Reducing cofactors contribute to the increase of butanol production by a wild-type Clostridium sp. strain BOH3

Enhancement of biohydrogen production in Clostridium acetobutylicum ATCC 824 by overexpression of glyceraldehyde-3-phosphate dehydrogenase gene

In the dark fermentation of hydrogen, development of production host is crucial as bacteria act on substrates and produce hydrogen. The present study aimed to improve hydrogen production through the development of Clostridium acetobutylicum as a superior biohydrogen producer. Glyceraldehyde-3-phosphate dehydrogenase (GAPDH), which produces NADH/NADPH for metabolites and energy in primary pathways, was introduced to enhance hydrogen production. The strain CAC824-G containing gapC that encodes GAPDH showed a 66.3 % higher hydrogen production than the wild-type strain, with increased NADH and NADPH pools. Glucose consumption and other byproducts, such as acetone, butanol, and ethanol, were also high in CAC824-G. Overexpression of gapC resulted in increased hydrogen production with sugars obtained from different biomass, even in the presence of inhibitors such as vanillin, 5-hydroxymethylfufural, acetic acid, and formic acid. Our results imply that overexpression of gapC in Clostridium is possible to expand the production of the reported biochemicals to produce hydrogen.

Production of acetone, butanol, and ethanol by electro-fermentation with Clostridium saccharoperbutylacetonicum N1-4

This manuscript describes the effect of altering the extracellular redox potential during the production of acetone, butanol, and ethanol on a dual chamber H-type microbial fuel cell by fermenting glucose with Clostridium saccharoperbutylacetonicum N1-4. Extracellular redox potential modification was achieved by either supplementing the microbial broth with the redox agent NADH or by poising the cathode potential at -600 mV vs. Ag/AgCl. The addition of NADH was found to foment the production of acetone via fermentation of glucose. The addition of 200 mM of NADH to the catholyte rendered the highest production of acetone (2.4 g L^-1), thus outperforming the production of acetone by conventional fermentation means (control treatment) by a factor of 2.2. The experimental evidence gathered here, indicates that cathodic electro-fermentation of glucose favors the production of butanol. When poising the cathode potential at -600 mV vs Ag/AgCl (electro-fermentation), the largest production of butanol was achieved (5.8 g L^-1), outperforming the control treatment by a factor of 1.5. The production of ABE solvents and the electrochemical measurements demonstrate the electroactive properties of C. saccharoperbutylacetonicum N1-4 and illustrates the usefulness of bio-electrochemical systems to improve conventional fermentative processes.

Sodium formate redirects carbon flux and enhances heterologous mevalonate production in Methylobacterium extorquens AM1

Methylobacterium extorquens AM1 (AM1), a model strain of methylotrophic cell factories (MeCFs) could be used to produce fine chemicals from methanol. Synthesis of heterologous products usually needs reducing cofactors, but AM1 growing on methanol lack reducing power. Formate could be used as a reducing agent. In this study, mevalonic acid (MEV) yield of 0.067 gMEV/g methanol was reached by adding 10 mmol L^-1 sodium formate in MEV accumulating stage (at 72 h). The yield was improved by 64.57%, and represented the highest yield reported to date. ¹³ C-labeling experiments revealed global effects of sodium formate on metabolic pathways in engineered Methylobacterium extorquens AM1. Sodium formate significantly increased the ratios of reducing equivalents, enhanced the metabolic rate of pathways demanding reducing cofactors and redirected the carbon flux to MEV synthesis. As a result, coupling formate to methanol-based production provide a promising way for converting C1 substances to useful chemical products.

Efficient Synthesis of Phycocyanobilin by Combinatorial Metabolic Engineering in Escherichia coli

