Forgot your password?
New user?
New Window Opens on the Secret Life of Microbes: Scientists Develop First Microbial Profiles of Ecosystems
CAS announces the release of SciFinder Scholar for Mac OS X
Press Releases
Press Releases
| Check out our New Publishers' Select for Free Articles |
Applied Biochemistry and Biotechnology: Part A: Enzyme Engineering and Biotechnology (v.153, #1-3)
Session 1: Advances in Bioenergy Feedstocks and Plant Science
by C. Neal Stewart Jr.; Timothy Tschaplinski (pp. 1-3).
The Effect of Drying Temperature on the Composition of Biomass by Tracy P. Houghton; Daniel M. Stevens; Peter A. Pryfogle; Christopher T. Wright; Corey W. Radtke (pp. 4-10).
The compositional quality of different lignocellulosic feedstocks influences their performance and potential demand at a biorefinery. Many analytical protocols for determining the composition or performance characteristics of biomass involve a drying step, where the drying temperature can vary depending on the specific protocol. To get reliable data, it is important to determine the correct drying temperature to vaporize the water without negatively impacting the compositional quality of the biomass. A comparison of drying temperatures between 45 °C and 100 °C was performed using wheat straw and corn stover. Near-infrared (NIR) spectra were taken of the dried samples and compared using principal component analysis (PCA). Carbohydrates were analyzed using quantitative saccharification to determine sugar degradation. Analysis of variance was used to determine if there was a significant difference between drying at different temperatures. PCA showed an obvious separation in samples dried at different temperatures due to sample water content. However, quantitative saccharification data shows, within a 95% confidence interval, that there is no significant difference in sugar content for drying temperatures up to 100 °C for wheat straw and corn stover.
Keywords: NIR; Biomass; Drying; PCA
Sessions 2 and 7: Advances in Microbial Science and Technology
by Joy Doran-Peterson; David Hogsett; Badal C. Saha; Mark H. Emptage (pp. 11-12).
Butanol Tolerance in a Selection of Microorganisms by Eric P. Knoshaug; Min Zhang (pp. 13-20).
Butanol tolerance is a critical factor affecting the ability of microorganisms to generate economically viable quantities of butanol. Current Clostridium strains are unable to tolerate greater than 2% 1-butanol thus membrane or gas stripping technologies to actively remove butanol during fermentation are advantageous. To evaluate the potential of alternative hosts for butanol production, we screened 24 different microorganisms for their tolerance to butanol. We found that in general, a barrier to growth exists between 1% and 2% butanol and few microorganisms can tolerate 2% butanol. Strains of Escherichia coli, Zymomonas mobilis, and non-Saccharomyces yeasts were unable to surmount the 2% butanol growth barrier. Several strains of Saccharomyces cerevisiae exhibit limited growth in 2% butanol, while two strains of Lactobacillus were able to tolerate and grow in up to 3% butanol.
Keywords: Butanol; Tolerance; BioScreenC
Engineering Escherichia coli for Fermentative Dihydrogen Production: Potential Role of NADH-Ferredoxin Oxidoreductase from the Hydrogenosome of Anaerobic Protozoa by Phi Minh Do; Alexander Angerhofer; Ivan Hrdy; Lucie Bardonova; Lonnie O. Ingram; K. T. Shanmugam (pp. 21-33).
Trichomonas vaginalis generates reduced ferredoxin within a unique subcellular organelle, hydrogenosome that is used as a reductant for H2 production. Pyruvate ferredoxin oxidoreductase and NADH dehydrogenase (NADH-DH) are the two enzymes catalyzing the production of reduced ferredoxin. The genes encoding the two subunits of NADH-DH were cloned and expressed in Escherichia coli. Kinetic properties of the recombinant heterodimer were similar to that of the native enzyme from the hydrogenosome. The recombinant holoenzyme contained 2.15 non-heme iron and 1.95 acid-labile sulfur atoms per heterodimer. The EPR spectrum of the dithionite-reduced protein revealed a [2Fe–2S] cluster with a rhombic symmetry of g xyz = 1.917, 1.951, and 2.009 corresponding to cluster N1a of the respiratory complex I. Based on the Fe content, absorption spectrum, and the EPR spectrum of the purified small subunit, the [2Fe–2S] cluster was located in the small subunit of the holoenzyme. This recombinant NADH-DH oxidized NADH and reduced low redox potential electron carriers, such as viologen dyes as well as Clostridium ferredoxin that can couple to hydrogenase for H2 production from NADH. These results show that this unique hydrogenosome NADH dehydrogenase with a critical role in H2 evolution in the hydrogenosome can be produced with near-native properties in E. coli for metabolic engineering of the bacterium towards developing a dark fermentation process for conversion of biomass-derived sugars to H2 as an energy source.
