Inductive formation of cellulase by sophorose in Trichoderma viride

Cellulose Degradation Enzymes in Filamentous Fungi, A Bioprocessing Approach Towards Biorefinery

The economic exploration of renewable energy resources has hot fundamentals among the countries besides dwindling energy resources and increasing public pressure. Cellulose accumulation is a major bio-natural resource from agricultural waste. Cellulases are the most potential enzymes that systematically degrade cellulosic biomass into monomers which could be further processed into several efficient value-added products via chemical and biological reactions including useful biomaterial for human benefits. This could lower the environmental risks problems followed by an energy crisis. Cellulases are mainly synthesized by special fungal genotypes. The strain Trichoderma orientalis could highly express cellulases and was regarded as an ideal strain for further research, as the genetic tools have found compatibility for cellulose breakdown by producing effective cellulose-degrading enzymes. This strain has found a cellulase production of about 35 g/L that needs further studies for advancement. The enzyme activity of strain Trichoderma orientalis needed to be further improved from a molecular level which is one of the important methods. Considering synthetic biological approaches to unveil the genetic tools will boost the knowledge about commercial cellulases bioproduction. Several genetic transformation methods were significantly cited in this study. The transformation approaches that are currently researchers are exploring is transcription regulatory factors that are deeply explained in this study, that are considered essential regulators of gene expression.

A comprehensive review on the properties, production, and applications of functional glucobioses

Glucobiose is a range of disaccharides consisting of two glucose molecules, generally including trehalose, kojibiose, sophorose, nigerose, laminaribiose, maltose, cellobiose, isomaltose, and gentiobiose. The difference glycosidic bonds of two glucose molecules result in the diverse molecular structures, physiochemical properties and physiological functions of these glucobioses. Some glucobioses are abundant in nature but have unconspicuous roles on health like maltose, whereas some rare glucobioses display remarkable biological effects. It is unpractical process to extract these rare glucobioses from natural resources, while biological synthesis is a feasible approach. Recently, the production and application of glucobiose have attracted considerable attention. This review provides a comprehensive overview of glucobioses, including their natural sources and physicochemical properties like structure, sweetness, digestive performance, toxicology, and cariogenicity. Specific enzymes used for the production of various glucobioses and fermentation production processes are summarized. Additionally, their versatile functions and broad applications are also introduced.

Optimization of Arundo donax Saccharification by (Hemi)cellulolytic Enzymes from Pleurotus ostreatus

An enzymatic mixture of cellulases and xylanases was produced by Pleurotus ostreatus using microcrystalline cellulose as inducer, partially characterized and tested in the statistical analysis of Arundo donax bioconversion. The Plackett-Burman screening design was applied to identify the most significant parameters for the enzymatic hydrolysis of pretreated A. donax. As the most significant influence during the enzymatic hydrolysis of A. donax was exercised by the temperature (°C), pH, and time, the combined effect of these factors in the bioconversion by P. ostreatus cellulase and xylanase was analyzed by a 3(3) factorial experimental design. It is worth noting that the best result of 480.10 mg of sugars/gds, obtained at 45 °C, pH 3.5, and 96 hours of incubation, was significant also when compared with the results previously reached by process optimization with commercial enzymes.

Cellulase production by a thermophilic clostridium species

Strain M7, a thermophilic, anaerobic, terminally sporing bacterium (0.6 by 4.0 mum) 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 C(1) cellulase (degrades native cellulose) and C(x) cellulase (beta-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. ZnCl(2) 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 C(x) 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.

Cellulose degrading enzymes and their potential industrial applications

Bioconversion of cellulose to soluble sugars and glucose is catalyzed by a group of enzymes called cellulases. Microorganisms including fungi, bacteria and actinomycetes produce mainly three types of cellulase components--endo-1,4-beta-D-glucanase, exo-1,4-beta-D-glucanase and beta-glucosidase--either separately or in the form of a complex. Over the last several decades, cellulases have become better understood at a fundamental level; nevertheless, much remains to be learnt. The tremendous commercial potential of cellulases in a variety of applications remains the driving force for research in this area. This review summarizes the present state of knowledge on microbial cellulases and their applications.

