Showing papers in "Applied Biochemistry and Biotechnology in 1991"
TL;DR: The Ammonia Freeze Explosion (AFEX) process treats lignocellulose with high-pressure liquid ammonia, and then explosively releases the pressure as discussed by the authors, and the combined chemical effect and physical effect (increased accessible surface area) dramatically increase lignosulose susceptibility to enzymatic attack.
Abstract: The Ammonia Freeze Explosion (AFEX) process treats lignocellulose with high-pressure liquid ammonia, and then explosively releases the pressure. The combined chemical effect (cellulose decrystallization) and physical effect (increased accessible surface area) dramatically increase lignocellulose susceptibility to enzymatic attack. There are many adjustable parameters in the AFEX process: ammonia loading, water loading, temperature, time, blowdown pressure, and number of treatments. The effect of these parameters on enzymatic susceptibility was explored for three materials: Coastal bermudagrass, bagasse, and newspaper. Nearly quantitative sugar yields were demonstrated for Coastal bermudagrass and bagasse, using a very low enzyme loading (5 IU/g). Newspaper proved to be much more resistant to enzymatic hydrolysis.
253 citations
TL;DR: The interactive effects of ammonia and lactate were determined in a matrix experiment and at lactate and ammonia (1-4 mM), the growth inhibitory effects of the two components were synergistic, however, at low concentrations of lactate (< 12 mM) the toxic effect of ammonia was reduced.
Abstract: Eight independent cell lines accumulated ammonia in culture to concentrations between 1.3 and 2.9 mM. The growth inhibition of such concentrations of ammonium chloride when added to culture medium was variable. The cell lines tested could be divided into 3 groups depending on their growth response to 2 mM added NH4CI. In the first group (293, HDF, Vero, and PQXB1/2) little ( 75%) compared to controls. The growth inhibitory effect of added lactate up to 20 mM was negligible (<10%) for 3 cell lines, although one cell line (PQXB1/2) showed greater sensitivity.
247 citations
TL;DR: In this article, the effects of physicochemical and structural parameters of cellulose on the rate and degree of its enzymatic hydrolysis were tested with cellulosic materials from various sources.
Abstract: Effects of major physicochemical and structural parameters of cellulose on the rate and degree of its enzymatic hydrolysis were tested with cellulosic materials from various sources Some different pretreatments were: mechanical (milling), physical (X-ray irradiation), and chemical (cadoxen, H3PO4, H2SO4, NaOH, Fe2+/H2O2) The average size of cellulose particles and its degree of polymerization had little effect on the efficiency of enzymatic hydrolysis For samples of pure cellulose (cotton linter, microcrystalline cellulose, α-cellulose), increase in the specific surface area accessible to protein molecules and decrease in the crystallinity index accelerated the enzymatic hydrolysis (the correlation coefficients were 089 and 092, respectively) In the case of lignocellulose (bagasse), a quantitative linear relationship only between specific surface area and reactivity was observed
217 citations
TL;DR: In this article, three hardwoods (silver maple, sycamore, and black locust) and two corn residues (cobs and stover) were chosen and subjected to prehydrolysis with dilute sulfuric acid at 140 and 160 °C for reaction times ranging from 5 to 60 min.
Abstract: As a prerequisite for the enzymatic saccharification or simultaneous saccharification and fermentation process for ethanol synthesis, a dilute-acid pretreatment of the biomass has been shown to be a very effective first step in the yeast-catalyzed bioprocess. Three hardwoods (silver maple, sycamore, and black locust) and two corn residues (cobs and stover) were chosen and subjected to prehydrolysis with dilute sulfuric acid at 140 and 160 °C for reaction times ranging from 5 to 60 min. Although the hemicelluloses from all five samples could be completely hydrolyzed at both 140 and 160 °C, hydrolysis at 160 °C for the woods and stover produced a superior substrate for the cellulase enzyme from Trichoderma reesei, in which > 90% of the cellulose was hydrolyzed by the enzyme. Corn cobs produced an excellent substrate after only 5 min at 140°C. Small amounts of lignin and glucan were also solubilized by the acid in all samples.
