共查询到20条相似文献,搜索用时 15 毫秒
1.
Ali Mohagheghi Karel Grohmann Charles E. Wyman 《Applied biochemistry and biotechnology》1988,17(1-3):263-277
Cellulase production by the RUT-C30 mutant of the fungusTrichoderma reesei was studied on mixtures of xylose and cellulose. In mixed substrates, the lag phase of the growth cycle was shorter and reached
the maximum of total productivity in a shorter time compared to growth on the single substrate, cellulose. A diauxic pattern
of utilization of the two carbon sources was observed as well: Xylose was utilized first to support growth, followed by cellulose
to induce the cellulase enzyme production and provide an additional carbon source for cellular metabolism. Of the various
mixtures of xylose and cellulose used in batch enzyme production, a ratio of 30∶30 g/L of xylose to cellulose was optimal.
This mixture produced the highest maximal enzyme productivity of 122 IFPU/L h, and its total productivity reached a maximum
value of 55 IFPU/L h in less time than others. However, similar total productivities and higher enzyme titers were observed
for growth on cellulose alone. 相似文献
2.
Svihla C. Kurt Dronawat Sundeep N. Hanley Thomas R. 《Applied biochemistry and biotechnology》1995,(1):355-366
It can be difficult to obtain reliable rheological data for filamentous fermentation broths using conventional instruments.
One common approach is to measure the torque drawn by an impeller rotating in the suspension (1–7). Many previous workers have assumed that the applicable shear rate in such a device is related to the impeller speed by
a fluid-independent constant determined by calibration with Newtonian and non-Newtonian fluids (1–9). The rheology ofAspergillus niger broths have been characterized using the impeller viscometer approach. The changes in the broth rheology were measured, and
used to interpret the growth of biomass and the evolution of the microorganism morphology. 相似文献
3.
The gpdA-promoter-controlled exocellular production of glucose oxidase (GOD) by recombinant Aspergillus niger NRRL-3 (GOD3-18) during growth on glucose and nonglucose carbon sources was investigated. Screening of various carbon substrates
in shake-flask cultures revealed that exocellular GOD activities were not only obtained on glucose but also during growth
on mannose, fructose, and xylose. The performance of A. niger NRRL-3 (GOD3-18) using glucose, fructose, or xylose as carbon substrate was compared in more detail in bioreactor cultures.
These studies revealed that gpdA-promoter-controlled GOD synthesis was strictly coupled to cell growth. The gpdA-promoter was most active during growth on glucose. However, the unfavorable rapid GOD-catalyzed transformation of glucose
into gluconic acid, a carbon source not supporting further cell growth and GOD production, resulted in low biomass yields
and, therefore, reduced the advantageous properties of glucose. The total (endo- and exocellular) specific GOD activities
were lowest when growth occurred on fructose (only a third of the activity that was obtained on glucose), whereas utilization
of xylose resulted in total specific GOD activities nearly as high as reached during growth on glucose. Also, the portion
of GOD excreted into the culture fluid reached similar high levels (≅ 90%) by using either glucose or xylose as substrate,
whereas growth on fructose resulted in a more pelleted morphology with more than half the total GOD activity retained in the
fungal biomass. Finally, growth on xylose resulted in the highest biomass yield and, consequently, the highest total volumetric
GOD activity. These results show that xylose is the most favorable carbon substrate for gpdA-promoter-controlled production of exocellular GOD. 相似文献
4.
Baker John O. Adney William S. Nleves Rafael A. Thomas Steven R. Wilson David B. Himmel Michael E. 《Applied biochemistry and biotechnology》1994,(1):245-256
A new thermostable endoglucanase,Acidothermus cellulolyticus E1, and another bacterial endoglucanase, E5 fromThermomonospora fusca, each exhibit striking synergism with a fungal cellobiohydrolase (Trichoderma reesei CBH I) in the saccharification of microcrystalline cellulose. In neither case did the ratio of endoglucanase to exoglucanase
that demonstrated maximum synergism coincide exactly with the ratio that actually released the maximum quantity of soluble
sugar for a given total cellulase loading. The difference between the two ratios, after significant hydrolysis of the substrate,
was considerably larger in the case ofA. cellulolyticus E1. For both endoglucanase pairings with CBH I, the offset between the ratio for maximum synergism and the ratio for maximal
soluble sugar production was found to be a function of digestion time. 相似文献
5.