Phycocyanobilin (PCB) is a kind of light-harvesting pigment which naturally exists in algae and plays important roles in absorbing and transferring energy. Based on its antioxidant and optical properties, PCB has been applied in food, medicine, and cosmetics. Currently, PCB is mainly extracted from Spirulina through complicated steps; thus, the biosynthesis of PCB in Escherichia coli has attracted more attention. However, due to the lower catalytic efficiency of synthetic enzymes and the deficiency of precursors and cofactors, the titer of PCB remains at a low level. Here, we report the efficient synthesis of PCB by the expression of heme oxygenase-1 from Thermosynechococcus elongatus and PCB: ferredoxin oxidoreductase (PcyA) from Synechocystis sp. using a high-copy number plasmid with an inducible T7lac promoter and the assembly of these two enzymes at a suitable ratio of 2:1 with DNA scaffolds. Additionally, the synthesis of PCB was further enhanced by direct supplementation of 5-aminolevulinic acid (ALA), moderate overexpression of key enzymes in the heme biosynthetic pathway (hemB and hemH), and accelerated cycle of cofactors (NADPH) through the expression of NAD⁺ kinase and the addition of a reducing agent. Finally, based on the optimal conditions (Modified R medium with 200 mg/L ALA, 20 mg/L FeSO₄·7H₂O, and 5 g/L vitamin C induced by 0.8 mM isopropylthio-β-galactoside at 30 °C), the highest reported titer of PCB (28.32 mg/L) was obtained at the fermenter level by feeding glucose and FeSO₄·7H₂O. The strategies applied in this study will be useful for the synthesis of other natural pigments and PCB or heme derivatives in E. coli.

Production of butanol from distillers' grain waste by a new aerotolerant strain of Clostridium beijerinckii LY-5

A new aerotolerant strain of Clostridium beijerinckii LY-5 was isolated from the pit mud of the Chinese Baijiu-making process for butanol production. Plackett-Burman design and artificial neural network were used to optimize the fermentation medium and a total of 13.54 ± 0.22 g/L butanol and 19.91 ± 0.52 g/L ABE were attained under aerotolerant condition. Moreover, distillers' grain waste (DGW), the main by-product in the Baijiu production process, was utilized as potential substrate for butanol production. DGW was hydrolyzed by α-amylase and glucoamylase and then fermented after a detoxifying process of overliming. Butanol and ABE concentrations were 9.02 ± 0.18 and 9.57 ± 0.19 g/L with the yield of 0.21 and 0.23 g/g sugar, respectively. The higher ratio of butanol to ABE might be caused by the inhibitors in DGW medium affecting the metabolic pathways of C. beijerinckii LY-5 and approximately 1.48 ± 0.04 g/L isopropanol was found at the end of fermentation. This work highlights the feasibility of using DGW as a promising feedstock for butanol production by a new aerotolerant strain of C. beijerinckii LY-5, with benefit to the environment.

Transcriptomic and Phenotypic Analysis of a spoIIE Mutant in Clostridium beijerinckii

SpoIIE is a phosphatase involved in the activation of the first sigma factor of the forespore, σ F , during sporulation. A ΔspoIIE mutant of Clostridium beijerinckii NCIMB 8052, previously generated by CRISPR-Cas9, did not sporulate but still produced granulose and solvents. Microscopy analysis also showed that the cells of the ΔspoIIE mutant are elongated with the presence of multiple septa. This observation suggests that in C. beijerinckii, SpoIIE is necessary for the completion of the sporulation process, as seen in Bacillus and Clostridium acetobutylicum. Moreover, when grown in reactors, the spoIIE mutant produced higher levels of solvents than the wild type strain. The impact of the spoIIE inactivation on gene transcription was assessed by comparative transcriptome analysis at three time points (4 h, 11 h and 23 h). Approximately 5% of the genes were differentially expressed in the mutant compared to the wild type strain at all time points. Out of those only 12% were known sporulation genes. As expected, the genes belonging to the regulon of the sporulation specific transcription factors (σ F , σ E , σ G , σ K ) were strongly down-regulated in the mutant. Inactivation of spoIIE also caused differential expression of genes involved in various cell processes at each time point. Moreover, at 23 h, genes involved in butanol formation and tolerance, as well as in cell motility, were up-regulated in the mutant. In contrast, several genes involved in cell wall composition, oxidative stress and amino acid transport were down-regulated. These results indicate an intricate interdependence of sporulation and stationary phase cellular events in C. beijerinckii.

Transcriptional analysis of amino acid, metal ion, vitamin and carbohydrate uptake in butanol-producing Clostridium beijerinckii NRRL B-598

In-depth knowledge of cell metabolism and nutrient uptake mechanisms can lead to the development of a tool for improving acetone-butanol-ethanol (ABE) fermentation performance and help to overcome bottlenecks in the process, such as the high cost of substrates and low production rates. Over 300 genes potentially encoding transport of amino acids, metal ions, vitamins and carbohydrates were identified in the genome of the butanol-producing strain Clostridium beijerinckii NRRL B-598, based on similarity searches in protein function databases. Transcriptomic data of the genes were obtained during ABE fermentation by RNA-Seq experiments and covered acidogenesis, solventogenesis and sporulation. The physiological roles of the selected 81 actively expressed transport genes were established on the basis of their expression profiles at particular stages of ABE fermentation. This article describes how genes encoding the uptake of glucose, iron, riboflavin, glutamine, methionine and other nutrients take part in growth, production and stress responses of C. beijerinckii NRRL B-598. These data increase our knowledge of transport mechanisms in solventogenic Clostridium and may be used in the selection of individual genes for further research.

