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1.
Avicel enrichment cultures from 47 thermal-pool sites in the New Zealand Rotorua-Taupo region were screened for growth and carboxymethyl cellulase activity at 75°C. Eight anaerobic cellulolytic cultures were obtained. The effect of temperature on carboxymethyl cellulase activity was measured, and bacteria were isolated from the five best cultures. Bacteria from two sources designated TP8 and TP10 grew at 75°C, accumulated reducing sugar in the growth medium and gave free cellulases with avicelase activity. Bacteria from sources designated Tok4, Tok8, and Wai21 grew at 75°C, accumulated no free sugars in the medium, and gave free carboxymethyl cellulases with virtually no avicelase activity. All were obligate anaerobic nonsporeforming rods which stained gram negative, grew on pentoses as well as hexoses, and gave ethanol and acetate as major fermentation end products. The isolated strain which produced the most active and stable cellulases (trivially designated TP8.T) had lower rates of free endocellulase accumulation at 75°C than did Clostridium thermocellum at 60°C, but its cellulase activity against avicel and filter paper in culture supernatants was comparable. Tested at 85°C, TP8.T carboxymethyl cellulases included components which were very stable, whereas C. thermocellum carboxymethyl cellulases were all rapidly inactivated. The TP8.T avicelase activity was relatively unaffected by Triton X-100, EDTA, and dithiothreitol. Evidence was obtained for the existence of unisolated, cellulolytic extreme thermophiles producing cellulases which were more stable and active than those from TP8.T.  相似文献   

2.
Sporotrichum thermophile Apinis, was the most active carboxymethyl-cellulose (CMC)-ase producer among seven thermophilic and four thermotolerant fungal species isolated from Egyptian soil and screened for their ability to produce extracellular cellulase in culture media containing CMC as a sole carbon source. The fungus also efficiently hydrolysed filter paper cellulose. Comparison of various untreated and alkali-treated cellulosic and lignocellulosic materials as substrates for cellulase production by S. thermophile revealed the most easily degraded substrate was sugarcane bagasse at 2% concentration. This substrate when alkali treated was the most susceptible to enzymic hydrolysis by culture filtrates of S. thermophile grown on untreated bagasse. Optimum hydrolysis was obtained after 18 h incubation with the filtrate at pH 3·5–4 and 45°C. Alkali treatment of bagasse reduced its lignin content significantly and the culture filtrate of S. thermophile grown on untreated bagasse was found to contain xylanase and polygalacturonase in addition to cellulase and cellobiase.  相似文献   

3.
Sugarcane bagasse (SCB), a lignocellulosic byproduct of juice extraction from sugarcane, is rich in cellulose (40-42%). This could be used as a substrate for the production of cellulase complex. Fermentation conditions were optimized for production of cellulase complex (CMCase, Cellulobiase and FPase) by wild type Trichoderma sp. using sugarcane bagasse as sole carbon source. Alkaline treatment (2% NaOH) of bagasse (AlSCB) was found suitable for the production of reducing sugar over the acidic pretreatment method. After 5 days of incubation period, 5% substrate concentration at pH 5.0 and 400C resulted in maximum production of CMCase (0.622 U), while maximum (3.388 U) production of cellulobiase was obtained at 300C. The CMCase was precipitated and purified to the extent of 59.06 fold by affinity chromatography with 49.09% recovery. On 12% SDS-PAGE, a single band corresponding to 33 kDa was observed. The Km and Vmax for CMCase from Trichoderma was found 507.04 mg/ml and 65.32 mM/min, respectively. The enzyme exhibited maximum activity at 300C at pH-5.0 (0.363 U) and was stable over range of 20-60°C and pH 5.0-7.5.  相似文献   