Probing the role of N-linked glycans in the stability and activity of fungal cellobiohydrolases by mutational analysis 总被引:1,自引:0,他引:1
William S. Adney Tina Jeoh Gregg T. Beckham Yat-Chen Chou John O. Baker William Michener Roman Brunecky Michael E. Himmel 《Cellulose (London, England)》2009,16(4):699-709
The filamentous fungi Trichoderma reesei and Penicillium funiculosum produce highly effective enzyme mixtures that degrade the cellulose and hemicellulose components of plant cell walls. Many
fungal species produce a glycoside hydrolase family 7 (Cel7A) cellobiohydrolase, a class of enzymes that catalytically process
from the reducing end of cellulose. A direct amino acid comparison of these two enzymes shows that they not only have high
amino acid homology, but also contain analogous N-linked glycosylation sites on the catalytic domain. We have previously shown (Jeoh et al. in Biotechnol Biofuels, 1:10,
2008) that expression of T. reesei cellobiohydrolase I in a commonly used industrial expression host, Aspergillus niger var. awamori, results in an increase in the amount of N-linked glycosylation of the enzyme, which negatively affects crystalline cellulose degradation activity as well as thermal
stability. This complementary study examines the significance of individual N-linked glycans on the surface of the catalytic domain of Cel7A cellobiohydrolases from T. reesei and P. funiculosum by genetically adding or removing N-linked glycosylation motifs using site directed mutagenesis. Modified enzymes, expressed in A. niger var. awamori, were tested for activity and thermal stability. It was concluded that N-linked glycans in peptide loops that form part of the active site tunnel have the greatest impact on both thermal stability
and enzymatic activity on crystalline cellulose for both the T. reesei and P. funiculosum Cel7A enzymes. Specifically, for the Cel7A T. reesei enzyme expressed in A. niger var. awamori, removal of the N384 glycosylation site yields a mutant with 70% greater activity after 120 h compared to the heterologously
expressed wild type T. reesei enzyme. In addition, similar activity improvements were found to be associated with the addition of a new glycosylation motif
at N194 in P. funiculosum. This mutant also exhibits 70% greater activity after 120 h compared to the wild type P. funiculosum enzyme expressed in A. niger var. awamori. Overall, this study demonstrates that “tuning” enzyme glycosylation for expression from heterologous expression hosts is
essential for generating engineered enzymes with optimal stability and activity. 相似文献
6.
M. Karsheva J. Hristov I. Penchev V. Lossev 《Applied biochemistry and biotechnology》1997,68(3):187-206
An experimental study of rheological behavior of three morphological types of fermentation broths in relation to process conditions
was carried out in industrial and pilot-plant bioreactors. Three industrially manufactured antibiotic broths were studied:
Cephalosporin C (fungal), tylosin (actinomycetic), and apramycin (proactinomycetic), in which the rheology may cause real
problems.
A viscometer with coaxial cylinders and six-blade impeller was used for rheological measurements. The shear rates range in
which both the instruments give similar results was determined.
During the experiments rheological and morphological behavior, pH, activity, biomass concentration, fats, glucose, and nitrogen
concentrations were studied.
All the broths studied exhibited nonNewtonian behavior, which could be described with Ostvald-de-Waele power-law model.
It was found that the rheological behavior of the broths during the process is closely related to biomass concentration and
morphological changes of mycelia, so that viscosity could be used as a parameter for process monitoring and regulation. A
set of experiments on oxygentransfer improvement in the case of the most viscous tylosin broths by water addition was also
done. 相似文献
7.