Enhanced Biobutanol Production in Folic Acid-Induced Medium by Using Clostridium acetobutylicum NRRL B-527

The conventional acetone-butanol-ethanol fermentation process suffers from several key hurdles viz. low solvent titer, insufficient yield and productivity, and solvent intolerance which largely affect butanol commercialization. To counteract these issues, the effect of stimulator, namely, folic acid was investigated in the present study to improve butanol titer. Folic acid is involved in biosynthesis of a diverse range of cellular components, which subsequently alter the amino acid balance. Therefore, different concentrations of folic acid were screened, and 10 mg/L supplementation resulted in a maximum butanol production of 10.78 ± 0.09 g/L with total solvents of 18.91 ± 0.21 g/L. Folic acid addition at different time intervals was also optimized to get additional improvements in final butanol concentration. Overall, folic acid supplementation resulted in two-fold increase in butanol concentration and thus could be considered as a promising strategy to enhance solvent titers.

Effect of Operating Conditions and Immobilization on Butanol Enhancement in an Extractive Fermentation Using Non-ionic Surfactant

The present study was undertaken in order to investigate effect of diverse parameters such as fermentation media, pH, initial concentration of biomass, different surfactant concentrations, and immobilization on increasing butanol and total solvent production. Cheng's fermentation media was successfully tested and perceived to increase final solvents concentration. Controlled pH at 12th and 24th hours had negative effect on butanol enhancement; however, it resulted in more butyric acid production which remained accumulated. Ten percent (v/v) biomass was evaluated to increase final solvents concentration and hence butanol yield compared to 20% and 30% (v/v) of initial biomass concentrations. Effect of surfactant concentration (3-20%) was studied on butanol production. Six percent (v/v) L62 resulted in 49% higher final butanol concentration compared to control. Simultaneous immobilization and fermentation showed higher butanol production (16.8 g/L with 6%) which was attributed to partial immobilization of biomass.

Role of Trace Elements as Cofactor: An Efficient Strategy toward Enhanced Biobutanol Production

Metabolic engineering has the potential to steadily enhance product titers by inducing changes in metabolism. Especially, availability of cofactors plays a crucial role in improving efficacy of product conversion. Hence, the effect of certain trace elements was studied individually or in combinations, to enhance butanol flux during its biological production. Interestingly, nickel chloride (100 mg L^-1) and sodium selenite (1 mg L^-1) showed a nearly 2-fold increase in solvent titer, achieving 16.13 ± 0.24 and 12.88 ± 0.36 g L^-1 total solvents with yields of 0.30 and 0.33 g g^-1, respectively. Subsequently, the addition time (screened entities) was optimized (8 h) to further increase solvent production up to 18.17 ± 0.19 and 15.5 ± 0.13 g L^-1 by using nickel and selenite, respectively. A significant upsurge in butanol dehydrogenase (BDH) levels was observed, which reflected in improved solvent productions. Additionally, a three-dimensional structure of BDH was also constructed using homology modeling and subsequently docked with substrate, cofactor, and metal ion to investigate proper orientation and molecular interactions.

Unique genetic cassettes in a Thermoanaerobacterium contribute to simultaneous conversion of cellulose and monosugars into butanol