ACEII, a novel transcriptional activator involved in regulation of cellulase and xylanase genes of Trichoderma reesei

A novel yeast-based method to isolate transcriptional activators was applied to clone regulators binding to the cellulase promoter cbh1 of the filamentous fungus Trichoderma reesei (Hypocrea jecorina). This led to the isolation of the cellulase activator ace2 encoding for a protein belonging to the class of zinc binuclear cluster proteins found exclusively in fungi. The DNA-binding domain of ACEII was expressed as a glutathione S-transferase fusion protein in Escherichia coli, and ACEII was shown to bind in vitro to the 5'-GGCTAATAA site present in the cbh1 promoter. This site also contains the proposed binding sequence of the xylanase activator XlnR of Aspergillus niger. Mutation of the GGC triplet abolished ACEII binding. The function of ACEII was studied by analyzing the effects of ace2 deletion in the hypercellulolytic T. reesei strain ALKO2221. Deletion of the ace2 gene led to lowered induction kinetics of mRNAs encoding the major cellulases cellobiohydrolases I and II and endoglucanases I and II and to 30-70% reduced cellulase activity when the fungus was grown on medium containing Solka floc cellulose. The expression level of the gene encoding xylanase was also affected. ace2 deletion led to lowered xyn2 expression in cellulose-induced cultivation. Cellulase induction by sophorose was not affected by ace2 deletion.

Regulation of cellulase gene expression in the filamentous fungus Trichoderma reesei

Basic features of regulation of expression of the genes encoding the cellulases of the filamentous fungus Trichoderma reesei QM9414, the genes cbh1 and cbh2 encoding cellobiohydrolases and the genes egl1, egl2 and egl5 encoding endoglucanases, were studied at the mRNA level. The cellulase genes were coordinately expressed under all conditions studied, with the steady-state mRNA levels of cbh1 being the highest. Solka floc cellulose and the disaccharide sophorose induced expression to almost the same level. Moderate expression was observed when cellobiose or lactose was used as the carbon source. It was found that glycerol and sorbitol do not promote expression but, unlike glucose, do not inhibit it either, because the addition of 1 to 2 mM sophorose to glycerol or sorbitol cultures provokes high cellulase expression levels. These carbon sources thus provide a useful means to study cellulase regulation without significantly affecting the growth of the fungus. RNA slot blot experiments showed that no expression could be observed on glucose-containing medium and that high glucose levels abolish the inducing effect of sophorose. The results clearly show that distinct and clear-cut mechanisms of induction and glucose repression regulate cellulase expression in an actively growing fungus. However, derepression of cellulase expression occurs without apparent addition of an inducer once glucose has been depleted from the medium. This expression seems not to arise simply from starvation, since the lack of carbon or nitrogen as such is not sufficient to trigger significant expression.

Synthesis of isopropyl-1-thio-beta-D-glucopyranoside (IPTGlc), an inducer of Aspergillus niger B1 beta-glucosidase production

Production of beta-glucosidase in Aspergillus niger B1 is subjected to catabolic repression by glucose. Aspergillus niger B1 grown on bran as a carbon source secreted beta-glucosidase. The maximum level of the enzyme was reached after 7 d of fermentation. Addition of 1% glucose to the medium suppressed beta-glucosidase production to undetectable levels. In this study, the organic synthesis of a potential inducer of beta-glucosidase production by A. niger B1's reported. Isopropyl-1-thio-beta-D-glucopyranoside (IPTGlc) was synthesized using a two-step organic synthesis protocol. The H-NMR data agreed with those reported previously for the galactoside analog. When IPTGlc was added 24 h after inoculation at a final concentration of 0.4 mM, similar levels of beta-glucosidase were reached 3 to 4 d earlier as compared to fermentation without IPTGlc induction. In practice, this may translate to a more efficient method of producing beta-glucosidase from this fungus.