198 citations
TL;DR: Algal strains from the Solar Energy Research Institute (Golden, CO) collection were selected as good fixers of CO2 when the level ofCO2 in the sparging gas was high, and these algae accumulated large amounts of crude lipids.
Abstract: Growth and lipid production of microalgae were investigated, with attention to the feasibility of making use of flue gas CO2 as a carbon source. The effect of a high CO2 level in artificial seawater differed from strain to strain. Three algal strains from the Solar Energy Research Institute (Golden, CO) collection were selected as good fixers of CO2 when the level of CO2 in the sparging gas was high. These algae also accumulated large amounts of crude lipids. SOX and NOX inhibited algal growth, but a green alga,Nannochloris sp. NANNO2 grew after a lag period, even when it received NO gas at the concentration of 300 ppm.
181 citations
TL;DR: A method for the modification of enzymes by MPEG carrying an amino acid or peptide as a spacer arm is described and tested with aliphatic or aromatic side chains amino acids to introduce proper reporter groups between the polymer and the protein.
Abstract: A method for the modification of enzymes by MPEG carrying an amino acid or peptide as a spacer arm is described and tested with aliphatic or aromatic side chains amino acids. The procedure involves MPEG activation byp-nitrophenylchloroformate for the amino acid or peptide coupling that is in turn activated for the protein binding.
119 citations
TL;DR: Yeast strains belonging to the groups Candida, Saccharomyces, andKluyveromyces were screened for their ability to grow and ferment glucose at temperatures ranging 32-45°C and were found to be the best ethanol producing organisms at the higher temperature tested.
Abstract: A total of 27 yeast strains belonging to the groups Candida, Saccharomyces, and Kluyveromyces were screened for their ability to grow and ferment glucose at temperatures ranging 32-45 degrees C. K. marxianus and K. fragilis were found to be the best ethanol producing organisms at the higher temperature tested and, so, were selected for subsequent simultaneous saccharification and fermentation (SSF) studies. SSF experiments were performed at 42 and 45 degrees C, utilizing Solkafloc (10%) as cellulose substrate and a cellulase loading of 15 FPU/g substrate. Best results were achieved at 42 degrees C with K. marxianus L. G. and K. fragilis L. G., both of which produced close to 38 g/L ethanol and 0.5 ethanol yield, in 78 h.
102 citations
TL;DR: It is concluded that as a result of its high surface-to-volume ratio (692/m) increased photoproduction of useful compounds may be achieved and such a system is generally applicable to all aspects of photobiotechnology.
Abstract: A photobioreactor was constructed in the form of a Perspex column 900 mm tall with an internal diameter of 70 mm. The reactor volume was 1.8 L and the light source consisted of a metal-halide lamp to reproduce sunlight. Light was distributed through the culture using a new type of optical fiber that diffuses light out through its surface, perpendicular to the fiber axis. A cluster of 661 light-diffusing optical fibers (LDOFs) pass from the light source through the reactor column (60-cm culture depth) and are connected to a mirror at the top of the reactor. This biosolar reactor has been used for the production of glutamate from CO2 by the marine cyanobacterium Synechococcus sp. NKBG040607. We present here details of the construction of the biosolar reactor and characterization of its properties. The effect of light intensity on glutamate production was measured. Carbon dioxide-to-glutamate conversion ratios were determined at different cell densities: the maximum conversion ratio (28%) was achieved at a cell density of 3x108 cells/mL. A comparison of glutamate production using the LDOF biosolar reactor described here with production by batch culture using free or immobilized cells showed that use of an optical-fiber biosolar reactor increased glutamate-production efficiency 6.75-fold. We conclude that as a result of its high surface-to-volume ratio (692/m) increased photoproduction of useful compounds may be achieved. Such a system is generally applicable to all aspects of photobiotechnology.
93 citations
TL;DR: Different strategies involving strain adaptation, and protein and genetic engineering adopted to overcome different obstacles in the fermentation of lignocellulose hydrolysate, are discussed.