A cellulase production process was developed by growing the fungi Trichoderma reesei and Aspergillus phoenicis on dairy manure. T. reesei produced a high total cellulase titer (1.7 filter paper units [FPU]/mL, filter paper activity) in medium containing 10 g/L
of manure (dry basis [w/w]), 2 g/L KH2PO4, 2 mL/L of Tween-80, and 2mg/L of CoCl2. However, β-glucosidase activity in the T. reesei-enzyme system was very low. T. reesei was then cocultured with A. phoenicis to enhance the β-glucosidase level. The mixed culture resulted in a relatively high level of total cellulase (1.54 FPU/mL)
and β-glucosidase (0.64 IU/mL). The ratio of β-glucosidase activity to filter paper activity was 0.41, suitable for hydrolyzing
manure cellulose. The crude enzyme broth from the mixed culture was used for hydrolyzing the manure cellulose, and the produced
glucose was significantly (p<0.01) higher than levels obtained by using the commercial enzyme or the enzyme broth of the pure culture T. reesei. 相似文献
8.
Szengyel Zsolt Zacchi Guido Varga Amaranta Réczey Kati 《Applied biochemistry and biotechnology》2000,84(1-9):679-691
Various techniques are available for the conversion of lignocellulosics to fuel ethanol. During the last decade processes
based on enzymatic hydrolysis of cellulose have been investigated more extensively, showing good yield on both hardwood and
softwood. The cellulase production of a filamentous fungi, Trichoderma reesei Rut C30, was examined on carbon sources obtained after steam pretreatment of spruce. These materials were washed fibrous
steam-pretreated spruce (SPS), and hem icellulose hydrolysate. The hemicellulose hydrolysate contained, besides water-soluble
carbohydrates, lignin and sugar degradation products, which were formed during the pretreatment and proved to be inhibitory
to microorganisms. Experiments were performed in a 4-L laboratory fermentor. The hydrolytic capacity of the produced enzyme
solutions was compared with two commercially available enzyme preparations, Celluclast and logen Cellulase, on SPS, washed
SPS, and Solka Floc cellulose powder. There was no significant difference among the different enzymes produced by T. reesei Rut C30. However, the conversion of cellulose using these enzymes was higher than that obtained with logen or Celluclast
cellulases using steam-pretreated spruce as substrate. 相似文献
9.
A starter culture ofTrichoderma reesei (Rut-C30) prepared in a liquid fluidized bed reactor (LFBR) gave better growth and greater cellulase production in submerged
fermentation than a conventional shake flask inoculum. The LFBR starter was prepared by first coatingT. reesei spores to 0.25 mm size corncob (1.0x108g-1) in a medium containing 1.0% corncob, 0.5 gL-1 xylose and 0.1 gL-1 lactose in a balanced salt solution, then fluidizing the particles in the LFBR for 36 h to allow germination of the spores,
and covering the particles with an approx 30 μm thick biofilm. This biofilm that developed in constant adherence to the lignocellulosic
carrier, apparently became well adapted to grow rapidly on insoluble cellulose substrates (Solca Floc), and had the enzymes
of the cellulase complex induced for increased cellulase production.
The LFBR starter used in a stirred tank reactor (STR) gave 15 gL-1 biomass production and 6.5 IU mL-1 overall cellulase activity with a volumetric productivity of 64 IU L-1h-1 in a 5 d fermentation, compared with a 7 d shake flask inoculum that gave 11 gL-1 biomass and 3.2 IU mL-1 cellulase activity, with a volumetric productivity of 31IU L-1h-1. The LFBR starter culture retained its viability in dry storage for 6–9 mo. 相似文献
10.
Xin-Liang Li Bruce S. Dien Michael A. Cotta Y. Victor Wu Badal C. Saha 《Applied biochemistry and biotechnology》2005,121(1-3):321-334
Corn fiber is the fibrous by-product of wet-mill corn processing. It typically consists of about 20% starch, 14% cellulose,
and 30% hemicellulose in the form of arabinoxylan. Crude corn fiber (CCF) was fractionated into de-starched corn fiber (DSCF),
corn fiber with cellulose (CFC) enriched, and corn fiber arabinoxylan (CFAX), and these fractions were evaluated as substrates
for enzyme production by Trichoderma reesei. T. reesei QM9414 and Rut C-30 grew on CCF, DSCF, CFC, or CFAX and secreted a number of hydrolytic enzymes. The enzymes displayed synergism
with commercial cellulases for corn fiber hydrolysis.
