [ABSTRACT FROM AUTHOR]

Palm kernel cake (PKC) was used for biobutanol production by Clostridium saccharoperbutylacetonicum N1-4 in acetone–butanol–ethanol (ABE) fermentation. PKC was subjected to acid hydrolysis pretreatment and hydrolysates released were detoxified by XAD-4 resin. The effect of pH, temperature and inoculum size on butanol production was evaluated using an empirical model. Twenty ABE fermentations were run according to an experimental design. Experimental results revealed that XAD-4 resin removed 50% furfural and 77.42% hydroxymethyl furfural. The analysis of the empirical model showed that linear effect of inoculums size with quadratic effect of pH and inoculum size influenced butanol production at 99% probability level ( P < 0.01). The optimum conditions for butanol production were pH 6.28, temperature of 28 °C and inoculum size of 15.9%. ABE fermentation was carried out under optimum conditions which 0.1 g/L butanol was obtained. Butanol production was enhanced by diluting PKC hydrolysate up to 70% in which 3.59 g/L butanol was produced. [ABSTRACT FROM AUTHOR]

Palm kernel cake (PKC), a by-product of palm oil industry, contains glucose and mannose as hexose sugars. This study was performed to determine the feasibility of using PKC as a lignocellulosic substrate for biobutanol production by Clostridium saccharoperbutylacetonicum N1-4 in an acetone-butanol-ethanol (ABE) fermentation process. Moreover, the effect of tryptone-yeast extract-acetate (TYA) medium and P2 medium on biobutanol production was evaluated. Experimental results showed that butanol production of 3.05 g/L was obtained using mannose sugar, which was comparable to 3.61 g/L butanol production measured using glucose. Moreover, the maximum production of biobutanol (0.38 g/L) was obtained at a PKC concentration of 30%, indicating the possibility of PKC utilization in butanol production. ABE fermentation of PKC using distilled water, TYA medium, and P2 medium showed that the highest butanol production (0.26 g/L) with ABE production of 0.38 g/L was obtained when ABE fermentation was conducted in P2 medium. [ABSTRACT FROM AUTHOR]

In this work, a new approach for acetone-butanol-ethanol (ABE) production has been proposed. Direct fermentation of native starches (uncooked process) was investigated by using granular starch hydrolyzing enzyme (GSHE) and Clostridium saccharoperbutylacetonicum N1-4. Even the process was carried out under suboptimal condition for activity of GSHE, the production of ABE was similar with that observed in conventional process or cooked process in terms of final solvent concentration (21.3 ± 0.4 to 22.4 ± 0.4 g/L), butanol concentration (17.5 ± 0.4 to 17.8 ± 0.3 g/L) and butanol yield (0.33 to 0.37 g/g). The production of solvents was significantly dependent on the source of starches. Among investigated starches, corn starch was more susceptible to GSHE while cassava starch was the most resistant to this enzyme. Fermentation using native corn starch resulted in the solvent productivity of 0.47 g/L h, which was about 15 % higher than that achieved in cooked process. On the contrary, uncooked process using cassava and wheat starch resulted in the solvent productivity of 0.30 and 0.37 g/L h, which were respectively about 30 % lower than those obtained in cooked process. No contamination was observed during all trials even fermentation media were prepared without sterilization. During the fermentation using native starches, no formation of foam is observed. This uncooked process does not require cooking starchy material; therefore, the thermal energy consumption for solvent production would remarkably be reduced in comparison with cooked process. [ABSTRACT FROM AUTHOR]

The anaerobic production of biohydrogen from different pretreated agroindustrial wastes, including rice bran (RB), de-oiled RB (DRB), sago starch (SS), and palm oil mill effluent (POME) via Clostridium saccharoperbutylacetonicum N1-4 was investigated in a batch culture system at 30 °C and a pH of 6.2. A yield of 7627, 6995, and 6,363 mL H/L was obtained from HSO (1 %)-treated DRB (10 %), enzymatically hydrolyzed DRB (10 %) and HCl (1 %)-treated DRB (10 %), respectively; however, untreated DRB (10 %) was able to produce only 3,286 mL H/L. A strategic treatment of RB (10 %) with HCl (1 %) followed by enzymatic hydrolysis could produce 3,172 mL H/L. An enzymatically hydrolyzed mixture of each POME and SS (5 %) produced 3,474 mL H/L, and a remarkable enhancement of H production (7,020 mL H/L) was achieved when the same mixture was subjected to XAD-4 resin treatment. In contrast, the enzymatically hydrolyzed SS (5 %) could produce only 4,628 mL H/L. Conclusively, it can be stated that agricultural wastes have a potential as substrates for biohydrogen production and that pretreatment with C. saccharoperbutylacetonicum N1-4 can contribute positively to enhancing the production. [ABSTRACT FROM AUTHOR]