Effects of disruption of xylanase-encoding genes on the xylanolytic system of Streptomyces lividans

Wild-type Streptomyces lividans produced the three xylanases (XlnA, XlnB, and XlnC) when xylan, xylan hydrolysates obtained by the action of XlnA, XlnB, and XlnC, or purified small xylo-oligosaccharides (xylobiose [X2], xylotriose [X3], xylotetraose [X4], and xylopentaose [X5]) were used as the carbon source. The three xylanase genes of S. lividans (xlnA, xlnB, and xlnC) were disrupted by using vectors that integrate into the respective genes. Disruption of one or more of the xln genes resulted in reduced growth rates and reduced total xylanase activities when the strain was grown in xylan. The greatest effect was observed when xlnA was disrupted. In medium containing xylan, disruption of xlnA did not affect expression of xlnB and xlnC; disruption of xlnB did not affect expression of xlnA but affected expression of xlnC; and disruption of xlnC did not affect expression of xlnA but affected expression of xlnB. A fraction of XlnB or XlnC hydrolytic products (those with a degree of polymerization greater than 11 [X11]) was found to stimulate expression of xlnB and xlnC in strains disrupted in xlnC and xlnB, respectively, whereas lower-molecular-weight fractions as well as purified small xylo-oligosaccharides did not. The stimulating molecule(s) lost its effect when it was hydrolyzed further by XlnA. A mechanism of transglycosylation reactions by the S. lividans xylanases is postulated to be involved in the regulation of xln genes.

The Trichoderma cellulase regulatory puzzle: from the interior life of a secretory fungus

Novel applications for cellulases have reinitiated interest in the regulation of production of these enzymes by the soft rot fungus Trichoderma reesei and related species. This paper reviews the current state of knowledge concerning the question "How can insoluble molecules like cellulose initiate their own breakdown by a microorganism?" The evidence available--based on biochemical as well as molecular biological approaches--favors a model in which conidial bound cellobiohydrolases carry out a first exo-exo-wise attack on the cellulose molecule. The disaccharides so formed (cellobiose, alpha-cellobiono-1,5-lactone) are then taken up by the mycelia and promote further cellulase biosynthesis. Evidence available suggests that they are further metabolized to, rather than being, the "true" inducer. Speculations on the nature of the inducer are presented. The roles of the beta-glucosidases of Trichoderma in this process are discussed. The pathway of cellulase secretion is discussed on the basis of electron microscopical as well as gene sequence information.

Positional isomers of thioxylobiose, their synthesis and inducing ability for D-xylan-degrading enzymes in the yeast Cryptococcus albidus

Isomeric S-linked 2-thioxylobiose 10, 3-thioxylobiose 17, and 4-thioxylobiose 19 were conveniently prepared by SN2 displacement of suitable triflylglycoses with the sodium salt of 2,3,4-tri-O-acetyl-1-thio-beta-D-glucopyranose, either in N,N-dimethylformamide, or in oxolan in the presence of a sodium complexing agent. Allyl 3,5-O-isopropylidene-2-O-trifluoromethanesulfonyl-beta-D-lyxofu ranoside was a convenient electrophilic precursor for 10, which was smoothly obtained after a short sequence of deprotection involving conversion to the 1-propenyl glycoside. 1,2:5,6-Di-O-isopropylidene-3-O-trifluoromethylsulfonyl-alpha-D-++ +allofuranose and 1,2,3-tri-O-benzoyl-4-O-trifluoromethylsulfonyl-beta-L-arabinop yranose were the respective precursors for 17 and 19. 4-Thioxylobiose has a highly stimulatory effect on the synthesis of enzymes of the xylanolytic system in the yeast Cryptococcus albidus when applied to the cells in the presence of the natural disaccharide inducer (1----4)-beta-D-xylobiose.

Induction of Cellulase by Gentiobiose and Its Sulfur-Containing Analog in Penicillium purpurogenum

Cellulase induction by β-glucodisaccharides was investigated by using non-cellulase-induced mycelia of Penicillium purpurogenum P-26, a highly-cellulase-producing fungus. Gentiobiose induced significant amounts of cellulase compared with cellobiose when nojirimycin was added to the induction medium to inhibit extracellular β-glucosidase activity. Thiogentiobiose (6- S -β- d -glucopyranosyl-6-thio- d -glucose), a sulfur-containing analog of gentiobiose, was more effective for cellulase induction than gentiobiose even in the absence of nojirimycin. Thiogentiobiose appeared to be a gratuitous inducer since it was not metabolized during cellulase induction. Gentiobiose was formed from cellobiose by the intracellular β-glucosidase of P. purpurogenum. These findings indicate that gentiobiose is an active inducer of cellulase for this fungus and may possibly be formed by intracellular β-glucosidase from cellobiose.