Mention of trade names or commercial products in this article is solely for the purpose of providing specific information
and does not imply recommendation or endorsement by the U.S. Department of Agriculture. 相似文献
11.
Barley is an abundant crop in Europe, which makes its straw residues an interesting cellulose source for ethanol production.
Steam pretreatment of the straw followed by enzymatic hydrolysis converts the cellulose to fermentable sugars. Prior to pretreatment
the material is impregnated with a catalyst, for example, H2SO4, to enhance enzymatic digestibility of the pretreated straw. Different impregnation techniques can be applied. In this study,
soaking and spraying were investigated and compared at the same pretreatment condition in terms of overall yield of glucose
and xylose. The overall yield includes the soluble sugars in the liquid from pretreatment, including soluble oligomers, and
monomer sugars obtained in the enzymatic hydrolysis. The yields obtained differed for the impregnation techniques. Acid-soaked
barley straw gave the highest overall yield of glucose, regardless of impregnation time (10 or 30 min) or acid concentration
(0.2 or 1.0 wt%). For xylose, soaking gave the highest overall yield at 0.2 wt% H2SO4. An increase in acid concentration resulted in a decrease in xylose yield for both acid-soaked and acid-sprayed barley straw.
Optimization of the pretreatment conditions for acid-sprayed barley straw was performed to obtain yields using spraying that
were as high as those with soaking. For acid-sprayed barley straw the optimum pretreatment condition for glucose, 1.0 wt%
H2SO4 and 220°C for 5 min, gave an overall glucose yield of 92% of theoretical based on the composition of the raw material. Pretreatment
with 0.2wt% H2SO4 at 190°C for 5 min resulted in the highest overall xylose yield, 67% of theoretical based on the composition of the raw material. 相似文献
12.
Nóra Szijártó Zsolt Szengyel Gunnar Lidén Kati Réczey 《Applied biochemistry and biotechnology》2004,113(1-3):115-124
An economic process for the enzymatic hydrolysis of cellulose would allow utilization of cellulosic biomass for the production
of easily fermentable low-cost sugars. New and more efficient fermentation processes are emerging to convert this biologic
currency to a variety of commodity products with a special emphasis on fuel ethanol production. Since the cost of cellulase
production currently accounts for a large fraction of the estimated total production costs of bioethanol, a significantly
less expensive process for cellulase enzyme production is needed. It will most likely be desirable to obtain cellulase production
on different carbon sources—including both polymeric carbohydrates and monosaccharides. The relation between enzyme production
and growth profile of the microorganism is key for designing such processes. We conducted a careful characterization of growth
and cellulase production by the soft-rot fungus Trichoderma reesei. Glucosegrown cultures of T. reesei Rut-C30 were subjected to pulse additions of Solka-floc (delignified pine pulp), and the response was monitored in terms
of CO2 evolution and increased enzyme activity. There was an immediate and unexpectedly strong CO2 evolution at the point of Solka-floc addition. The time profiles of induction of cellulase activity, cellulose degradation,
and CO2 evolution are analyzed and discussed herein. 相似文献
13.
The production cost of cellulolytic enzymes is a major contributor to the high cost of ethanol production from lignocellulosics
using enzymatic hydrolysis. The aim of the present study was to investigate the cellulolytic enzyme production ofTrichoderma reesei Rut C 30, which is known as a good cellulase secreting micro-organism, using willow as the carbon source. The willow, which
is a fast-growing energy crop in Sweden, was impregnated with 1–4% SO2 and steam-pretreated for 5 min at 206°C. The pretreated willow was washed and the wash water, which contains several soluble
sugars from the hemicellulose, was supplemented with fibrous pretreated willow and used for enzyme production. In addition
to sugars, the liquid contains degradation products such as acetic acid, furfural, and 5-hydroxy-methylfurfural, which are
inhibitory for microorganisms. The results showed that 50% of the cellulose can be replaced with sugars from the wash water.