Keywords: Trichomonas; Hydrogenosome; NADH dehydrogenase; Fermentation; H2 production
Total Soluble Solids from Banana: Evaluation and Optimization of Extraction Parameters by Giovani B. M. Carvalho; Daniel P. Silva; Júlio C. Santos; Hélcio J. Izário Filho; António A. Vicente; José A. Teixeira; Maria das Graças A. Felipe; João B. Almeida e Silva (pp. 34-43).
Banana, an important component in the diet of the global population, is one of the most consumed fruits in the world. This fruit is also very favorable to industry processes (e.g., fermented beverages) due to its rich content on soluble solids and minerals, with low acidity. The main objective of this work was to evaluate the influence of factors such as banana weight and extraction time during a hot aqueous extraction process on the total soluble solids content of banana. The extract is to be used by the food and beverage industries. The experiments were performed with 105 mL of water, considering the moisture of the ripe banana (65%). Total sugar concentrations were obtained in a beer analyzer and the result expressed in degrees Plato (°P, which is the weight of the extract or the sugar equivalent in 100 g solution at 20 °C), aiming at facilitating the use of these results by the beverage industries. After previous studies of characterization of the fruit and of ripening performance, a 22 full-factorial star design was carried out, and a model was developed to describe the behavior of the dependent variable (total soluble solids) as a function of the factors (banana weight and extraction time), indicating as optimum conditions for extraction 38.5 g of banana at 39.7 min.
Keywords: Banana; Soluble sugars; Extraction process; Experimental design; Response surface
Effect of Nutrients on Fermentation of Pretreated Wheat Straw at very High Dry Matter Content by Saccharomyces cerevisiae by Henning Jørgensen (pp. 44-57).
Wheat straw hydrolysate produced by enzymatic hydrolysis of hydrothermal pretreated wheat straw at a very high solids concentration of 30% dry matter (w/w) was used for testing the effect of nutrients on their ability to improve fermentation performance of Saccharomyces cerevisiae. The nutrients tested were MgSO4 and nitrogen sources; (NH4)2SO4, urea, yeast extract, peptone and corn steep liquor. The fermentation was tested in a separate hydrolysis and fermentation process using a low amount of inoculum (0.33 g kg−1) and a non-adapted baker’s yeast strain. A factorial screening design revealed that yeast extract, peptone, corn steep liquor and MgSO4 were the most significant factors in obtaining a high fermentation rate, high ethanol yield and low glycerol formation. The highest volumetric ethanol productivity was 1.16 g kg−1 h−1 and with an ethanol yield close to maximum theoretical. The use of urea or (NH4)2SO4 separately, together or in combination with MgSO4 or vitamins did not improve fermentation rate and resulted in increased glycerol formation compared to the use of yeast extract. Yeast extract was the single best component in improving fermentation performance and a concentration of 3.5 g kg−1 resulted in high ethanol yield and a volumetric productivity of 0.6 g kg−1 h−1.
Keywords: Yeast extract; Cellulose; Pretreatment; Wheat straw; Enzymatic hydrolysis; SHF
Bioremediation of Marine Sediments Impacted by Petroleum by Aike C. da Silva; Fernando J. S. de Oliveira; Diogo S. Bernardes; Francisca P. de França (pp. 58-66).