Abstract: In the fermentation of lignocellulose hydrolysates to ethanol, two major problems are encountered: the fermentation of the pentose sugar xylose, and the presence of microbial inhibitors. Xylose can be directly fermented with yeasts, such as Pachysolen tannophilus, Candida shehatae, and Pichia stipis, or by isomerization of xylose to xylulose with the enzyme glucose (xylose) isomerase (XI; EC 5.3.1.5), and subsequent fermentation with bakers’ yeast, Saccharomyces cerevisiae. The direct fermentation requires low, carefully controlled oxygenation, as well as the removal of inhibitors. Also, the xylose-fermenting yeasts have a limited ethanol tolerance. The combined isomerization and fermentation with XI and S. cerevisiae gives yields and productivities comparable to those obtained in hexose fermentations without oxygenation and removal of inhibitors. However, the enzyme is not very stable in a lignocellulose hydrolysate, and S. cerevisiae has a poorly developed pentose phosphate shunt. Different strategies involving strain adaptation, and protein and genetic engineering adopted to overcome these different obstacles, are discussed.
91 citations
TL;DR: The immobilization of the phosphotriesterase onto nylon provides a practical method for the detoxification of organophosphate pesticides and methanol appears to be a competitive inhibitor for both forms of enzyme.
Abstract: A partially purified phophostriesterase was successfully immobilized onto nylon 6 and 66 membranes, nylon 11 powder, and nylon tubing. Up to 9000 U of enzyme activity was immobilized onto 2000 cm2 of a nylon 6 membrane where 1 U is the amount of enzyme necessary to catalyze the hydrolysis of 1.0 μmol of paraoxon/min at 25°C. The nylon 66 membrane-bound phosphotriesterase was characterized kinetically where the apparentK
m value for the immobilized enzyme was 0.35 mM. This is 5-6 times higher than that observed for the soluble enzyme. However, nylon immobilization limited the maximum rate of paraoxon hydrolysis to less than 10% of the value measured for the soluble enzyme. The addition of the cosolvent, methanol, resulted in an increase in the apparentK
m value for paraoxon hydrolysis but concentrations up to 40% had no negative effect on the catalytic effectiveness with the soluble or immobilized phosphotriesterase. Based on the kinetic analysis, methanol appears to be a competitive inhibitor for both forms of enzyme. The nylon powder immobilized enzyme was shown to be stable for at least 20 mo. The immobilization of the phosphotriesterase onto nylon provides a practical method for the detoxification of organophosphate pesticides.
83 citations
TL;DR: A NADPH/NADH-dependent xylose reductase gene was isolated from the xylOSE-assimilating yeast, Pichia stipitis, and DNA sequence analysis showed that the gene consists of 951 bp.
Abstract: A NADPH/NADH-dependent xylose reductase gene was isolated from the xylose-assimilating yeast,Pichia stipitis DNA sequence analysis showed that the gene consists of 951 bp The gene introduced inSaccharomyces cerevisiae was transcribed to mRNA, and a considerable amount of enzyme activity was observed constitutively, whereas transcription and translation inP stipitis were inducibleS cerevisiae carrying the xylose reductase gene could not, however, grow on xylose medium, and could not produce ethanol from xylose Since xylose uptake and accumulation of xylitol byS cerevisiae were observed, the conversion of xylitol to xylulose seemed to be limited
TL;DR: A better understanding of this feature of A. xylinum physiology may facilitate the preparation of bacterial cellulose pellicles, which are applied as a biotechnological tool in the treatment of skin burns and other dermal injuries.
Abstract: Caffeine and related xanthines were identified as potent stimulators for the bacterial cellulose production in A. xylinum. These compounds are present in several plants whose infusions are useful as culture-medium supplements for this acetobacterium. The proposed target for these native purine-like inhibitory substances is the novel diguanyl nucleotide phosphodiesterase(s) that participate(s) in the bacterial cellulogenic complex. A better understanding of this feature of A. xylinum physiology may facilitate the preparation of bacterial cellulose pellicles, which are applied as a biotechnological tool in the treatment of skin burns and other dermal injuries.
TL;DR: In this paper, an analysis of two pretreatment options, dilute sulfuric acid hydrolysis and sulfur dioxide impregnated steam explosion, for two feedstocks, wheat straw and aspen wood chips, was performed.
