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Abstract: Xylitol was used as a raw material for production of l-xylose and l-lyxose using Alcaligenes 701B strain and immobilized l-rhamnose isomerase enzyme. Alcaligenes 701B converted xylitol to l-xylulose with a yield of 34% in the bioreactor. l-Xylulose was converted to l-xylose and l-lyxose using immobilized l-rhamnose isomerase enzyme. The final equilibrium between l-xylulose, l-xylose and l-lyxose was 53:26:21. The enzyme assays indicated that Alcaligenes 701B strain has an NAD-dependent xylitol dehydrogenase enzyme responsible for l-xylulose production. Furthermore, NAD(P)H-dependent l-xylulose reductase enzyme was active during conversion of xylitol to l-xylulose. The highest l-xylulose production rate corresponded with the highest growth rate. The Alcaligenes 701B strain used d-xylose for biomass growth, but xylitol was used only for l-xylulose production during conversion phase. [Copyright &y& Elsevier]

The biomass obtained after the extraction of forskolin from the roots of Coleus forskohlii was evaluated as a substrate for the production of acetone-butanol-ethanol (ABE). The spent biomass constituting more than 90% of the raw material showed 50–70% carbohydrates with starch and cellulose being the major constituents. This study was undertaken to optimize enzymatic hydrolysis of C. forskohlii roots for maximum release of fermentable sugars and subsequent fermentation to ABE. The root biomass was hydrolyzed using the Stargen ® 002 and Accellerase ® 1500. Cocktail of both enzymes (16U Stargen ® 002 and 60 FPU Accellerase ® 1500) could produce 41.2 g/l of total reducing sugars (glucose equivalent to 32.33 g/l). The production of ABE was optimized in a batch fermentation using Clostridium acetobutylicum NCIM 2877. The maximum ABE production using the root hydrolysates was 0.55 g/l. Pretreatment with lime and Amberlite XAD-4 increased the production of total solvent to 5.33 g/l. [ABSTRACT FROM AUTHOR]

Acetone being a non-fuel solvent produced during the traditional acetone-butanol-ethanol (ABE) fermentation by Clostridium acetobutylicum ; reduces the overall fuel alcohol yield. However, the conversion of acetone into isopropanol has been recommended to improve the process economy. The present study aims to develop an engineered C. acetobutylicum DSM 792 strain to convert acetone into isopropanol by introducing the secondary alcohol dehydrogenase gene from Clostridium beijerinckii NRRL B593 using the allele-coupled exchange approach. Batch and continuous fermentation experiments were carried out with a modified strain C. acetobutylicum DSM 792-ADH to improve the isopropanol yield and titer. The growth and production behavior of the modified strain in stationary flask culture and controlled batch culture was studied. Almost 50% of acetone was converted into isopropanol with highest total solvent yield to be 0.39 g g −1 glucose. The modified strain also utilized sugar mixture and SO 2 –ethanol–water spent liquor as a substrate to produce the solvents. [ABSTRACT FROM AUTHOR]

The co-production of acetone during traditional butanol fermentation (acetone–butanol–ethanol) lowers the yield of alcohol biofuels. The present study was aimed to develop an improved Clostridium acetobutylicum strain with enhanced alcohol fuel production capability. The previously developed IBE (isopropanol-butanol-ethanol) producing C. acetobutylicum DSM792-ADH strain was further optimized to enhance the solvent productivity and yield. Immobilized cell column reactor was used to investigate the effect of dilution rate on IBE fermentation. Pure glucose, artificial sugar mixture and SEW spent liquor from spruce chips were used as substrates to study the behavior of the modified microorganism. The highest total solvent concentrations of approximately 10.60 g l −1 , 10 g l −1 and 6 g l −1 were obtained when glucose, sugar mixture and SEW spent liquor were used as substrates respectively. The modified microorganism could effectively utilize the lignocellulosic biomass hydrolyzate (SEW spent liquor) to yield a solvent productivity of 1.67 g l −1 h −1 . [ABSTRACT FROM AUTHOR]

Highlights: [•] Carbohydrate profiling of Coleus forskohlii root. [•] Utilization of Coleus forskohlii root biomass for bioethanol production. [•] Immobilization of yeast on wood chips. [•] Continuous lignocellulosic fermentation to produce bioethanol. [ABSTRACT FROM AUTHOR]

Highlights: [•] Study suggests the preference of biomass feedstocks appropriate for ABE-fermentation. [•] Effect of varying lignocellulosic sugar concentrations in continuous column reactor. [•] Multi linear regression (MLR) modeling successfully used for continuous production of solvents. [•] Scale up of column reactor is successfully demonstrated. [Copyright &y& Elsevier]