Interrelationship of Xylanase Induction and Cellulase Induction of Trichoderma longibrachiatum

Xylose oligomers rapidly induced xylanase activity of Trichoderma longibrachiatum, whereas induction was delayed in the presence of glucose. Cellobiose, cellopentaose, and xylobiose did not induce detectable levels of cellulase activity. However, mixtures of xylobiose with cellobiose or cellopentaose rapidly induced cellulase activity. In addition, mixtures of xylobiose with cellopentaose or cellobiose induced xylanase activity more effectively than xylobiose alone. Both xylanase and cellulase activity were detected after a lag period in the presence of lactose.

Regulatory aspects of cellulase biosynthesis and secretion

The cellulase enzyme system consists of cellobiohydrolase, endoglucanase, and beta-glucosidase and has been extensively studied with respect to its biosynthesis, properties, mode of action, application, and, most recently, secretion mechanisms. A knowledge of the factors governing the biosynthesis and secretion of these enzymes at the molecular level will be useful in maximizing enzyme productivity in extracellular fluid. Among other topics, the regulatory effects of sorbose (a noninducing sugar which is not a product of cellulose hydrolysis) on cellulase synthesis and release are described. Cellulase genes have recently been cloned into a number of microorganisms with a view to understanding the gene structure and expression and to obtaining the enzyme components in pure form. The factors governing biosynthesis and secretion of cellulases in recombinant cells are also discussed. Cellulases are known to be glycoproteins, therefore, the role of O- and N-linked glycosylation on enzyme stability and secretion is also detailed.

Induction and catabolite repression of cellulase in Penicillium funiculosum

The regulation of endoglucanase synthesis in Penicillium funiculosum is investigated using a method based on the viscosity lowering effect on carboxy methyl cellulose (CMC) by endoglucanase. Cellobiose (1 mg/L) causes induction, whereas glucose (5 g/L) does not repress the enzyme formation. Lactose (5 g/L) has no effect on the synthesis of cellulase. Avicel and cellulose powder (CP) are the best inducers of cellulase and xylanase activity. Both endoglucanase and xylanase activity were induced by CMC, whereas xylan induced only xylanase activity. The effect of protease on induction of cellulase activity is discussed.

Differential regulation of synthesis of multiple forms of specific endoglucanases by Trichoderma reesei QM9414

A method consisting of sodium dodecyl sulfate-polyacrylamide gel electrophoresis and subsequent detection of endoglucanases by blotting with a polyclonal antibody against endoglucanase I was used to investigate the effect of induction and carbon catabolite derepression on the synthesis of multiple forms of endoglucanase I by Trichoderma reesei. Five forms appeared upon growth on cellulose, whereas four and only two appeared upon growth on lactose (carbon catabolite derepression) and induction by sophorose in a resting cell system, respectively. All endoglucanases detected resembled endoglucanase I in their specificity, since they exhibited no activity toward xylan or paranitrophenyl-beta-D-lactobioside. A small (25-kilodalton) endoglucanase only appeared during growth on cellulose. None of the multiple forms arose by postsecretional modification. The results indicate that sophorose may not be the only compound mediating cellulose induction of the specific endoglucanases in T. reesei.

Glycosidic bond rearrangements in isomeric xylobioses by yeast xylan-degrading enzymes

The cells of Cryptococcus albidus induced for xylan-degrading enzymes are capable of transforming 1,2-beta-xylobiose and 1,3-beta-xylobiose into 1,4-beta-xylobiose, the natural inducer. The conversion involves transglycosylation and hydrolysis catalyzed by beta-xylosidase and beta-xylanase. A probable intermediate of the conversion of 1,2-beta-xylobiose was isolated and identified as a trisaccharide, 4-O-beta-xylopyranosyl-2-O-beta-xylopyranosyl-D-xylopyran ose. The trisaccharide is cleaved by purified endo-1,4-beta-xylanase of C. albidus mainly at the 1,2-beta-linkage yielding xylose and 1,4-beta-xylobiose.