The aim of this work was to optimize the bioremediation of crude oil-contaminated sand sediment through the biostimulation technique. The soil was obtained in the mid-tide zone of Guanabara Bay, Rio de Janeiro, Brazil and was artificially contaminated with crude oil at 14 g kg−1. Bioremediation optimization was performed using an experimental design and statistical analysis of the following factors: supplementation with commercial biosurfactant Jeneil® IBR 425 and commercial mineral NPK fertilizer. The response variable used was the biodegradation of the heavy oil fraction, HOF. The analysis of the studied factors and their interactions was executed using contour plots, Pareto diagram and ANOVA table. Experimental design results indicated that the supplementation with fertilizer at 100:25:25 C/N/P ratio and biosurfactant at 2 g kg−1 yielded biodegradation of HOF at about 30% during 30 days of process. Some experiments were carried out using the experimental design results, yielding 65% of biodegradation of HOF and 100% of n- alkanes between C15 and C30 during 60 process days. Intrinsic biodegradation test was carried out, yielding 85% of biodegradation of n-alkanes between C15 and C30 during 30 days of process.
Keywords: Marine sediments; Petroleum; Bioremediation; Biostimulation; Intrinsic bioremediation
Study on Mass Transfer of Isopropylbenzene and Oxygen in a Two-Phase Partitioning Bioreactor in the Presence of Silicone Oil by Jean-Marc Aldric; Jean-Paul Lecomte; Philippe Thonart (pp. 67-79).
A two-phase partitioning bioreactor to treat gas effluents polluted by volatile organic compound has been developed. In this work, both the mass transfer of isopropylbenzene (IPB) and oxygen have been considered in relation to their influence on the hydrodynamics of the reactor and the type of silicone oils used as a second phase. The synergistic effect of silicone oil and stirrer speed on the global oxygen mass transfer coefficient (K L a) and gas holdup (up to 12%) have been investigated. The addition of 10% of low viscosity silicone oil (10 cSt) in the reactor does not significantly affect the oxygen transfer rate. The very high solubility of IPB in the silicone oil leads to an enhancement of driving force term, especially for high fraction of silicone oil. However, it does not seem useful to exceed a volume fraction of 10% since K L a IPB decreases sharply at higher proportions of silicone oil. K L a IPB and K L a O2 evolve in the same way with the proportion of silicone oil. These results confirm the potentialities of our bioreactor to improve both the oxygen and pollutant gas transfer in the field of the treatment of gaseous pollutants, even for highly concentrated effluents.
Keywords: VOC; Two-phase partitioning bioreactor; Mass transfer enhancement; Hydrodynamics; Silicone oil
Sessions 3 and 8: Pretreatment and Biomass Recalcitrance: Fundamentals and Progress
by Y.-H. Percival Zhang; Eric Berson; Simo Sarkanen; Bruce E. Dale (pp. 80-83).
Wheat Straw Autohydrolysis: Process Optimization and Products Characterization by Florbela Carvalheiro; Talita Silva-Fernandes; Luís C. Duarte; Francisco M. Gírio (pp. 84-93).
Wheat straw was subjected to autohydrolysis treatments in order to selectively hydrolyze the hemicellulose fraction. The effects of temperature (150–240°C) and non-isothermal reaction time on the composition of both liquid and solid phases were evaluated and interpreted using the severity factor (log R 0). The operational conditions leading to the maximum recovery of hemicellulose-derived sugars were established for log R 0 = 3.96 and correspond to 64% of the original (arabino)xylan with 80% of sugars as xylooligosaccharides. Under these conditions, a solubilization of 58% xylan, 83% arabinan, and 98% acetyl groups occurred. Glucan was mainly retained in the solid phase (maximum solubilization 16%), which enables an enrichment of the solid phase to contain up to 61% glucan. Delignification was not extensive, being utmost 15%. The yields of soluble products, including sugars, acetic acid, and degradation compounds, such as, furfural, 5-hydroxymethylfurfural furfural obtained suggest the fitness of liquid stream for fermentation purposes or to obtain xylooligosaccharides with potential applications in food, pharmaceutical, and cosmetic industries.