Abstract: Lignocellulosic biomass is one of the most plentiful and potentially cheapest feedstocks for ethanol production. The cellulose component can be broken down into glucose by enzymes and then converted to ethanol by yeast. However, hydrolysis of cellulose to glucose is difficult, and some form of pretreatment is necessary to increase the susceptibility of cellulose to enzymatic attack. An analysis has been completed of two pretreatment options, dilute sulfuric acid hydrolysis and sulfur dioxide impregnated steam explosion, for two feedstocks, wheat straw and aspen wood chips. Detailed process flow sheets and material and energy balances were used to generate equipment cost information. A technical and economic analysis compared the two feedstocks for each of the two pretreatments. For the same pretreatment, sugars produced from aspen wood hydrolysis were cheaper because of the higher carbohydrate content of aspen, whereas dilute acid pretreatment is favored over acid-catalyzed steam explosion.
TL;DR: Four commercial strains and two mutants of the yeast speciesYarrowia lipolytica were screened using batch fermentation and strain A-101-1.14 (induced with UV irradiation) was found to be the most suitable for citric acid production from glucose hydrol, a byproduct of glucose production from potato starch.
Abstract: Four commercial strains and two mutants of the yeast species Yarrowia lipolytica were screened using batch fermentation. Strain Y. lipolytica A-101-1.14 (induced with UV irradiation) was found to be the most suitable for citric acid production from glucose hydrol (39.9% glucose and 2.1% other sugars), a byproduct of glucose production from potato starch. The specific rate of total citric and isocitric acid production was 0.138 g/g.h, the yield on consumed glucose 0.93 g/g, and the productivity achieved was as high as 1.25 g/L.h. All of the tested yeast strains were able to utilize only the glucose from the glucose hydrol medium. Thus, some residual higher oligosaccharides remained in the process effluent.
TL;DR: The current state of understanding of the major groups of bacterial cellulase producers is reviewed and recently developed methods for the assessment of actual cellulase activity levels are addressed, reflective of the digester “hydrolytic potential,” using a series of detergent extractive procedures.
Abstract: Anaerobic digestion represents one of several commercially viable processes to convert woody biomass, agricultural wastes, and municipal solid wastes to methane gas, a useful energy source. This process occurs in the absence of oxygen, and is substantially less energy intensive than aerobic biological processes designed for disposal purposes. The anaerobic conversion process is a result of the synergistic effects of various microorganisms, which serve as a consortium. The rate-limiting step of this conversion process has been identified as the hydrolysis of cellulose, the major polymeric component of most biomass and waste feedstocks. Improvements in process economics therefore rely on improving the kinetic and physicochemical characteristics of cellulose degrading enzymes. The most thoroughly studied cellulase enzymes are produced by aerobic fungi, namelyTrichoderma reesei. However, the pH and temperature optima of fungal cellulases make them incompatible for use in anaerobic digestion systems, and the major populations of microorganisms involved in cellulase enzyme production under anaerobic digestion conditions are various bacterial producers. The current state of understanding of the major groups of bacterial cellulase producers is reviewed in this paper. Also addressed in this review are recently developed methods for the assessment of actual cellulase activity levels, reflective of the digester “hydrolytic potential,” using a series of detergent extractive procedures.
TL;DR: The fungi actively excreted large amounts of laccase in the medium, and at the same time the concentration of phenolics and other toxic compounds significantly decreased, as revealed by HPLC analysis and toxicity tests on standard cultures of human cell lines.
Abstract: Four species ofPleurotus were adapted to grow on olive milling wastewater, and in certain conditions produced high yield of fruit bodies. Some biochemical transformations were observed in the olive milling wastewater owing to the growth ofPleurotus. In particular, the fungi actively excreted large amounts of laccase in the medium, and at the same time the concentration of phenolics and other toxic compounds significantly decreased, as revealed by HPLC analysis and toxicity tests on standard cultures of human cell lines.
TL;DR: Thiolpeptides and thiolproteins, cellulose, crosslinked dextran, and polyacrylamide were shown to be very suitable as supports for solid-phase thiolsulfonates.