Highlights: [•] Oil palm empty fruit bunches (OPEFB) are fractionated by SO2–ethanol–water mixture. [•] Fractionation of OPEFB feedstock produces cellulosic fibers and spent liquor. [•] Spent liquor contains dissolved hemicellulose sugars (mostly monomers) and lignin. [•] Fractionation and sugar hydrolysis is hindered by the high cation content of OPEFB. [•] Acidic leaching of OPEFB only partly removes cations; more intense deashing needed. [Copyright &y& Elsevier]

Highlights: [•] Advanced and economical production of biobutanol. [•] Continuous two stage fermentation with integrated liquid–liquid recovery technique. [•] Utilization of lignocellulosic sugar mixture (pentoses and hexoses). [•] Long run system operation with high solvent productivity (10.85g/Lh) and yield. [•] Can be integrated to the wood based biorefinery to make it industrially feasible. [ABSTRACT FROM AUTHOR]

Abstract: A process for the fermentative production of propionic acid from whole wheat flour using starch and gluten as nutrients is presented. Hydrolysis of wheat flour starch using amylases was optimized. A batch fermentation of hydrolysate supplemented with various nitrogen sources using Propionibacterium acidipropionici NRRL B 3569 was performed. The maximum production of 48.61, 9.40, and 11.06g of propionic acid, acetic acid and succinic acid, respectively, was found with wheat flour hydrolysate equivalent to 90g/l glucose and supplemented with 15g/l yeast extract. Further, replacement of yeast extract with wheat gluten hydrolysate showed utilization of gluten hydrolysate without compromising the yields and also improving the economics of the process. The process so developed could be useful for production of animal feed from whole wheat with in situ production of preservatives, and also suggest utilization of sprouted or germinated wheat for the production of organic acids. [Copyright &y& Elsevier]

Abstract: The present study proposes the use of market rejected and waste vegetables as a supplement for improved acetone–ethanol–butanol (ABE) solvent production. In the present study, three different perishable vegetables were evaluated as supplements for ABE fermentation. These vegetables were found to stimulate the solvent production at as low as 1% (w/v) concentration. The supplementation showed improved production of solvents using 4-fold diluted SO2–ethanol–water (SEW) spent liquor supplemented with 25g/l glucose as a substrate. The maximum total solvent production obtained with 5% (w/v) supplementation of carrot, cabbage and tomato was 9.96g/l, 10.49g/l and 10.65g/l, respectively as compared to the control value of 7.43g/l. The applicability of vegetables was successfully evaluated as a complex medium for solvent production. [Copyright &y& Elsevier]

Abstract: The objective of this study was to optimize continuous acetone–butanol–ethanol (ABE) fermentation using a two stage chemostat system integrated with liquid–liquid extraction of solvents produced in the first stage. This minimized end product inhibition by butanol and subsequently enhanced glucose utilization and solvent production in continuous cultures of Clostridium acetobutylicum B 5313. During continuous two-stage ABE fermentation, sugarcane bagasse was used as the cell holding material for the both stages and liquid–liquid extraction was performed using an oleyl alcohol and decanol mixture. An overall solvent production of 25.32g/L (acetone 5.93g/L, butanol 16.90g/L and ethanol 2.48g/L) was observed as compared to 15.98g/L in the single stage chemostat with highest solvent productivity and solvent yield of 2.5g/Lh and of 0.35g/g, respectively. Maximum glucose utilization (83.21%) at a dilution rate of 0.051/h was observed as compared to 54.38% in the single stage chemostat. [Copyright &y& Elsevier]

Abstract: SO2–ethanol–water (SEW) spent liquor from spruce chips was successfully used for batch and continuous production of acetone, butanol and ethanol (ABE). Initially, batch experiments were performed using spent liquor to check the suitability for production of ABE. Maximum concentration of total ABE was found to be 8.79g/l using 4-fold diluted SEW liquor supplemented with 35g/l of glucose. The effect of dilution rate on solvent production, productivity and yield was studied in column reactor consisting of immobilized Clostridium acetobutylicum DSM 792 on wood pulp. Total solvent concentration of 12g/l was obtained at a dilution rate of 0.21h−1. The maximum solvent productivity (4.86g/lh) with yield of 0.27g/g was obtained at dilution rate of 0.64h−1. Further, to increase the solvent yield, the unutilized sugars were subjected to batch fermentation. [Copyright &y& Elsevier]

Abstract: A novel facultative thermophilic bacterium capable of producing rare ketoses from polyols was isolated from soil and identified as Bacillus pallidus Y25. We have employed this isolated strain for the production of l-xylulose, a rare ketopentose, from xylitol by a resting cell reaction at 50°C. After optimization of culture conditions and reaction states, l-xylulose was produced at up to 85% yield when 2% xylitol was utilized. The key enzyme responsible for the interconversion of xylitol and l-xylulose was purified to homogeneity and identified as NAD-dependent xylitol dehydrogenase (XDH-Y25), with a molecular mass of 28kDa as determined by SDS-PAGE. XDH-Y25 is most active in glycine–NaOH buffer (pH 10) at 40°C and its substrate specificity is restricted to d-threitol, xylitol and d-iditol. This suggested that the enzyme is specific for polyols that have a hydroxyl group at the C-2 and C-3 positions in the l- and d-sides, respectively, in the Fischer projection. N-terminal amino acid sequencing of XDH-Y25 revealed low homology to any known dehydrogenases. To our knowledge, this is the first report on the characterization of xylitol dehydrogenase from a Bacillus species. [Copyright &y& Elsevier]