Keywords: Autohydrolysis; Pre-treatment; Wheat straw; Xylooligosaccharides
Protein Extraction and Enzymatic Hydrolysis of Ammonia-Treated Cassava Leaves (Manihot esculenta Crantz) by Lauris Urribarrí; David Chacón; Orlaidy González; Alexis Ferrer (pp. 94-102).
In the present work, cassava leaves were treated with 0.5 kg ammonia/kg dry matter at 78 °C and 30% moisture content in a 2-kg reactor. Protein extraction was carried out with a calcium hydroxide solution (pH 10) for 30 min at several temperatures (30 °C, 45 °C, 60 °C, 75 °C, and 90 °C) and solid/liquid ratios (1:10 and 1:15) in a thermostatized bath. Soluble protein content of the extracts was determined by Lowry’s method. Dry substrate concentrations of 5%, 7.5%, and 10% and enzyme doses of 2 and 5 IU/g dry matter were used for the enzymatic hydrolysis in an orbital incubator at 50 °C and 100 rpm. Both cellulase and xylanase were used. Reducing sugars produced were determined with the dinitrosalicylic acid method. The highest protein extraction yield for the ammonia-treated leaves was 29.10%, which was 50% higher than with the untreated leaves (20%), and was obtained at 90 °C with a 1:10 solid/liquid ratio. The concentrate had a protein content of 36.35% and the amino acid profile was suitable for swine and poultry. The highest sugar yield was 54.72% with respect to theoretical and was obtained with 5% solids and an enzyme dose of 5 IU/g dry matter. This yield was 3.4 times higher than the yield of the untreated leaves (16.13%). These results indicate that cassava leaves have a great potential for animal feeding and ethanol production. Both protein extraction and sugar yields may be enhanced by optimizing the ammonia treatment.
Keywords: Cassava leaves; Leaf protein; Sugars; Ammonia treatment
Enzymatic Saccharification and Viscosity of Sawdust Slurries Following Ultrasonic Particle Size Reduction by Samin Rezania; Zhuoliang Ye; R. Eric Berson (pp. 103-115).
Results in a previous study showed up to a 55% increase in saccharification rates when the initial particle size range decreased from 590 < x < 850 μm down to 33 < x < 75 μm. The smaller particle sizes also lowered the viscosity of the slurry 50-fold (for an equivalent initial solids concentration). In this study, ultrasonic irradiation was employed to further reduce the particle size of sawdust slurries below the ranges in the previous study in an attempt to further increase enzymatic saccharification rates and lower the slurry viscosity. Average particle sizes were reduced to less than 1 μm under the conditions tested. Surprisingly, the amount and rates of sugar released in this study with the ~1 μm particles is comparable (maximum glucose release of 30%) to, but no better than that seen for particle sizes in the range of 33 ≤ x ≤ 75 μm (maximum glucose release of 31%). Also surprisingly, the viscosity increased as the average particle sizes in the slurries decreased, which is opposite to the trend in the previous study. For example, there was an approximately threefold increase in the viscosity between unsonicated samples with a range of 10 ≤ x ≤ 75 μm and sonicated samples with a range of 0.05 ≤ x ≤ 12 μm. This is attributed to the variations in surface characteristics of the particles which were characterized here using X-ray diffraction profiles and SEM pictures.
Keywords: Biomass; Sawdust; Enzymatic hydrolysis; Saccharification; Particle size; Viscosity; Ultrasonic
Dilute Acid Hydrolysis of Wheat Straw Oligosaccharides by Luís C. Duarte; Talita Silva-Fernandes; Florbela Carvalheiro; Francisco M. Gírio (pp. 116-126).