The highest enzyme activity, 1.79 FPU/mL and yield, 133 FPU/g carbohydrate, was obtained at pH 6.0 using 20 g/L carbon source
concentration. At lower pHs, a total lack of growth and enzyme production was observed, which probably could be explained
by furfural inhibition. 相似文献
14.
Mahesh S. Krishnan Nancy W. Y. Ho George T. Tsao 《Applied biochemistry and biotechnology》1999,78(1-3):373-388
Fermentation kinetics of ethanol production from glucose, xylose, and their mixtures using a recombinant Saccharomyces 1400 (pLNH33) are reported. Single-substrate kinetics indicate that the specific growth rate of the yeast and the specific
ethanol productivity on glucose as the substrate was greater than on xylose as a substrate. Ethanol yields from glucose and
xylose fermentation were typically 95 and 80% of the theoretical yield, respectively. The effect of ethanol inhibition is
more pronounced for xylose fermentation than for glucose fermentation. Studies on glucose-xylose mixtures indicate that the
recombinant yeast co-ferments glucose and xylose. Fermentation of a 52.8 g/L glucose and 56.3 g/L xylose mixture gave an ethanol
concentration of 47.9 g/L after 36 h. Based on a theoretical yield of 0.51 g ethanol/g sugars, the ethanol yield from this
experiment (for data up to 24 h) was calculated to be 0.46 g ethanol/g sugar or 90% of the theoretical yield. The specific
growth rate of the yeast on glucose-xylose mixtures was found to lie between the specific growth rate on glucose and the specific
growth rate on xylose. Kinetic studies were used to develop a fermentation model incorporating the effects of substrate inhibition,
product inhibition, and inoculum size. Good agreements were obtained between model predictions and experimental data from
batch fermentation of glucose, xylose, and their mixtures. 相似文献
15.
E. Sprong D. De Wet‐Roos M. P. Tonge R. D. Sanderson 《Journal of polymer science. Part A, Polymer chemistry》2003,41(2):223-235
Model alkali‐soluble rheology modifiers of different molar masses were synthesized by the reversible addition–fragmentation chain‐transfer polymerization of methyl methacrylate, methacrylic acid, and two different associative macromonomers. The polymerization kinetics showed good living character including well‐controlled molar mass, molar mass linearly increasing with conversion, and the ability to chain‐extend by forming an AB block copolymer. The steady‐shear and dynamic properties of a core‐shell emulsion, thickened with the different model alkali‐soluble rheology modifiers, were measured at constant pH and temperature. The steady‐shear data for latex solutions with conventional rheology modifiers exhibited the expected thickening, whereas the associative rheology modifiers showed contrasting rheology behavior. The dynamic measurements revealed that the latex solutions thickened with the conventional rheology modifiers exhibit solid‐like (dominant G′) behavior as compared with the associative rheology modifiers that give the latex solution a liquid‐like (dominant G″) character. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 223–235, 2003 相似文献
16.
Xylitol production by Debaryomyces hansenii NRRL Y-7426 was performed on synthetic medium varying the initial xylose concentration between 50 and 300 g/L. The experimental
results of these tests were used to investigate the effect of substrate level on xylose consumption by this yeast. Satisfactory
values of product yield on substrate (0.74–0.83 g/g) as well as volumetric productivity (0.481–0.694 g/L·h) were obtained
over a wide range of xylose levels (90–200 g/L), while a worsening of kinetic parameters took place at higher concentration,
likely due to a substrate inhibition phenomenon. The metabolic behavior of D. hansenii was studied, under these conditions, through a carbon material balance to estimate the fractions of xylose consumed by the
cell for different activities (xylitol production, biomass growth, and respiration) during the lag, exponential, and stationary
phases. 相似文献
17.