Acetone–butanol–ethanol (ABE) fermentation using Clostridium saccharoperbutylacetonicum N1-4 and mixed sugars containing cellobiose and xylose was studied to establish efficient butanol production process without carbon catabolite repression (CCR). Although batch culture with glucose and xylose exhibited apparent CCR, we achieved simultaneous consumption of cellobiose and xylose. Moreover, preculture of the N1-4 strain with xylose yielded maximum butanol and solvent concentrations (16 and 23 g/L, respectively). Thus, we succeeded in ABE fermentation with mixed sugars of hexose and pentose, without CCR, by using wild-type ABE-producing clostridia. We also investigated the effect of various ratios of cellobiose and xylose on the fermentation process and yield. Increasing initial xylose concentration improved butanol and solvent concentrations and maximum xylose consumption rate. Fed-batch culture with cellobiose and xylose showed rapid and simultaneous sugar consumption and improved maximum consumption rate of both sugars. [ABSTRACT FROM AUTHOR]

Treated ricebran hydrolysate was fermented anaerobically using Clostridium saccharoperbutylacetonicum N1-4 at an initial pH of 6 ± 0.2 and an operating temperature of 30 °C for production of hydrogen. The effects of different pretreatment methods on the liberation of sugar from 100 g of ricebran per litre of medium (distilled water) were investigated. In addition, the effects of the pretreatment method on ricebran hydrolysates of different initial ricebran concentrations on liberated sugar as well as the effects of the initial inoculum concentration, ricebran (substrate) concentration, and FeSO4·7H2O concentration on the yield as well as the productivity of hydrogen were investigated. The combination of enzymatic hydrolysis and a boiling pretreatment method produced the most fermentable sugar, 29.03 ± 0.0 g/L from 100 g of ricebran per litre of medium (distilled water), while the amount of sugar liberated by ricebran hydrolysates of different initial ricebran concentrations upon pretreatment monotonically increased with the initial ricebran concentration. The increment in substrate, inoculum, and FeSO4·7H2O concentrations had a significantly positive effect (p < 0.05) on both the yield and productivity of hydrogen. The maximum hydrogen gas yield (Y P/S ) and productivity of 3.37 mol-H2 per mol-sugar consumed and 7.58 mmol/(L h), respectively, were obtained from ricebran hydrolysate with a 100 g/L ricebran concentration (equivalent to 28.59 ± 1.27 g sugar/L). In other experiments, 0.03 g/L FeSO4·7H2O and 1.5 g/L inoculum resulted in the best hydrogen gas yield and productivity from ricebran hydrolysates. [ABSTRACT FROM AUTHOR]

Abstract: A continuous butanol production system with high-density Clostridium saccharoperbutylacetonicum N1-4 generated by cell recycling was established to examine the characteristics of butanol fermentation from xylose. In continuous culture without cell recycling, cell washout was avoided by maintaining pH>5.6 at a dilution rate of 0.26h−1, indicating pH control was critical to this experiment. Subsequently, continuous culture with cell recycling increased cell concentration to 17.4gL−1, which increased butanol productivity to 1.20gL−1 h−1 at a dilution rate of 0.26h−1 from 0.529gL−1 h−1 without cell recycling. The effect of dilution rates on butanol production was also investigated in continuous culture with cell recycling. Maximum butanol productivity (3.32gL−1 h−1) was observed at a dilution rate of 0.78h−1, approximately 6-fold higher than observed in continuous culture without cell recycling (0.529gL−1 h−1). [Copyright &y& Elsevier]