Abstract: A new method for the reversible immobilization of thiol bimolecules, e.g., thiolpeptides and thiolproteins, to beaded agarose and other solid phases is reported. The method consists of an activation and a coupling step. The activation is based on oxidation of disulfides (or thiol groups via disulfides) present in a solid phase by hydrogen peroxide at moderately acidic pH. This oxidation leads to disulfide oxides (thiolsulfinate groups of which the majority are further oxidized to thiolsulfonate). The thiolsulfonate groups react easily with thiol compounds, which become immobilized via disulfide bonds. The pH range for thiol coupling is wide (pH 5-8), but for most thiols the reaction seems to proceed faster at pH>7. The stability of the reactive group to hydrolysis, especially at neutral and weakly acidic pH, is very high. The activated gel, therefore, can be stored as a suspension at pH 5 for extended periods. The method has been used to reversibly immobilize glutathione, β-galactosidase, alcohol dehydrogenase, urease, and papain, all with exposed thiol groups as well as thiolated bovine serum albumin and sweet-potato β-amylase.
TL;DR: Hydrolysis of pure cellulose Avicel has been carried out, using Meicelase from Trichodertna viride, where the enzymatic activity of cellulase adsorbed on cellulose and its changes during the hydrolysis were investigated.
Abstract: Hydrolysis of pure cellulose Avicel has been carried out, using Meicelase fromTrichodertna viride, where the enzymatic activity of cellulase adsorbed on cellulose and its changes during the hydrolysis were investigated. A rapid drop of the hydrolysis rate during the reaction, that is always observed in enzymatic hydrolysis of cellulose, could be explained by a decline of specific activity of adsorbed enzyme, and it was implied that the decline results from a loss of synergistic action between endoglucanase and exoglucanase. An empirical equation expresses the change of hydrolysis rate during the reaction and also shows that the change of the hydrolysis rate is caused by the decline of the specific enzymatic activity of adsorbed enzyme.
TL;DR: A direct method based on amino acid analysis is proposed for the evaluation of monomethoxy(polyethylene glycol) covalently bound to protein, which exploits the use of MPEG, which was bounded with the unnatural amino acid nor-leucine (MPEG-Nle).
Abstract: To overcome the uncertainty of the colorimetric or fluorimetric method so far employed for the evaluation of monomethoxy(polyethylene glycol) (MPEG) covalently bound to protein, a direct method based on amino acid analysis is proposed. The method exploits the use of MPEG, which was bounded with the unnatural amino acid nor-leucine (MPEG-Nle). MPEG-Nle was activated at its carboxylic group to succinimidyl ester for the binding to the amino groups of protein.
TL;DR: In this paper, a method of protein quantitation that is usually applied to solutions, the bicinchoninic acid (BCA) assay, was used successfully to directly measure ng amounts of protein immobilized on the supports.
Abstract: Four different nonporous particulate materials, nylon, polystyrene, soda-lime silicate glass, and fused silica glass, have been evaluated for their appropriateness as immobilization supports for immunoglobulins. A method of protein quantitation that is usually applied to solutions, the bicinchoninic acid (BCA) assay, was used successfully to directly measure ng amounts of protein immobilized on the supports. Two proteins, a monoclonal antibody to theophylline and the biotin binding protein avidin, were studied. Radioactive theophylline and radioactive biotin were used to measure the activity of the immobilized protein. Ligand binding capacity per mm2 of support was measured as a function of amount of protein immobilized. By measuring both the amount of protein immobilized and its ligand binding capacity, we have determined that antitheophylline antibody adsorbed on polystyrene balls loses almost 90% of its binding activity after 65 h, although little protein is lost from the balls over this time. Avidin retains nearly full activity for biotin on polystyrene. The binding activity of biotinyl-antibody conjugate immobilized on avidin-adsorbed polystyrene is stable, even when stored for over 22 wk. Antibody covalently immobilized on soda-lime silicate glass beads retains its binding activity over long-term storage, although only 0.1 mol of 3H-theophylline bind per mol of immobilized antibody. Using fused silica glass particles as the solid support, the same antibody binds approx 0.6 mol of ligand per mol of immobilized antibody protein. The structural "softness" of the immunoglobulin requires that interaction with the surface be prevented in order to maintain activity.
TL;DR: Satisfactory results were attained when the biosensor was applied to the determination of BOD in brewery-plant and glutamate-plant wastewater and in a river, and the reproducibility was quite good.