4.
Cellulases play a key role in enzymatic routes for degradation of plant cell-wall polysaccharides into simple and economically-relevant sugars. However, their low performance on complex substrates and reduced stability under industrial conditions remain the main obstacle for the large-scale production of cellulose-derived products and biofuels. Thus, in this study a novel cellulase with unusual catalytic properties from sugarcane soil metagenome (CelE1) was isolated and characterized. The polypeptide deduced from the celE1 gene encodes a unique glycoside hydrolase domain belonging to GH5 family. The recombinant enzyme was active on both carboxymethyl cellulose and β-glucan with an endo-acting mode according to capillary electrophoretic analysis of cleavage products. CelE1 showed optimum hydrolytic activity at pH 7.0 and 50 °C with remarkable activity at alkaline conditions that is attractive for industrial applications in which conventional acidic cellulases are not suitable. Moreover, its three-dimensional structure was determined at 1.8 Å resolution that allowed the identification of an insertion of eight residues in the β8-α8 loop of the catalytic domain of CelE1, which is not conserved in its psychrophilic orthologs. This 8-residue-long segment is a prominent and distinguishing feature of thermotolerant cellulases 5 suggesting that it might be involved with thermal stability. Based on its unconventional characteristics, CelE1 could be potentially employed in biotechnological processes that require thermotolerant and alkaline cellulases.  相似文献   

5.
The objective of this work is to investigate the utilization of two abundant agricultural residues in Brazil for the production and application of cellulolytic enzymes. Different materials obtained after pretreatment of sugarcane bagasse, as well as pure synthetic substrates, were considered for cellulase production by Penicillium funiculosum. The best results for FPase (354 U L?1) and β-glucosidase (1,835 U L?1) production were observed when sugarcane bagasse partially delignified cellulignin (PDC) was used. The crude extract obtained from PDC fermentation was then partially characterized. Optimal temperatures for cellulase action ranged from 52 to 58°C and pH values of around 4.9 contributed to maximum enzyme activity. At 37°C, the cellulases were highly stable, losing less than 15% of their initial activity after 23 h of incubation. There was no detection of proteases in the P. funiculosum extract, but other hydrolases, such as endoxylanases, were identified (147 U L?1). Finally, when compared to commercial preparations, the cellulolytic complex from P. funiculosum showed more well-balanced amounts of β-glucosidase, endo- and exoglucanase, resulting in the desired performance in the presence of a lignocellulosic material. Cellulases from this filamentous fungus had a higher glucose production rate (470 mg L?1 h?1) when incubated with corn cob than with Celluclast®, GC 220® and Spezyme® (312, 454 and 400 mg L?1 h?1, respectively).  相似文献   

6.
The effect of temperature, pH, and sodium chloride concentration on the growth of the Ascomycetes fungus Monascus ruber van Tieghem, the main spoilage microorganism during storage of table olives, was studied by using the gradient plate technique. Gradients of NaCl (3 to 9%, wt/vol) at right angles to gradients of pH (2 to 6.8) were prepared for the plates, which were incubated at 25, 30, and 35°C. Visible fungal growth, expressed in optical density units, was recorded by image analysis and graphically presented in the form of three-dimensional grids. Results obtained from the plates indicated that the fungus was salt and acid tolerant, being able to grow at NaCl concentrations of up to 9% (wt/vol) and pH values of as low as 2.2, depending on the incubation temperature. The inhibitory effect of NaCl increased as the pH decreased progressively at 25 and 30°C but not at 35°C. Growth was better at 30 and 25°C as judged by the larger extent of the plates covered by mycelium compared with that at 35°C, where no growth was observed at pHs below 3.7. Differentiation between vegetative (imperfect-stage) and reproductive (perfect-stage) growth was evident on all plates, providing useful information about the effect of environmental conditions on the form of fungal growth. When the growth/no-growth surface model was obtained by applying linear logistic regression, it was found that all factors (pH, NaCl, and temperature) and their interactions were significant. Plots of growth/no-growth interfaces for P values of 0.1, 0.5, and 0.9 described the results satisfactorily at 25 and 35°C, whereas at 35°C the model predicted lower minimum pH values for growth in the range of 7 to 10% NaCl than those observed on the plates. Overall, it is suggested that the fungus cannot be inhibited by any combination of pH and NaCl within the limits of the brine environment, so further processing is required to ensure product stability in the market.  相似文献   