We previously reported a butanol production process with pH-stat continuous feeding of dl-lactic acid and glucose as the co-substrate (Oshiro et al., Appl. Microbiol. Biotechnol., 87, 1177–1185, 2010). To accomplish butanol production from completely inedible substrates, in this study, we investigated acetone-butanol-ethanol (ABE) fermentation of Clostridium saccharoperbutylacetonicum N1-4 with lactic acid by using pentose as the co-substrate. Examination for optimum co-substrate indicated that arabinose was superior to glucose and xylose for ABE fermentation. Actually batch culture with lactic acid and arabinose without pH control exhibited higher butanol production (7.11 g/l) and lactic acid consumption (2.02 g) than those (6.62 g/l and 1.45 g, respectively) with glucose. Fed-batch culture without pH control increased these values to 12.08 g/l and 15.60 g/l butanol production, and to 3.83 g and 5.91 g lactic acid consumption by feeding the substrate once and twice, respectively. Finally, the result of gas chromatography–mass spectroscopy analysis using [1,2,3-13C3]-lactic acid indicated that lactic acid was converted to butanol with the efficiency of 51.9%. Thus, we established a novel high butanol production from lactic acid using arabinose as the co-substrate in simple fed-batch culture. [ABSTRACT FROM AUTHOR]

Palm oil mill effluent (POME) was used as an acetone-butanol-ethanol (ABE) fermentation medium using Clostridium saccharoperbutylacetonicum N1-4. Various pretreatment methods were applied on POME to increase the amount of fermentable sugars leading to enhanced ABE production. Sulfuric acid-treated POME (SA-POME) method was found to give the highest yield of total reducing sugars (glucose, cellobiose, xylose, and arabinose) as compared to other pretreatment methods. An increment in the concentration of HSO from 1 to 2% resulted in the enhanced release of reducing sugars (18.3, 26.3 g/L, respectively). However, the treatment of POME with 3% HSO, decreased the reducing sugars to 21.6 g/L and consequently, the total ABE production was also reduced. The highest yield of ABE was observed from a culture grown with POME treated by 1% HSO. The total ABE production from 1, 2, and 3% SA-POME was obtained as 2.2, 0.45, and 0.41 g/L, respectively. Although, enzymatically treated POME (EH-POME) could produce 4.42 g/L glucose, sulfuric acid treatment (1%) was able to liberate only 1.76 g/L glucose, ABE production was higher when 1% SA-POME was used. Low yield of ABE from enzymatically treated POME can be attributed to the production of some inhibitors during hydrolysis of POME. When EH-POME was treated with XAD-4 resin to nullify the inhibitors, the production of ABE was increased to 4.29 g/L, and ABE yield was also increased to 0.29 g/g. In conclusion, enzymatic hydeolysis of POME followed by elution to XAD-4 column can be proposed as the best pretreatment method for highest productivity of ABE. It was found that addition of P2 medium to the POME hydrolysates was able to improve the production of butanol except in raw POME and sulfuric acid hydrolysates. [ABSTRACT FROM AUTHOR]

Acetone-butanol-ethanol (ABE) was produced in Clostridium saccharoperbutylacetonicum N1-4 using sago starch as a substrate, and the effects of nutrient supplementation on ABE production were studied. Using sago starch as a substrate led to higher butanol production in C. saccharoperbutylacetonicum N1-4 when compared to other starchy materials as substrates. TYA medium supplemented with sago starch led to enhanced ABE and butanol production; however, P2 medium improved ABE production more than TYA medium. The highest ABE and butanol production was achieved with P2 medium supplemented with 70 g/L of sago starch. Using these fermentation conditions, ABE and butanol were produced at 16.65 and 9.83 g/L, respectively, and productivity was 0.15 g/L h for ABE and 0.09 g/L h for butanol. Using P2 medium supplemented with either 50 g/L enzymatically hydrolyzed sago starch or 70 g/L sago starch without hydrolysis, 9.81 and 9.83 g/L butanol were produced, respectively. These results reveal the importance of media formulation in the biobutanol fermentation of sago starch by C. saccharoperbutylacetonicum N1-4. [ABSTRACT FROM AUTHOR]