The dilute acid posthydrolysis of wheat straw hemicellulosic oligosaccharides obtained by autohydrolysis was evaluated. An empirical model was used to describe the effect of catalyst concentration (sulfuric acid, 0.1–4% w/w) and reaction time (0–60 min) based on data from a Doehlert experimental design. Catalyst concentration is the main variable influencing posthydrolysis performance, as both its linear and quadratic coefficients are statistically significant for the majority of the studied variables, namely, the ones related to sugar and byproducts production. Reaction time influences xylose and furan derivatives concentrations but not phenolics or acetic acid content. Catalyst concentration and reaction time interact synergistically, minimizing sugar recovery and promoting furan derivatives production. Based on the proposed models, it was possible to delimit an operational range that enables to obtain high monosaccharides recovery together with a slight decrease in inhibitors content as compared to the standard acid hydrolysis treatment. Furthermore, this is achieved with up to 70% less acid spending or considerable savings on reaction time.
Keywords: Autohydrolysis; Dilute acid posthydrolysis; Experimental design; Hemicellulosic hydrolyzate; Wheat straw; Xylooligosaccharides
Acid Hydrolysis of Hemicellulose in Green Liquor Pre-Pulping Extract of Mixed Northern Hardwoods by Byung-Hwan Um; G. Peter van Walsum (pp. 127-138).
Forest biomass is a promising resource for future biofuels and bioproducts. Pre-pulping extraction of hemicellulose by alkaline (Green Liquor) pretreatment produces a neutral-pH extract containing hemicellulose-derived oligomers. A near-term option for use of this extract is to hydrolyze the oligomers to fermentable monomer sugars. Chips of mixed northern hardwoods were cooked in a rocking digester at 160 °C for 110 min in Green Liquor at a concentration of 3% Na2O equivalent salts on dry wood. The mass of wood extracted into the Green Liquor extract was approximately 11.4% of the debarked wood mass, which resulted in a dilute solution of oligomeric hemicelluloses sugars. The concentration of the extract was increased through partial evaporation prior to hydrolysis. Dilute sulfuric acid hydrolysis was applied at conditions ranging from 100 to 160 °C, 2% to 6% (w/v) H2SO4, and 2- to 258-min residence time. The maximum fermentable sugar concentration achieved from evaporated extract was 10.7 g/L, representing 90.7% of the maximum possible yield. Application of the biomass pretreatment severity function to the hydrolysis results proved to offer a relatively poor prediction of temperature and reaction time interaction. The combined severity function, which incorporates reaction time, temperature, and acid concentration, did prove to provide a useful means of trading off the combined effects of these three variables on total sugar yields.
Keywords: Northeast mixed hardwood; Acid hydrolysis; Acetic acid; Green Liquor extraction
Lime Pretreatment of Sugarcane Bagasse for Bioethanol Production by Sarita C. Rabelo; Rubens Maciel Filho; Aline Carvalho Costa (pp. 139-150).
The pretreatment of sugarcane bagasse with lime (calcium hydroxide) is evaluated. The effect of lime pretreatment on digestibility was studied through analyses using central composite design (response surface), considering pretreatment time, temperature, and lime loading as factors. The responses evaluated were the yield of glucose from pretreated bagasse after enzymatic hydrolysis. Experiments were performed using the bagasse as it comes from an alcohol/sugar factory (non-screened bagasse) and bagasse in the size range from 0.248 to 1.397 mm (screened bagasse) (12-60 mesh). It was observed that the particle size presented influence in the release of fermentable sugars after enzymatic hydrolysis using low loading of cellulase and β-glucosidase (3.5 FPU/g dry pretreated biomass and 1.0 IU/g dry pretreated biomass, respectively).
Keywords: Lignocellulose materials; Sugarcane bagasse; Pretreatment; Lime; Enzymatic hydrolysis; Statistical analysis
Sweet Sorghum as Feedstock for Ethanol Production: Enzymatic Hydrolysis of Steam-Pretreated Bagasse by Bálint Sipos; Jutka Réczey; Zsolt Somorai; Zsófia Kádár; Dóra Dienes; Kati Réczey (pp. 151-162).