7.
Summary L-Sorbose, which is known as an inhibitor of -1,3-glucan synthesis in fungi, induces the production of cellulases in strains belonging to Trichoderma reesei. Especially, mutant strains PC-3–7 and X-31, which were obtained by several steps of mutation from QM 9414, have the most effective cellulase inducibility by L-sorbose comparing with other mutants of Trichoderma reesei. They synthesized cellulases effectively in liquid culture, whenever the alkaline treated sugarcane bagasse was used as a main carbon source for lowering the cost of cellulase production.  相似文献   

8.
The production of biofuels from lignocellulosic biomass appears to be attractive and viable due to the abundance and availability of this biomass. The hydrolysis of this biomass, however, is challenging because of the complex lignocellulosic structure. The ability to produce hydrolytic cellulase enzymes in a cost-effective manner will certainly accelerate the process of making lignocellulosic ethanol production a commercial reality. These cellulases may need to be produced aerobically to generate large amounts of protein in a short time or anaerobically to produce biofuels from cellulose via consolidated bioprocessing. Therefore, it is important to identify a promoter that can constitutively drive the expression of cellulases under both aerobic and anaerobic conditions without the need for an inducer. Using lacZ as reporter gene, we analyzed the strength of the promoters of four genes, namely lacZ, gapA, ldhA and pflB, and found that the gapA promoter yielded the maximum expression of the β-galactosidase enzyme under both aerobic and anaerobic conditions. We further cloned the genes for two cellulolytic enzymes, β-1,4-endoglucanase and β-1,4-glucosidase, under the control of the gapA promoter, and we expressed these genes in Escherichia coli, which secreted the products into the extracellular medium. An ethanologenic E. colistrain transformed with the secretory β-glucosidase gene construct fermented cellobiose in both defined and complex medium. This recombinant strain also fermented wheat straw hydrolysate containing glucose, xylose and cellobiose into ethanol with an 85% efficiency of biotransformation. An ethanologenic strain that constitutively secretes a cellulolytic enzyme is a promising platform for producing lignocellulosic ethanol.  相似文献   

9.
Lactic acid is one of the top 30 potential building-block chemicals from biomass, of which the most extensive use is in the polymerization of lactic acid to poly-lactic-acid (PLA). To reduce the cost of PLA, the search for cheap raw materials and low-cost process for lactic acid production is highly desired. In this study, the final titer of produced L-lactic acid reached a concentration of 185 g·L−1 with a volumetric productivity of 1.93 g·L−1·h−1 by using sugarcane bagasse hydrolysate as the sole carbon source simultaneously with cottonseed meal as cheap nitrogen sources under the open fed-batch fermentation process. Furthermore, a lactic acid yield of 0.99 g per g of total reducing sugars was obtained, which is very close to the theoretical value (1.0 g g−1). No D-isomer of lactic acid was detected in the broth, and thereafter resulted in an optical purity of 100%, which exceeds the requirement of lactate polymerization process. To our knowledge, this is the best performance of fermentation on polymer-grade L-lactic acid production totally using lignocellulosic sources. The high levels of optically pure l-lactic acid produced, combined with the ease of handling and low costs associated with the open fermentation strategy, indicated the thermotolerant Bacillus sp. P38 could be an excellent candidate strain with great industrial potential for polymer-grade L-lactic acid production from various cellulosic biomasses.  相似文献   