The demand for cellulosic biofuels is on the rise because of the anticipation for sustainable energy and less greenhouse gas emissions in the future. However, production of cellulosic biofuels, especially cellulosic butanol, has been hampered by the lack of potent microbes that are capable of converting cellulosic biomass into biofuels. We report a wild-type Thermoanaerobacterium thermosaccharolyticum strain TG57, which is capable of using microcrystalline cellulose directly to produce butanol (1.93 g/liter) as the only final product (without any acetone or ethanol produced), comparable to that of engineered microbes thus far. Strain TG57 exhibits significant advances including unique genes responsible for a new butyrate synthesis pathway, no carbon catabolite repression, and the absence of genes responsible for acetone synthesis (which is observed as the main by-product in most Clostridium strains known today). Furthermore, the use of glucose analog 2-deoxyglucose posed a selection pressure to facilitate isolation of strain TG57 with deletion/silencing of carbon catabolite repressor genes-the ccr and xylR genes-and thus is able to simultaneously ferment glucose, xylose, and arabinose to produce butanol (7.33 g/liter) as the sole solvent. Combined analysis of genomic and transcriptomic data revealed unusual aspects of genome organization, numerous determinants for unique bioconversions, regulation of central metabolic pathways, and distinct transcriptomic profiles. This study provides a genome-level understanding of how cellulose is metabolized by T. thermosaccharolyticum and sheds light on the potential of competitive and sustainable biofuel production.

Enhanced robustness in acetone-butanol-ethanol fermentation with engineered Clostridium beijerinckii overexpressing adhE2 and ctfAB

Clostridium beijerinckii CC101 was engineered to overexpress aldehyde/alcohol dehydrogenase (adhE2) and CoA-transferase (ctfAB). Solvent production and acid assimilation were compared between the parental and engineered strains expressing only adhE2 (CC101-SV4) and expressing adhE2, ald and ctfAB (CC101-SV6). CC101-SV4 showed an early butanol production from glucose but stopped pre-maturely at a low butanol concentration of ∼6g/L. Compared to CC101, CC101-SV6 produced more butanol (∼12g/L) from glucose and was able to re-assimilate more acids, which prevented "acid crash" and increased butanol production, under all conditions studied. CC101-SV6 also showed better ability in using glucose and xylose present in sugarcane bagasse hydrolysate, and produced 9.4g/L solvents (acetone, butanol and ethanol) compared to only 2.6g/L by CC101, confirming its robustness and better tolerance to hydrolysate inhibitors. The engineered strain of C. beijerinckii overexpressing adhE2 and ctfAB should have good potential for producing butanol from lignocellulosic biomass hydrolysates.

High-yield production of mannitol by Leuconostoc pseudomesenteroides CTCC G123 from chicory-derived inulin hydrolysate

Chicory is an agricultural plant with considerable potential as a carbohydrate substrate for low-cost production of biochemicals. In this work, the production of mannitol by Leuconostoc pseudomesenteroides CTCC G123 from chicory-derived inulin hydrolysate was investigated. The bioconversion process initially suffered from the leakage of fructose to the phosphoketolase pathway, resulting in a low mannitol yield. When inulin hydrolysate was supplemented with glucose as a substrate for mannitol production in combination with aeration induction and nicotinic acid induced redox modulation strategies, the mannitol yield greatly improved. Under these conditions, significant improvement in the glucose consumption rate, intracellular NADH levels and mannitol dehydrogenase specific activity were observed, with mannitol production increasing from 64.6 to 88.1 g/L and overall yield increase from 0.69 to 0.94 g/g. This work demonstrated an efficient method for the production of mannitol from inulin hydrolysate with a high overall yield.

Waste-to-biofuel: production of biobutanol from sago waste residues

The main concern of extensive production of biobutanol has been associated with the high cost of the substrate and the relatively low tolerance of Clostridia to biobutanol production. In this study, the use of fermentable cassava waste residue (CWR) as substrate for biobutanol production was investigated using solvent-tolerant Clostridium sp. Four of obligatory, solvent-producing bacteria were isolated from sago industry waste sites. The NSW, PNAS1, SB5 and SBI4 strains showed identical profiles of 16S rRNA gene sequence similarity of Bacillus coagulans, Clostridium bifermentans and Clostridium sp. (97% similarity) and a wide range of carbohydrate substrate; however, the CWR was found to be suitable for the production of biobutanol considerably. Batch culture study was carried out using parameters such as time and temperature and carbon sources have been studied and optimized. Using pre-optimized CWR medium, significant amount of solvent production was observed in NSW, PNAS1, SB5 and SBI4 with 1.53, 3.36, 1.56 and 2.5 g L^-1of butanol yield and 6.84, 9.012, 8.32 and 8.22 g L^-1of total solvents, respectively. On the basis of these studies, NSW is proposed to represent the B. coagulans for butanol production directly from sago waste residues.

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.