Novel inducers of the xylan-degrading enzyme system of Cryptococcus albidus

A series of compounds structurally related to xylan and 1,4-beta-xylobiose were tested as inducers of the xylan-degrading enzyme system of Cryptococcus albidus. Washed, glucose-grown cells were incubated with alpha- and beta-linked xylobioses, 4-O-beta-D-xylopyranosyl-L-arabinopyranose, 3-O-beta-D-xylopyranosyl-xylobiose, 6-O-beta-D-xylopyranosyl-cellobiose, cellobiose, and methyl beta-D-xylopyranoside. All alpha-xylobioses and cellobiose were inactive as inducers of the xylan-degrading enzyme system. Other compounds served as inducers of varying efficiency, depending on their concentration in the induction medium and the time of incubation of cells. The most rapid response of the cells, i.e., the shortest induction period of beta-xyloside permease, beta-xylosidase (EC 3.2.1.37), and beta-xylanase (EC 3.2.1.8), was observed with 1,4-beta-xylobiose, which was the most efficient inducer at low concentrations (0.1 to 0.2 mM). At higher concentrations (2 to 10 mM) and after long incubations, the highest enzyme yields were obtained with 1,2-beta-xylobiose. The results represent a new example of efficient induction of polysaccharide-degrading enzyme systems by positional isomers of dimers derived from the polysaccharide.

Sophorose induction of an intracellular b-glucosidase in Trichoderma

The disaccharide sophorose induces Trichoderma to increase a soluble intracellular b-glucosidase that hydrolyses cellobiose, sophorose, and p-nitrophenyl-b-D-glucopyranoside. Simultaneously, it depresses the activity of a similar insoluble enzyme that is associated with the mycelium. Gel electrophoresis indicates that a single enzyme is responsible for all the soluble intracellular b-glucosidase activity. Cycloheximide severely inhibits sophorose induction of this enzyme indicating that the increase in activity normally obtained with sophorose is due to the de novo formation of the enzyme. The same sugars that promote the formation and release of cellulase by Trichoderma induce an increase in the soluble intracellular b-glucosidase. A function of the soluble intracellular enzyme appears to be the hydrolysis of cellobiose, which would otherwise accumulate during cellulose degradation, and thus to prevent cellobiose inhibition of cellulase.

Synthesis and hydrolysis of 1,3-beta-xylosidic linkages by endo-1,4-beta-xylanase of Cryptococcus albidus

Purified extracellular endo-1,4-beta-xylanase (EC 3.2.1.8) of the yeast Cryptococcus albidus was found to catalyze not only the known 1,4-beta-transfer, but an alternative transglycosylation reaction leading to the formation of 1,3-beta-glycosidic linkages. From a mixture of products of beta-xylanase degradation of phenyl beta-D-xylopyranoside three xylooligosaccharide fractions, differing chromatographically from the 1,4-beta-linked products, were isolated by preparative paper chromatography. Their structure was elucidated by mass spectrometry, 13C-NMR spectroscopy and enzymic hydrolysis by beta-xylanase and beta-xylosidase. The isomeric xylotriose was identified as 3-O-beta-D-xylopyranosyl-4-O-beta-D-xylopyranosyl-D-xylose. The fraction of isomeric tetrasaccharides was found to be represented mainly by 4-O-beta-D-xylopyranosyl-3-O-beta-D-xylopyranosyl-4-O-beta-D-xylopyranosyl- D-xylose. The xylooligosaccharides containing one 1,3-beta-linkage were also produced on the enzyme treatment of 1,4-beta-xylotriose and 1,4-beta-xylan. When treated with the enzyme responsible for their synthesis, the isomeric xylooligosaccharides were hydrolyzed at the 1,3-beta-linkage, despite the fact the enzyme does not attack 1,3-beta-xylan. The results are interpreted in the relation to the characterized four-subsite substrate-binding site of the enzyme.

Formation, Location, and Regulation of Endo-1,4-β-Glucanases and β-Glucosidases from Cellulomonas uda

The formation and location of endo-1,4-β-glucanases and β-glucosidases were studied in cultures of Cellulomonas uda grown on microcrystalline cellulose, carboxymethyl cellulose, printed newspaper, and some mono- or disaccharides. Endo-1,4-Glucanases were found to be extracellular, but a very small amount of cell-bound endo-1,4-β-glucanase was considered to be the basal endoglucanase level of the cells. The formation of extracellular endo-1,4-β-glucanases was induced by cellobiose and repressed by glucose. Extracellular endoglucanase activity was inhibited by cellobiose but not by glucose. β-Glucosidases, on the other hand, were formed constitutively and found to be cell bound. β-Glucosidase activity was inhibited noncompetitively by glucose. Some characteristics such as the optimal pH for and the thermostability of the endoglucanases and β-glucosidases and the end products of cellulose degradation were determined.