10.
Cellulase production by a thermophilic clostridium species   总被引:8,自引:5,他引:3       下载免费PDF全文
Strain M7, a thermophilic, anaerobic, terminally sporing bacterium (0.6 by 4.0 μm) was isolated from manure. It degraded filter paper in 1 to 2 days at 60 C in a minimal cellulose medium but was stimulated by yeast extract. It fermented a wide variety of sugars but produced cellulase only in cellulose or carboxymethyl-cellulose media. Cellulase synthesis not only was probably repressed by 0.4% glucose and 0.3% cellobiose, but also cellulase activity appeared to be inhibited by these sugars at these concentrations. Both C1 cellulase (degrades native cellulose) and Cx cellulase (β-1,4-glucanase) activities in strain M7 cultures were assayed by measuring the liberation of reducing sugars with dinitrosalicylic acid. Both activities had optima at pH 6.5 and 67 C. One milliliter of a 48-h culture of strain M7 hydrolyzed 0.044-meq of glucose per min from cotton fibers. The cellulase(s) from strain M7 was extracellular, produced during exponential growth, but was not free in the growth medium until approximately 30% of the cellulose was hydrolyzed. Glucose and cellobiose were the major soluble products liberated from cellulose by the cellulase. ZnCl2 precipitation appeared initially to be a good method for the concentration of cellulase activity, but subsequent purification was not successful. Isoelectric focusing indicated the presence of four Cx cellulases (pI 4.5, 6.3, 6.8, and 8.7). The rapid production and high activity of cellulases from this organism strongly support the basic premise that increased hydrolysis of native cellulose is possible at elevated temperature.  相似文献   

11.
Since Saccharomyces cerevisiae lacks the cellulase complexes that hydrolyze cellulosic materials, which are abundant in the world, two types of hydrolytic enzymes involved in the degradation of cellulosic materials to glucose were genetically co-immobilized on its cell surface for direct utilization of cellulosic materials, one of the final goals of our studies. The genes encoding FI-carboxymethylcellulase (CMCase) and β-glucosidase from the fungus Aspergillus aculeatus were individually fused with the gene encoding the C-terminal half (320 amino acid residues from the C terminus) of yeast α-agglutinin and introduced into S. cerevisiae. The delivery of CMCase and β-glucosidase to the cell surface was carried out by the secretion signal sequence of the native signal sequence of CMCase and by the secretion signal sequence of glucoamylase from Rhizopus oryzae for β-glucosidase, respectively. The genes were expressed by the glyceraldehyde-3-phosphate dehydrogenase promoter from S. cerevisiae. The CMCase and β-glucosidase activities were detected in the cell pellet fraction, not in the culture supernatant. The display of CMCase and β-glucosidase proteins on the cell surface was confirmed by immunofluorescence microscopy. The cells displaying these cellulases could grow on cellobiose or water-soluble cellooligosaccharides as the sole carbon source. The degradation and assimilation of cellooligosaccharides were confirmed by thin-layer chromatography. This result showed that the cell surface-engineered yeast with these enzymes can be endowed with the ability to assimilate cellooligosaccharides. This is the first step in the assimilation of cellulosic materials by S. cerevisiae expressing heterologous cellulase genes.  相似文献   

12.
Twelve white-rot fungi were grown in solid-state culture on lemon grass (Cymbopogon citratus) and citronella (Cymbopogon winterianus) bagasse. The two lignocellulosic substrates had 11% permanganate lignin and a holocellulose fraction of 58%. After 5 to 6 weeks at 20°C, nine fungi produced a solid residue from lemon grass with a higher in vitro dry matter enzyme digestibility than the original bagasse; seven did the same for citronella. The best fungus for both substrates was Bondarzewia berkeleyi; it increased the in vitro dry matter enzyme digestibility to 22 and 24% for lemon grass and citronella, respectively. The increases were correlated with weight loss and lignin loss. All fungi decreased lignin contents: 36% of the original value for lemon grass and 28% for citronella. Practically all fungi showed a preference for hemicellulose over cellulose.  相似文献   

13.
纤维素酶在饲料、造纸、纺织和纤维素乙醇生产等领域有重要用途,因而备受关注.使用稻草为唯一碳源进行纤维素降解微生物的富集,从云南大理苍山地区的土壤样品中筛选获得1株纤维素降解真菌DLCS-F18,其适宜生长温度为15-40℃、pH 2.0-13.0.通过形态学和ITS rRNA分子生物学鉴定,菌株DLCS-F18被鉴定为...  相似文献   