The effects of electric charge interation and particle correlations on suspension rheology are examined. A one-component fluid analysis using a Smoluchowski equation for the equilibrium structure is applied to charged suspensions of spherical colloids under shear. The frequency dependent modulus and viscosity, predicted as functions of particle and added salt concentrations, are compared with published rheological measurements on model suspensions. Recent improvements in the statistical mechanical theories for the equilibrium microstructure, its nonequilibrium deformation, and the bulk shear stresses are included. The direct electrostatic interaction is found to drive the divergence in the shear viscosity near the liquid-solid phase transition. Extensions of the theory predict the elastic modulus of binary mixtures of charged colloids. Estimates of the primary electroviscous effect, hydrodynamic interactions, and errors in the Yukawa limiting form for the potential and applications of asymptotic theories are presented. Predictions for the rheology based on effective hard-sphere models are found to be reasonable when using a parameter fit from the equilibrium phase behavior. Mean-field mode coupling theories predict larger relaxation times than calculated from the Smoluchowski equation (=SE). A study of binary mixing effects on elasticity shows non-ideal behavior. It is noted that equilibrium structural information can be used to resolve discrepancies between the theoretical predictions and the measured rheology. 相似文献
18.
Using the simultaneoussaccharification and fermentation (SSF) technique, pulp mill solid waste cellulose was converted into
glucose using cellulase enzyme and glucose into lacticacid using NRRL B445. SSF experiments were conducted at various pH levels,
temperatures, and nutrient concentrations, and the lactic acid yield ranged from 86 to 97%. The depletion of xylose in SSF
was further investigated by inoculating NRRL B445 into a xylose-only medium. On prolonged incubation, depletion of xylose
with lactic acid production was observed. An experimental procedure with a nonglucose medium was developed to eliminate the
lag phase. From xylose fermentation, Lactobacillus delbrueckii yielded 88–92% lactic acid and 2–12% acetic acid. 相似文献
19.
Claudia I. Ishizawa Tina Jeoh William S. Adney Michael E. Himmel David K. Johnson Mark F. Davis 《Cellulose (London, England)》2009,16(4):677-686
It has previously been shown that the improved digestibility of dilute acid pretreated corn stover is at least partially due
to the removal of xylan and the consequent increase in accessibility of the cellulose to cellobiohydrolase enzymes. We now
report on the impact that lignin removal has on the accessibility and digestibility of dilute acid pretreated corn stover.
Samples of corn stover were subjected to dilute sulfuric acid pretreatment with and without simultaneous (partial) lignin
removal. In addition, some samples were completely delignified after the pretreatment step using acidified sodium chlorite.
The accessibility and digestibility of the samples were tested using a fluorescence-labeled cellobiohydrolase (Trichoderma reesei Cel7A) purified from a commercial cellulase preparation. Partial delignification of corn stover during dilute acid pretreatment
was shown to improve cellulose digestibility by T. reesei Cel7A; however, decreasing the lignin content below 5% (g g−1) by treatment with acidified sodium chlorite resulted in a dramatic reduction in cellulose digestibility. Importantly, this
effect was found to be enhanced in samples with lower xylan contents suggesting that the near complete removal of xylan and
lignin may cause aggregation of the cellulose microfibrils resulting in decreased cellulase accessibility. 相似文献
20.
Corn stover, a well-known example of lignocellulosic biomass, is a potential renewable feed for bioethanol production. Dilute
sulfuric acid pretreatment removes hemicellulose and makes the cellulose more susceptible to bacterial digestion. The rheologic
properties of corn stover pretreated in such a manner were studied. The Power Law parameters were sensitive to corn stover
suspension concentration becoming more non-Newtonian with slope n, ranging from 0.92 to 0.05 between 5 and 30% solids. The Casson and the Power Law models described the experimental data
with correlation coefficients ranging from 0.90 to 0.99 and 0.85 to 0.99, respectively. The yield stress predicted by direct
data extrapolation and by the Herschel-Bulkley model was similar for each concentration of corn stover tested. 相似文献