Abstract: A microbial sensor consisting of immobilized yeast or bacterial cells and an oxygen electrode was developed for the estimation of biochemical oxygen demand (BOD). A flow-through system was used, and the response time was within 20 min. A linear relationship was observed between the relative current decrease and the BOD of the sample solution within the range of 1-45 mg/L. The storage lifetime was > 1 yr. The reproducibility was quite good, within 6% fsd at a concentration of 20 mg/L BOD. Satisfactory results were attained when the biosensor was applied to the determination of BOD in brewery-plant and glutamate-plant wastewater and in a river.
TL;DR: The studies to improve the production of glutaryl-7-ACA from cephalosporin C used whole cells of Trigonopsis variabilis, containing d-AAO, immobilized to magnetic iron oxide particles, and the presence of catalase coimmobilized with D-aaO and coupled to CNBr-activated Sepharose 4B improved the operation stability ofd- AAO.
Abstract: The studies to improve the production of glutaryl-7-ACA from cephalosporin C are described in this paper.
TL;DR: The cellulosome, the multienzyme complex of the cellulase system of Clostridium thermocellum, that mediates the solubilization of insoluble cellulose, is strongly inhibited by the major end product, cellobiose, but by combining a purified β-glucosidase from Aspergillus niger with the cellulosomes, accumulated cellobiOSE was hydrolyzed resulting in a dramatic enhancement of cellulose degradation.
Abstract: The cellulosome, the multienzyme complex of the cellulase system ofClostridium thermocellum, that mediates the solubilization of insoluble cellulose, is strongly inhibited by the major end product, cellobiose. By combining a purified β-glucosidase fromAspergillus niger with the cellulosome, accumulated cellobiose was hydrolyzed thereby resulting in a dramatic enhancement (up to 10-fold) of cellulose degradation. The observed enhancement was expressed both in the rate and degree of solubilization of microcrystalline cellulose, compared with that observed for the unsupplemented cellulosome. Near-complete conversion of cellulose to glucose could be obtained from dense substrate suspensions (up to at least 200 g/L).
TL;DR: Furfural was converted to several intermediates, including furfuryl alcohol, furoic acid, and acetic acid, before final conversion to methane and carbon dioxide under anaerobic conditions and resulted in 80% of the theoretically expected biogas.
Abstract: Furfural, a byproduct formed during the thermal/chemical pretreatment of hemicellulosic biomass, was degraded to methane and carbon dioxide under anaerobic conditions. The consortium of anaerobic microbes responsible for the degradation was enriched using small continuously stirred tank reactor (CSTR) systems with daily batch feeding of biomass pretreatment liquor and continuous addition of furfural. Although the continuous infusion of furfural was initially inhibitory to the anaerobic CSTR system, adaptation of the consortium occurred rapidly with high rates of furfural addition. Addition rates of 7.35 mg furfural/700-mL reactor/d resulted in biogas productions of 375%, of that produced in control CSTR systems, fed the biomass pretreatment liquor only. The anaerobic CSTR system fed high levels of furfural was stable, with a sludge pH of 7.1 and methane gas composition of 69%, compared to the control CSTR, which had a pH of 7.2 and 77% methane. CSTR systems in which furfural was continuously added resulted in 80% of the theoretically expected biogas. Intermediates in the anaerobic biodegradation of furfural were determined by spike additions in serum-bottle assays using the enriched consortium from the CSTR systems. Furfural was converted to several intermediates, including furfuryl alcohol, furoic acid, and acetic acid, before final conversion to methane and carbon dioxide.
TL;DR: In this paper, the two factors that most constrain the utilization of thermophilic bacteria for ethanol production, were investigated in continuous xylose-grown cultures ofClostridium thermosaccharolyticum.