14.
We characterized the effect of deletion of the Trichoderma reesei (Hypocrea jecorina) ace1 gene encoding the novel cellulase regulator ACEI that was isolated based on its ability to bind to and activate in vivo in Saccharomyces cerevisiae the promoter of the main cellulase gene, cbh1. Deletion of ace1 resulted in an increase in the expression of all the main cellulase genes and two xylanase genes in sophorose- and cellulose-induced cultures, indicating that ACEI acts as a repressor of cellulase and xylanase expression. Growth of the strain with a deletion of the ace1 gene on different carbon sources was analyzed. On cellulose-based medium, on which cellulases are needed for growth, the Δace1 strain grew better than the host strain due to the increased cellulase production. On culture media containing sorbitol as the sole carbon source, the growth of the strain with a deletion of the ace1 gene was severely impaired, suggesting that ACEI regulates expression of other genes in addition to cellulase and xylanase genes. A strain with a deletion of the ace1 gene and with a deletion of the ace2 gene coding for the cellulase and xylanase activator ACEII expressed cellulases and xylanases similar to the Δace1 strain, indicating that yet another activator regulating cellulase and xylanase promoters was present.  相似文献   

15.
Several fungal endophytes of the Egyptian marine sponge Latrunculia corticata were isolated, including strains Trichoderma sp. Merv6, Penicillium sp. Merv2 and Aspergillus sp. Merv70. These fungi exhibited high cellulase activity using different lignocellulosic substrates in solid state fermentations (SSF). By applying mutagenesis and intergeneric protoplast fusion, we have obtained a recombinant strain (Tahrir-25) that overproduced cellulases (exo-β-1,4-glucanase, endo-β-1,4-glucanase and β-1,4-glucosidase) that facilitated complete cellulolysis of agricultural residues. The process parameters for cellulase production by strain Tahrir-25 were optimized in SSF. The highest cellulase recovery from fermentation slurries was achieved with 0.2% Tween 80 as leaching agent. Enzyme production was optimized under the following conditions: initial moisture content of 60% (v/w), inoculum size of 106 spores ml−1, average substrate particle size of 1.0 mm, mixture of sugarcane bagasse and corncob (2:1) as the carbon source supplemented with carboxymethyl cellulose (CMC) and corn steep solids, fermentation time of 7 days, medium pH of 5.5 at 30°C. These optimized conditions yielded 450, 191, and 225 units/gram dry substrate (U gds−1) of carboxylmethyl cellulase, filter-paperase (FPase), and β-glucosidase, respectively. Subsequent fermentation by the yeast, Saccharomyces cerevisiae NRC2, using lignocellulose hydrolysates obtained from the optimized cellulase process produced the highest amount of ethanol (58 g l−1). This study has revealed the potential of exploiting marine fungi for cost-effective production of cellulases for second generation bioethanol processes.  相似文献   

16.
Volvariella volvacea, commonly known as the straw or paddy mushroom, had the following growth characteristics: minimum temperature, 25°C; optimal temperature, 37°C; maximal temperature, 40°C; pH optimum 6.0. Optimal pH for cellulase production was 5.5. The optimal initial pH for cellulase production and mycelial growth was found to be 6.0. The pH and temperature optima for cellulolytic activity were 5.0 and 50°C, respectively. Maximal cellulolytic activity was obtained within 5 days in shake-flask culture. The cellulases were found to be partly cell free and partly cell bound during growth on microcrystalline cellulose. The endoglucanase activity was primarily extracellular, and β-glucosidase activity was found exclusively extracellularly. Weak cellulase activity was detected when cells were grown on cellobiose and lactose. V. volvacea could not digest the lignin portion of newspaper in shake-flask cultivation. Phenol oxidase, an important enzyme in lignin biodegradation, also was lacking in the cell-free filtrate. However, the organism oxidized phenolic compounds when it was cultured on agar plates containing commercial lignin.  相似文献   