Substrate dependent modulation of butanol to ethanol ratio in non-acetone forming Clostridium sporogenes NCIM 2918

Present study reports a non-acetone producing Clostridium sporogenes strain as a potential producer of liquid biofuels. Alcohol production was positively regulated by sorbitol and instant dry yeast as carbon and nitrogen sources respectively. Media optimization resulted in maximum butanol and ethanol titer (gL^-1) of 12.1 and 7.9 respectively. Depending on the combination of carbon sources, the organism was found to manipulate its metabolism towards synthesis of either ethanol or butanol, thereby affecting the total alcohol titer. Among various dual substrate combinations, glucose-glycerol mixture in the ratio of 60:40 resulted in maximum butanol and ethanol titer (gL^-1) of 11.9 and 12.1 respectively with total alcohol productivity of 0.59gL^-1h^-1. In the mixture, when pure glycerol was replaced with crude glycerol, butanol and ethanol titer (gL^-1) of 11.2 and 11.7 was achieved. Hence, the strain shows immense potential for biofuels production using crude glycerol as cheap substrate.

Simultaneous saccharification and fermentation of hemicellulose to butanol by a non-sporulating Clostridium species

Production of lignocellulosic butanol has drawn increasing attention. However, currently few microorganisms can produce biofuels, particularly butanol, from lignocellulosic biomass via simultaneous saccharification and fermentation. Here we report discovery of a wild-type, mesophilic Clostridium sp. strain MF28 that ferments xylan to produce butanol (up to 3.2g/L) without the addition of saccharolytic enzymes and without any chemical pretreatments. Application of selective pressure from 2-deoxy-d-glucose facilitated isolation of strain MF28, which exhibits inactivation of genes (gid and ccp genes) responsible for carbon catabolite repression, thus allowing strain MF28 to simultaneously ferment a combination of glucose (30g/L), xylose (15g/L), and arabinose (15g/L) to produce 11.9g/L of butanol. Strain MF28 possesses several unique features: (i) non-sporulating, (ii) no acetone/ethanol, (iii) complete hemicellulose-binding enzymatic domain, and (iv) absence of carbon catabolite repression. These unique characteristics demonstrate the industrial potential of strain MF28 for cost-effective biofuel generation from lignocellulosic biomass.

Enhanced butanol fermentation using metabolically engineered Clostridium acetobutylicum with ex situ recovery of butanol

In this study, metabolic target reactions for strain engineering were searched via intracellular coenzyme A (CoA) metabolite analysis. The metabolic reactions catalyzed by thiolase (AtoB) and aldehyde-alcohol dehydrogenase (AdhE1) were considered potential rate-limiting steps. In addition, CoA transferase (CtfAB) was highlighted as being important for the assimilation of organic acids, in order to achieve high butanol production. Based on this quantitative analysis, the BEKW_E1AB-atoB strain was constructed by overexpressing the thl (atoB), adhE1, and ctfAB genes in Clostridium acetobutylicum strain BEKW, which has the phosphotransacetylase (pta) and butyrate kinase (buk) genes knocked out. After 100h of continuous fermentation coupled with adsorptive ex situ butanol recovery, the concentrations found after considering desorption, yield, and productivity for the BEKW_E1AB-atoB strain were 55.7g/L, 0.38g/g, and 2.64g/L/h, respectively. The level of butanol production achieved (2.64g/L/h) represents the highest reported value obtained after adsorptive, long-term fermentation.

Using tobacco waste extract in pre-culture medium to improve xylose utilization for l-lactic acid production from cellulosic waste by Rhizopus oryzae

The aim of this work was to study the high-titer l-lactic acid production from cellulosic waste using Rhizopus oryzae. The tobacco waste water-extract (TWE) added with 5g/L glucose and 0.1g/L vitamin C was optimized as pre-culture medium for R. oryzae. Results found that compared to traditional pre-culture medium, it improved xylose consumption rate up to 2.12-fold and enhanced l-lactic acid yield up to 1.73-fold. The highest l-lactic acid concentration achieved was 173.5g/L, corresponding to volumetric productivity of 1.45g/Lh and yield of 0.860g/g total reducing sugar in fed-batch fermentation. This process achieves efficient production of polymer-grade l-lactic acid from cellulosic feedstocks, lowers the cost of fungal cell pre-culture and provides a novel way for re-utilization of tobacco waste.