Abstract: Ethanol yield and ethanol tolerance, the two factors that most constrain the utilization of thermophilic bacteria for ethanol production, were investigated in continuous xylose-grown cultures ofClostridium thermosaccharolyticum. Under xylose-limiting conditions, including varying dilution rates and feed concentrations, the ethanol selectivity (Se, mol/mol) relative to acetic acid, lactic acid, and propane diol remained relatively constant at about 2. Product addition and removal experiments indicate that mass action effects related to the concentrations of organic fermentation products play a relatively minor role in determining the ratios of products made. Of much greater apparent importance were as yet uncharacterized regulatory mechanisms that appear to be correlated with nonlimiting concentrations of the carbon and energy-source. Substrate-plentiful transients were found to accompany Se values > 11. Such transients provide a useful model system for the study of end product control, as well as a cultivation mode with considerable applied potential. No apparent ethanol inhibition was observed, as indicated by no decrease in the maximum rate of growth allowing complete substrate utilization (0.22 h-1) for endogenously-produced ethanol concentrations up to 11.4 g/L, and total endogenously-produced + exogenously-added ethanol concentrations up to 21.3 g/L. Higher concentrations of ethanol are tolerated atµ= 0.11 h-1, although the onset of inhibition was not characterized at this growth rate. Results suggest that the ethanol tolerance of C.thermosaccharolyticum grown in continuous culture may be greater than that typically observed previously for thermophiles grown in batch culture.
TL;DR: The cellulase complex of this strain was found to undergo catabolite repression in the presence of high concentrations of glucose, and ammonium sulfate, ammonium dihy-drogen orthophosphate, and corn-steep liquor were the best for the production of cellulolytic enzymes by A. niger.
Abstract: Aspergillus niger NCIM 1207 produces high levels of extracellular β-glucosidase and xylanase activities in submerged fermentation Among the nitrogen sources, ammonium sulfate, ammonium dihy-drogen orthophosphate, and corn-steep liquor were the best for the production of cellulolytic enzymes by A niger The optimum pH and temperature for cellulase production were 30-55 and 28°C, respectively The cellulase complex of this strain was found to undergo catabolite repression in the presence of high concentrations of glucose Glycerol at all concentrations caused catabolite repression of cellulase production The addition of glucose (up to 1% concentration) enhanced the production of cellulolytic enzymes, but a higher concentration of glucose effected the pronounced repression of enzymes Generally the growth on glucose- or glycerol-containing medium was accompanied by a sudden drop in the pH of the fermentation medium to 20
TL;DR: Results obtained for the conversion of synthesis gas to CH4 in 5- cm- and 16.5-cm-diameter trickle-bed reactors are compared and light requirements for R. rubrum are considered in bioreactor design.
Abstract: Carbon monoxide, H2, and CO2 in synthesis gas can be converted to CH4 by employing a triculture ofRhodospirillum rubrum, Methanosarcina barken, andMethanobacterium formicicum. Trickle-bed reactors have been found to be effective for this conversion because of their high mass-transfer coefficients. This paper compares results obtained for the conversion of synthesis gas to CH4 in 5-cm- and 16.5-cm-diameter trickle-bed reactors. Mass-transfer and scale-up parameters are defined, and light requirements forR. rubrum are considered in bioreactor design.
TL;DR: In this article, a pretreated poplar wood was carried out with initial concentrations of 1.26, 2.52, 5.04 mg proteinJmL of GC123Trichoderma reesei.
Abstract: The hydrolysis of pretreated poplar wood was carried out with initial concentrations of 1.26, 2.52, 5.04 mg proteinJmL of GC123Trichoderma reesei. cellulase and substrate concentrations of 2.5% wJv, 5% w/v, and 10% wJv at pH 4.8 and 40°C. The concentration of enzyme protein remaining in solution, the glucose concentration, and the total potential glucose concentrations were measured as a function of time during the hydrolysis. The enzyme rapidly adsorbed initially, reaching a maximum in about 30 min. About 55–75% of the cellulase returned to solution as the remaining cellulose was hydrolyzed. Dilution of the unhydrolyzed residue, largely lignin, did not cause additional desorption of the cellulase. The specific hydrolysis rate (i.e., the rateJamount of adsorbed enzyme) declined significantly with increased conversion, even when corrected for glucose inhibition. At a given initial substrate concentration, the specific rate was found to be largely independent of the total enzyme concentration. However, at a given fractional conversion, the specific rate was found to be reduced by increased substrate concentration.