Abstract: l-Rhamnose isomerase (l-RhI) from Pseudomonas stutzeri LL172 can convert d-psicose to d-allose. Partially purified recombinant l-RhI from Escherichia coli was immobilized on BCW-2510 Chitopearl beads and utilized to produce d-allose. Total 20,000 units of immobilized enzyme converted d-psicose to d-allose without remarkable decrease in the enzyme activity over 17 days. When 50% d-psicose (w/w) was applied to a column with a flow rate of 0.8ml/min at 42°C, approximately 30% d-psicose was isomerized to d-allose for 17 days. However, by reducing the flow rate to 0.4ml/min after 17 days, d-allose was transformed at the same rate for 13 days. The total of 27l reaction mixture was separated by Simulated-Moving-Bed Chromatograph system. Approximately 2.2l/d of 50% (w/w) reaction mixture was separated continuously. After separation, d-allose and d-psicose fractions were 3l of approximately 10% (w/w) with 95% purity and 10l of approximately 8% (w/w) with 95% purity per day, respectively. The separated d-allose solution was concentrated up to about 50% and crystallized gradually by being kept at room temperature. Crystals of d-allose were separated from the syrup by filtration and 1.65kg crystals of 100% purity were obtained. The d-allose crystal yield from the d-psicose substrate was approximately 10%. [Copyright &y& Elsevier]

Escherichia coli strain JM 109 harboring 6× His-tag l-rhamnose isomerase (l-RhI) from Pseudomonas stutzeri allowed a 20-fold increase in the volumetric yield of soluble enzyme compared to the value for the intrinsic yield. Detailed studies on the substrate specificity of the purified His-tagged protein revealed that it catalyzed previously unknown common and rare aldo/ketotetrose, aldo/ketopentose, and aldo/ketohexose substrates in both d- and l-forms, for instance, erythrose, threose, xylose, lyxose, ribose, glucose, mannose, galactose, altrose, tagatose, sorbose, psicose, and fructose. Using a high enzyme–substrate ratio in extended reactions, the enzyme-catalyzed interconversion reactions from which two different products from one substrate were formed: l-lyxose, l-glucose, l-tagatose and d-allose were isomerized to l-xylulose and l-xylose, l-fructose and l-mannose, l-galactose and l-talose, and d-psicose and d-altrose, in that order. Kinetic studies, however, showed that l-rhamnose with Km and Vmax values of 11 mM and 240 U/mg, respectively, was the most preferred substrate, followed by l-mannose, l-lyxose, d-ribose, and d-allose. Based on the observed catalytic mode of action, these new findings reflected a hitherto undetected interrelation between l-RhI and d-xylose isomerase (d-XI). [Copyright &y& Elsevier]

• ABE solventogenesis with reducing agents and controlled feeding regimen. • L-cysteine and DTT fed-batches achieved solvent yield of 0.38 and 0.37 g/g. • 24.33 and 22.98 g/L of ABE produced by L-cysteine and DTT fed-batches. • Enhanced solventogenesis led to higher ATP levels in DTT and L-cysteine batches. • Histidine secretion is important in Clostridial acid stress. Acetone-butanol-ethanol (ABE) fermentation process is a promising bioenergy option amid rising concerns over the environmental impact of fossil fuel usage. However, the commercialization of the ABE process has been marred by challenges of low product yield and titer, thereby non-competitive process economics. Here, we coupled cost competitive reducing agents with a controlled feeding strategy to improve both product titer and yield. Reducing agents promote cofactor dependent butanol production, while fed-batch operation enhances glucose consumption, final ABE titer, and partly mitigates product toxicity. The effects of ascorbic acid, L-cysteine, and dithiothreitol (DTT) on ABE fed-batch production using Clostridium acetobutylicum was investigated in current study. NADH, ATP, extracellular amino acid secretion, and NADH-dependent butanol dehydrogenase (BDH) assays were performed to study the metabolic modifications triggered by reducing agents. Incidentally, L-cysteine and DTT improved ABE solvent titer by 2-fold, producing 24.33 and 22.98 g/L ABE with solvent yields of 0.38 and 0.37 g/g, respectively. Elevated NADH, BDH, and ATP levels in fermentation broth reflected in enhanced ABE titer and yield. Furthermore, histidine secretion emerged as an important factor in Clostridial acid stress tolerance in this study. The results demonstrate that addition of reducing agents in fed-batch ABE fermentation operation enables efficient utilization of glucose with significant improvement in solvent production. [ABSTRACT FROM AUTHOR]