Strategies for production of butanol and butyl-butyrate through lipase-catalyzed esterification

In this study, a fermentation process for production of butanol and butyl-butyrate by using Clostridium sp. strain BOH3 is developed. This strain is able to produce butyric acid and butanol when it ferments 60 g/L xylose. Meanwhile, it also excreted indigenous lipases (induced by olive oil) which naturally convert butyric acid and butanol into 1.2 g/L of butyl-butyrate. When Bio-OSR was used as both an inducer for lipase and extractant for butyl-butyrate, the butyl-butyrate concentration can reach 6.3 g/L. To further increase the yield, additional lipases and butyric acid are added to the fermentation system. Moreover, kerosene was used as an extractant to remove butyl-butyrate in situ. When all strategies are combined, 22.4 g/L butyl-butyrate can be produced in a fed-batch reactor spiked with 70 g/L xylose and 7.9 g/L butyric acid, which is 4.5-fold of that in a similar system (5 g/L) with hexadecane as the extractant.

A metabolic-based approach to improve xylose utilization for fumaric acid production from acid pretreated wheat bran by Rhizopus oryzae

In this work, wheat bran (WB) was utilized as feedstock to synthesize fumaric acid by Rhizopus oryzae. Firstly, the pretreatment process of WB by dilute sulfuric acid hydrolysis undertaken at 100°C for 30min offered the best performance for fumaric acid production. Subsequently, through optimizing the seed culture medium, a suitable morphology (0.55mm pellets diameter) of R. oryzae was obtained. Furthermore, a metabolic-based approach was developed to profile the differences of intracellular metabolites concentration of R. oryzae between xylose (the abundant sugar in wheat bran hydrolysate (WBH)) and glucose metabolism. The xylitol, sedoheptulose 7-phosphate, ribulose 5-phosphate, glucose 6-phosphate, proline and serine were responsible for fumaric acid biosynthesis limitation in xylose fermentation. Consequently, regulation strategies were proposed, leading to a 149% increase in titer (up to 15.4g/L). Finally, by combinatorial regulation strategies the highest production was 20.2g/L from WBH, 477% higher than that of initial medium.

Enhanced direct fermentation of cassava to butanol by Clostridium species strain BOH3 in cofactor-mediated medium

BACKGROUND

The main challenge of cassava-based biobutanol production is to enhance the simultaneous saccharification and fermentation with high hyperamylolytic activity and butanol yield. Manipulation of cofactor [e.g., Ca(2+) and NAD/(P)H] levels as a potential tool to modulate carbon flux plays a key role in the cassava hydrolysis capacity and butanol productivity. Here, we aimed to develop a technology for enhancing butanol production with simultaneous hydrolysis of cassava (a typical model as a non-cereal starchy material) using a cofactor-dependent modulation method to maximize the production efficacy of biobutanol by Clostridium sp. stain BOH3.

RESULTS

Supplementing CaCO3 to the medium containing cassava significantly promotes activities of α-amylase responsible for cassava hydrolysis and butanol production due to the role of Ca(2+) cofactor-dependent pathway in conversion of cassava starch to reducing sugar and its buffering capacity. Also, after applying redox modulation with l-tryptophan (a precursor as de novo synthesis of NADH and NADPH), the levels of cofactor NADH and NADPH increased significantly by 67 % in the native cofactor-dependent system of the wild-type Clostridium sp. stain BOH3. Increasing availability of NADH and NADPH improved activities of NADH- and NADPH-dependent butanol dehydrogenases, and thus could selectively open the valve of carbon flux toward the more reduced product, butanol, against the more oxidized acid or acetone products. By combining CaCO3 and l-tryptophan, 17.8 g/L butanol with a yield of 30 % and a productivity of 0.25 g/L h was obtained with a hydrolytic capacity of 88 % towards cassava in a defined medium. The metabolic patterns were shifted towards more reduced metabolites as reflected by higher butanol-acetone ratio (76 %) and butanol-bioacid ratio (500 %).

CONCLUSIONS

The strategy of altering enzyme cofactor supply may provide an alternative tool to enhance the stimulation of saccharification and fermentation in a cofactor-dependent production system. While genetic engineering focuses on strain improvement to enhance butanol production, cofactor technology can fully exploit the productivity of a strain and maximize the production efficiency.

Production of butanol by Clostridium saccharoperbutylacetonicum N1-4 from palm kernel cake in acetone-butanol-ethanol fermentation using an empirical model

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 0.1g/L butanol was obtained. Butanol production was enhanced by diluting PKC hydrolysate up to 70% in which 3.59g/L butanol was produced.