TL;DR: Four promising woody crops were pretreated by dilute sulfuric acid and evaluated in the simultaneous saccharification and fermentation (SSF) process for ethanol production, and Saccharomyces cerevisiae alone achieved the highest ethanol yields and rates of hydrolysis at the higher enzyme loadings.
Abstract: Four promising woody crops (Populusmaximowiczii x nigra (NE388), P.trichocarpa x deltoides (Nll), P.tremuloides, and SweetgumLiquidambar styraciflua) were pretreated by dilute sulfuric acid and evaluated in the simultaneous saccharification and fermentation (SSF) process for ethanol production. The yeastSaccharomyces cerevisiae was used in the fermentations alone, and in mixed cultures with β -glucosidase producingBrettanomyces dausenii. Commercial Genencor 150L cellulase enyme was either employed alone or supplemented with β- glucosidase. All SSFs were run at 37 …C for 8 d and compared to saccharifications at 45…C under the same enzyme loadings.S. cerevisiae alone achieved the highest ethanol yields and rates of hydrolysis at the higher enzyme loadings, whereas the mixed culture performed better at the lower enzyme loadings without β -glucosidase supplementation. The best overall rates of fermentation (3 d) and final theoretical ethanol yields (86–90%) were achieved with P.maximowiczii x nigra (NE388) and SweetgumLiquidambar styraciflua, followed by P.tremuloides and P.trichocarpa xdeltoides (N1l) with slightly slower rates and lower yields. Although there were some differences in SSF performance, all these pretreated woody crops show promise as substrates for ethanol production.
TL;DR: The fermentation performance characteristics of recombinantEscherichia coli ATCC 11303 carrying the “PET plasmid” (pLOI297) with thelac operon controlling the expression of pyruvate decarboxylase(pdc) and alcohol dehydrogenase II(adhB) genes cloned fromZymomonas mobilis CP4 were assessed in batch and continuous processes with sugar mixtures designed to mimic process streams from lignocellul
Abstract: Efficient utilization of lignocellulosic feedstocks offers an opportunity to reduce the cost of producing fuel ethanol. The fermentation performance characteristics of recombinant Escherichia coli ATCC 11303 carrying the "PET plasmid" (pLOI297) with the lac operon controlling the expression of pyruvate decarboxylase (pdc) and alcohol dehydrogenase II (adhB) genes cloned from Zymomonas mobilis CP4 (Alterthum & Ingram, 1989) were assessed in batch and continuous processes with sugar mixtures designed to mimic process streams from lignocellulosic hydrolysis systems. Growth was pseudoexponential at a rate (generation time) of 1.28 h at pH 6.8 and 1.61 h at pH 6.0. The molar growth yields for glucose and xylose were 17.28 and 7.65 g DW cell/mol, respectively (at pH 6.3 and 30 degrees C), suggesting that the net yield of ATP from xylose metabolism is only 50% compared to glucose. In pH-stat batch fermentations (Luria broth with 6% sugar, pH 6.3), glucose was converted to ethanol 4-6 times faster than xylose, but the glucose conversion rate was much less than can be achieved with comparable cell densities of Zymomonas. Sugar-to-ethanol conversion efficiencies in nutrient-rich, complex LB medium were near theoretical at 98 and 88% for glucose and xylose, respectively. The yield was 10-20% less in a defined-mineral-salts medium. Acetate at a concentration of 0.1M (present in lignocellulosic hydrolysates from thermochemical processing) inhibited glucose utilization (about 50%) much more than xylose, and caused a decrease in product yield of about 30% for both sugars. With phosphate-buffered media (pH 7), glucose was a preferred substrate in mixtures with a ratio of hexose to pentose of 2.3 to 1. Xylose was consumed after glucose, and the product yield was less (0.37 g/g). Under steady-state conditions of continuous culture, the specific productivity ranged from 0.76-1.24 g EtOH/g cell/h, and the maximum volumetric productivity, 2.5 g EtOH/L/h, was achieved with a rich complex LB medium (glucose) at pH 6.0 (30 degrees C) and ethanol at 1.63% (v/v). Growth and fermentation were poor in a buffered-wood (aspen) "hemicellulose hydrolysate" containing 4% xylose and 0.1M acetate with added thiamine and mineral salts.