17.
Sodium phosphate buffer was used to extract cellulases from the plant solids fraction of rumen contents. The mixed cellulase preparation had maximal activity at pH 6.9 and 49°C. The Vmax and the apparent Km for wheaten hay cellulose were 19.8 glucose units/min and 6.35 mg/ml, respectively, and for microcrystalline cellulose (Sigmacell) at the same enzyme concentration, they were 33 glucose units/min and 27.5 mg/ml, respectively. For these assays a glucose unit was defined as nanomoles of glucose plus twice the nanomoles of cellobiose. Consideration of thermodynamic and kinetic data suggested that the hydrolysis of a relatively labile arabino-xylan comprising 3% of the wheaten hay cellulose was dependent on prior removal of the protecting β-1,4-glucose chains at the outer surface of the cellulose preparation. Sequential removal of structural polysaccharides from the plant cell wall rendered the latter more susceptible to cellulase activity. Cellulase activity was stimulated by increasing the concentration of phosphate from 5 to 50 mM. The stimulation was magnified in the presence of cell-free rumen fluid. Cellulase activity was not stimulated by calcium, magnesium, iron, zinc, manganese, copper, or cobalt ions and was unaffected by the chelators ethylenediaminetetraacetic acid and ethyleneglycol-bis (β-aminoethyl ether)-N,N′-tetraacetic acid. O-phenanthroline inhibited activity by 30 to 50%, but this may have been due to nonchelate properties. Anaerobic conditions or thiol protective agents were not essential for either the activity or stability of the cellulases during assay. An ultrafiltrable inhibitor of cellulase activity was detected in cell-free rumen fluid.  相似文献   

18.
Metagenomics has been widely employed for discovery of new enzymes and pathways to conversion of lignocellulosic biomass to fuels and chemicals. In this context, the present study reports the isolation, recombinant expression, biochemical and structural characterization of a novel endoxylanase family GH10 (SCXyl) identified from sugarcane soil metagenome. The recombinant SCXyl was highly active against xylan from beechwood and showed optimal enzyme activity at pH 6,0 and 45°C. The crystal structure was solved at 2.75 Å resolution, revealing the classical (β/α)8-barrel fold with a conserved active-site pocket and an inherent flexibility of the Trp281-Arg291 loop that can adopt distinct conformational states depending on substrate binding. The capillary electrophoresis analysis of degradation products evidenced that the enzyme displays unusual capacity to degrade small xylooligosaccharides, such as xylotriose, which is consistent to the hydrophobic contacts at the +1 subsite and low-binding energies of subsites that are distant from the site of hydrolysis. The main reaction products from xylan polymers and phosphoric acid-pretreated sugarcane bagasse (PASB) were xylooligosaccharides, but, after a longer incubation time, xylobiose and xylose were also formed. Moreover, the use of SCXyl as pre-treatment step of PASB, prior to the addition of commercial cellulolytic cocktail, significantly enhanced the saccharification process. All these characteristics demonstrate the advantageous application of this enzyme in several biotechnological processes in food and feed industry and also in the enzymatic pretreatment of biomass for feedstock and ethanol production.  相似文献   

19.
20.
The wide variety of bacteria in the environment permits screening for more efficient cellulases to help overcome current challenges in biofuel production. This study focuses on the isolation of efficient cellulase producing bacteria found in organic fertilizers and paper mill sludges which can be considered for use in large scale biorefining. Pure isolate cultures were screened for cellulase activity. Six isolates: S1, S2, S3, S4, E2, and E4, produced halos greater in diameter than the positive control (Cellulomonas xylanilytica), suggesting high cellulase activities. A portion of the 16S rDNA genes of cellulase positive isolates were amplified and sequenced, then BLASTed to determine likely genera. Phylogenetic analysis revealed genera belonging to two major Phyla of Gram positive bacteria: Firmicutes and Actinobacteria. All isolates were tested for the visible degradation of filter paper; only isolates E2 and E4 (Paenibacillus species) were observed to completely break down filter paper within 72 and 96 h incubation, respectively, under limited oxygen condition. Thus E2 and E4 were selected for the FP assay for quantification of total cellulase activities. It was shown that 1% (w/v) CMC could induce total cellulase activities of 1652.2±61.5 and 1456.5±30.7 μM of glucose equivalents for E2 and E4, respectively. CMC could induce cellulase activities 8 and 5.6X greater than FP, therefore CMC represented a good inducing substrate for cellulase production. The genus Paenibacillus are known to contain some excellent cellulase producing strains, E2 and E4 displayed superior cellulase activities and represent excellent candidates for further cellulase analysis and characterization.  相似文献   

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