Effect of dithiocarbamates on cellulase activity in culture filtrates of Trichoderma reesei

Different concentrations of tetramethylthiuram disulfide (TMTD), sodium dimethyldithiocarbamate (NaDDC), and zinc dimethyldithiocarbamate (ZnDDC) affected the amount of cellulase(s) activity in the culture of Trichoderma reesei. After eight days incubation at 28 degrees C the greatest increase in Avicelase, CMCase, and beta-glucosidase over the control were observed at 0.1 ppm (TMTD) and 0.4 ppm (NaDDC and ZnDCC). There was decrease in the growth in the ZnDDC, but beta-glucosidase activity was reduced considerably. Total protein in the culture filtrate increased with the increase in cellulase(s) activity. No change in pH was observed at eight days incubation but pH increased (not exceeding 5.9) at 12 days incubation.

Repression of endo-1,4-beta-glucanase formation in Penicillium janthinellum and product inhibition of its 1,4-beta-glucanases and cellobiases

Endo-1,4-beta-glucanase formation of Penicillium janthinellum was repressed by glucose, sophorose, and glycerol. Chromatography on DEAE-Sephadex A-50 was employed to separate the 1,4-beta-glucanases from two cellobiases. The 1,4-beta-glucanases were inhibited competitively by cellobiose and glucose, and the two cellobiases were inhibited by glucose and glucono-delta-lactone.

Formation and Location of 1,4-β-Glucanases and 1,4-β-Glucosidases from Penicillium janthinellum

Formation and location of 1,4-β-glucanases and 1,4-β-glucosidases were studied in cultures of Penicillium janthinellum grown on Avicel, sodium carboxymethyl cellulose, cellobiose, glucose, mannose, and maltose. Endo-1,4-β-glucanases were found to be cell free, and their formation was induced by cellobiose. 1,4-β-Glucosidases, on the other hand, were formed constitutively and were primarily cell free, but with a small amount strongly associated with the cell wall. Low 1,4-β-glucosidase activities of periplasmic or intracellular origin were also found. A rotational viscosimetric method was developed to measure the total endo-1,4-β-glucanase activity of the culture (broth and solids). By this method, it was possible to determine the endo-1,4-β-glucanase activity not only in the supernatant of the culture but also on the surface of the mycelium or absorbed on residual Avicel. During a 70-liter batch cultivation of P. janthinellum , the adsorption of endo-1,4-β-glucanases by residual and newly added 10% Avicel was measured. The adsorption of soluble protein and endo-1,4-β-glucanases by Avicel was found to be largely independent of the pH value but dependent on temperature.

Regulation of the cellulolytic system in Trichoderma reesei by sophorose: induction of cellulase and repression of beta-glucosidase

Sophorose has two regulatory roles in the production of cellulase enzymes in Trichoderma reesei: beta-glucosidase repression and cellulase induction. Sophorose also is hydrolyzed by the mycelial-associated beta-glucosidase. Repression of beta-glucosidase reduces sophorose hydrolysis and thus may increase cellulase induction.

Induction and inducers of endo-1,4-beta-xylanase in the yeast Cryptococcus albidus

Extracellular endo-1,4-beta-xylanase synthesis in the yeast Cryptococcus albidus is largely inducible. During growth on wood xylans the yeast produces the enzyme in amounts two orders of magnitude greater than on other carbon sources, including xylose. The enzyme can be induced in washed glucose-grown cells by xylan and beta-1,4-xylooligosaccharides. Among the oligosaccharides only xylobiose was not degraded extracellularly, therefore it appears to be the natural inducer of the enzyme. Xylobiose as a metabolisable inducer is effective at low concentrations and constant availability to cells. At high concentration of xylobiose the inductive effect is less pronounced because of catabolic repression by degradation products. Methyl beta-D-xylopyranoside was found to serve as a non-utilizable inducer of beta-xylanase. The enzyme induced by the glycoside appears to be identical with that produced by the cells during growth on xylan.