Sweet sorghum is an attractive feedstock for ethanol production. The juice extracted from the fresh stem is composed of sucrose, glucose, and fructose and can therefore be readily fermented to alcohol. The solid fraction left behind, the so-called bagasse, is a lignocellulosic residue which can also be processed to ethanol. The objective of our work was to test sweet sorghum, the whole crop, as a potential raw material of ethanol production, i.e., both the extracted sugar juice and the residual bagasse were tested. The juice was investigated at different harvesting dates for sugar content. Fermentability of juices extracted from the stem with and without leaves was compared. Sweet sorghum bagasse was steam-pretreated using various pretreatment conditions (temperatures and residence times). Efficiency of pretreatments was characterized by the degree of cellulose hydrolysis of the whole pretreated slurry and the separated fiber fraction. Two settings of the studied conditions (190 °C, 10 min and 200 °C, 5 min) were found to be efficient to reach conversion of 85–90%.
Keywords: Sweet sorghum; Ethanol fermentation; Lignocellulose; Steam pretreatment; Enzymatic hydrolysis
Biotechnological Production of Xylitol: Enhancement of Monosaccharide Production by Post-Hydrolysis of Dilute Acid Sugarcane Hydrolysate by Boutros Fouad Sarrouh; Ricardo de Freitas Branco; Silvio Silvério da Silva (pp. 163-170).
Dilute-acid hydrolysis pretreatment of sugarcane bagasse resulted in release of 48% (18.4 g/L) of the xylan in the hemicellulose fraction into the hydrolysate as monomeric xylose. In order to enhance the recuperation of this monomer, a post-hydrolysis stage consisted of thermal treatment was carried out. This treatment resulted in an increase in xylose release of 62% (23.5 g/L) of the hemicellulose fraction. Original and post-hydrolysates were concentrated to the same levels of monomeric xylose in the fermentor feed. During the fermentation process, cellular growth was observed to be higher in the post-hydrolysate (3.5 g/L, Y x/s = 0.075 g cells/g xylose) than in the original hydrolysate (2.9 g/L, Y x/s = 0.068 g cells/g xylose). The post-treated hydrolysate required less concentration of sugars resulting in a lower concentration of fermentation inhibitors, which were formed primarily in the dilute acid hydrolysis step. Post-hydrolysis step led to a high xylose–xylitol conversion efficiency of 76% (0.7 g xylitol/g xylose) and volumetric productivity of 0.68 g xylitol/L h when compared to 71% (0.65 g xylitol/g xylose and productivity of 0.61 g xylitol/L h) for the original hemicellulosic hydrolysate.
Keywords: Dilute acid hydrolysis; Post-hydrolysis; Xylose monomers; Inhibitors; Xylitol
Pretreatment and Fractionation of Corn Stover by Soaking In Ethanol and Aqueous Ammonia by Tae Hyun Kim; Nhuan P. Nghiem; Kevin B. Hicks (pp. 171-179).
A new process for pretreatment of lignocellulosic biomass, designated the soaking in ethanol and aqueous ammonia (SEAA) process, was developed to improve hemicellulose preservation in solid form. In the SEAA process, an aqueous ammonia solution containing ethanol is used. Corn stover was treated with 15 wt.% ammonia at 1:9 solid–liquid ratio (by weight) at 60 °C for 24 h with ethanol added at 1, 5, 20, and 49 wt.% (balance was water). The extents by which xylan was solubilized with no ethanol and with ethanol added at 1, 5, 20, and 49 wt.% of the total liquid were 17.2%, 16.7%, 14.5%, 10.4%, and 6.3% of the original xylan, respectively. Thus, at the highest ethanol concentration used the loss of hemicellulose to the liquid phase was reduced by 63%. The digestibility of glucan and xylan in the pretreated corn stover samples by cellulase was not affected by ethanol addition of up to 20 wt.%. The enzymatic digestibility of the corn stover treated with 49 wt.% ethanol added was lower than the digestibility of the sample treated with no ethanol addition. Thus, based on these results, 20 wt.% was found to be the optimum ethanol concentration for use in the SEAA process for pretreatment of corn stover.
Keywords: Lignocellulosic biomass pretreatment; Soaking in ethanol and aqueous Ammonia; Hemicellulose preservation; Hemicellulose recovery; Ethanol precipitation