Abstract: A polytetrafluoroethylene (PTFE) membrane was used in membrane-assisted extractive (MAE) fermentation of acetone–butanol–ethanol (ABE) by Clostridium saccharoperbutylacetonicum N1-4. The growth inhibition effects of 1-dodecanol, which has a high partition coefficient for butanol, can be prevented by employing 1-dodecanol as an extractant when using a PTFE membrane. Compared to conventional fermentation, MAE–ABE fermentation with 1-dodecanol decreased butanol inhibition and increased glucose consumption from 59.4 to 86.0g/L, and total butanol production increased from 16.0 to 20.1g/L. The maximum butanol production rate increased from 0.817 to 0.979g/L/h. The butanol productivity per membrane area was remarkably high with this system, i.e., 78.6g/L/h/m2. Therefore, it is expected that this MAE fermentation system can achieve footprint downsizing. [Copyright &y& Elsevier]

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 (0-5 g/L) butyric acid and (0-10 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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In order to achieve high butanol production by Clostridium saccharoperbutylacetonicum N1-4, the effect of lactic acid on acetone–butanol–ethanol fermentation and several fed-batch cultures in which lactic acid is fed have been investigated. When a medium containing 20 g/l glucose was supplemented with 5 g/l of closely racemic lactic acid, both the concentration and yield of butanol increased; however, supplementation with more than 10 g/l lactic acid did not increase the butanol concentration. It was found that when fed a mixture of lactic acid and glucose, the final concentration of butanol produced by a fed-batch culture was greater than that produced by a batch culture. In addition, a pH-controlled fed-batch culture resulted in not only acceleration of lactic acid consumption but also a further increase in butanol production. Finally, we obtained 15.5 g/l butanol at a production rate of 1.76 g/l/h using a fed-batch culture with a pH-stat continuous lactic acid and glucose feeding method. To confirm whether lactic acid was converted to butanol by the N1-4 strain, we performed gas chromatography–mass spectroscopy (GC-MS) analysis of butanol produced by a batch culture during fermentation in a medium containing [1,2,3-13C3] lactic acid as the initial substrate. The results of the GC-MS analysis confirmed the bioconversion of lactic acid to butanol. [ABSTRACT FROM AUTHOR]

Abstract: A kinetic simulation model of metabolic pathways that describes the dynamic behaviors of metabolites in acetone–butanol–ethanol (ABE) production by Clostridium saccharoperbutylacetonicum N1-4 was proposed using a novel simulator WinBEST-KIT. This model was validated by comparing with experimental time-course data of metabolites in batch cultures over a wide range of initial glucose concentrations (36.1–295mM). By introducing substrate inhibition, product inhibition of butanol, activation of butyrate and considering the cessation of metabolic reactions in the case of insufficiency of energy after glucose exhaustion, the revised model showed 0.901 of squared correlation coefficient (r 2) between experimental time-course of metabolites and calculated ones. Thus, the final revised model is assumed to be one of the best candidates for kinetic simulation describing dynamic behavior of metabolites in ABE production. Sensitivity analysis revealed that 5% increase in reaction of reverse pathway of butyrate production (R 17) and 5% decrease in reaction of CoA transferase for butyrate (R 15) highly contribute to high production of butanol. These system analyses should be effective in the elucidation which pathway is metabolic bottleneck for high production of butanol. [Copyright &y& Elsevier]

A pH-stat fed-batch culture by feeding butyric acid and glucose has been studied in an acetone–butanol–ethanol (ABE) fermentation using Clostridium saccharoperbutylacetonicum N1-4. The specific butanol production rate increased from 0.10 g-butanol/g-cells/h with no feeding of butyric acid to 0.42 g-butanol/g-cells/h with 5.0 g/l butyric acid. The pH value in broth decreases with butyric acid production during acidogenesis, and then butyric acid reutilization and butanol production result in a pH increase during solventogensis. The pH-stat fed-batch culture was performed to maintain a constant pH and butyric acid concentration in the culture broth, but feeding only butyric acid could not support butyric acid utilization and butanol production. Subsequently, when a mixture of butyric acid and glucose was fed, butyric acid was utilized and butanol was produced. To investigate the effect of the feeding ratio of butyric acid to glucose (B/G ratio), several B/G ratio solutions were fed. The maximum butanol production was 16 g/l and the residual glucose concentration in broth was very low at a B/G ratio of 1.4. Moreover, yields of butanol in relation to cell mass and glucose utilization were 54% and 72% higher in pH-stat fed-batch culture with butyric acid than that of conventional batch culture, respectively. [Copyright &y& Elsevier]