Physiological studies on xylose induction and glucose repression of xylanolytic enzymes inAspergillus sydowiiMG49

Regulation of xylanase biosynthesis in Bacillus cereus BSA1

Microbial xylanases have a promising biotechnological potential to be used in industries. In this study, regulation of xylanase production was examined in Bacillus cereus BSA1. Xylanase production was induced by xylan. The enzyme production further increased in the presence of xylose and arabinose in very low concentration with addition of xylan (0.5% up to 6.02 U/ml). Addition of glucose (about 0.1%) to the media supplemented with xylan repressed xylanase production. Even higher concentration (>0.1%) of xylose and arabinose repressed xylanase biosynthesis. Glucose-mediated repression was partially relived by addition of cyclic adenosine monophosphate. Chemical like 2-4-dinitrophenol, which can inhibit adenosine triphosphate synthesis in cell, repressed xylanase synthesis and it suggested xylanase synthesis to be an energy dependent process.

Beta-xylanase from Thermomyces lanuginosus and its biobleaching application

Thermomyces lanuginosus is thermophilic fungus in which was isolated from widespread material. A high number of this fungus was found in composts especially mushroom composts. This fungus has been reported to produce a high level xylanase when cultivated in the medium containing xylan and corn cob as a carbon source. Various strains of T. lanuginosus produced a single xylanase with molecular masses in range of 22.0 to 29.0 kDa. Pure beta-xylanase obtained from various strains of this fungus exhibited highly stability at high temperature and wide pH range. The optimal temperature and optimal pH of pure beta-xylanase from various strains of T. lanuginosus have been reported in range of 60-75 degrees C and pH 6.0-7.0, respectively. The great thermal stability was resulting from the present of hydrophilic amino acid on beta sheet of the surface of xylanase structure. Moreover, the relatedness between high and low xylanase producing strains can be distinguish by random amplification of polymorphic DNA (RAPD). Based on nucleotide sequences and T. lanuginosus xylanase gene has been classified to be a member of family 11 (formerly known as cellulase family G) glycosyl hydrolases. This enzyme was endo-type xylanase having main product are xylose and xylobiose. The expression of xylanase gene from T. lanuginosus was achieved in Escherichia coli and methylotrophic yeast Pichia pastoris. The ability of T. lanuginosus in which produced large amount of high thermos stable xylanase has made this fungus to be a source of xylanase production for biobleaching in pulp and paper process.

Induction and repression of beta-xylanase of Thermomyces lanuginosus TISTR 3465

The effect of carbon sources on the production of beta-xylanase by Thermomyces lanuginosus TISTR 3465 was investigated. Xylan showed the highest inductive effect on the enzyme formation whereas xylobiose and xylooligosaccharides resulted in lesser effect. beta-Xylanase was also produced at low level with xylose as well as other sugars tested. Xylan concentration at 15 g L(-1) gave the maximum inductive effect on beta-xylanase formation, whereas xylooligosaccharides and xylose were effective at a lower concentration of 2.5 g L(-1). High concentrations of these sugars significantly repressed the enzyme formation. Crude enzyme from the supernatants, without and with other sugars produced a single xylanase band on non-denaturing PAGE gels. However, an intense xylanase activity band was observed from the supernatant of media with xylan, xylobiose and xylooligosaccharides as the carbon sources. An intense protein band of 24.9 kDa from the culture filtrate of xylan medium was observed. Xylan increased beta-xylanase production by the fungus 16-fold when it was added to the xylose medium after cultivation for 3 days. In contrast, addition of xylose to the xylan medium decreased beta-xylanase production 3-fold. A distinct appearance and disappearance of a 24.9 kDa protein and the activity band coincided with an increase and decrease of xylanase activity, respectively. This indicated the synthesis of xylanase by this strain was most induced by xylan. Moreover, the level of xylanase induction has no related to amino acid sequence of the enzyme.

Regulation of xylanase in Aspergillus phoenicis: a physiological and molecular approach

Microbial xylanolytic enzymes have a promising biotechnological potential, and are extensively applied in industries. In this study, induction of xylanolytic activity was examined in Aspergillus phoenicis. Xylanase activity induced by xylan, xylose or beta-methylxyloside was predominantly extracellular (93-97%). Addition of 1% glucose to media supplemented with xylan or xylose repressed xylanase production. Glucose repression was alleviated by addition of cAMP or dibutyryl-cAMP. These physiological observations were supported by a Northern analysis using part of the xylanase gene ApXLN as a probe. Gene transcription was shown to be induced by xylan, xylose, and beta-methylxyloside, and was repressed by the addition of 1% glucose. Glucose repression was partially relieved by addition of cAMP or dibutyryl cAMP.

β-Methyl-xyloside: positive effect on xylanase induction in Cellulomonas flavigena

Synthesis of extracellular xylanase in Cellulomonas flavigena is induced in the presence of xylan and sugarcane bagasse as substrates. The essential factors for efficient production of xylanase are the appropriate medium composition and an inducing substrate. The increase in xylanase production levels in C. flavigena were tested with a number of carbon sources and different culture conditions. Xylose, arabinose, glycerol and glucose did not induce xylanase production in this microorganism. beta-Methyl-xyloside (beta-mx), a structural analog of xylobiose, also did not induce xylanase when used as the sole carbon source, but when xylan or sugar cane bagasse was supplemented with beta-mx, extracellular xylanase production increased by 25 or 46%, respectively. The response of C. flavigena to xylan plus beta-mx was accompanied by a significant accumulation of reducing sugar, an effect not observed with the combination sugarcane bagasse plus beta-mx as substrate. To our knowledge, this is the first report on the effect of beta-mx on the induction of xylanase in C. flavigena.

Xylanases from fungi: properties and industrial applications

Xylan is the principal type of hemicellulose. It is a linear polymer of beta-D-xylopyranosyl units linked by (1-4) glycosidic bonds. In nature, the polysaccharide backbone may be added to 4-O-methyl-alpha-D-glucuronopyranosyl units, acetyl groups, alpha-L-arabinofuranosyl, etc., in variable proportions. An enzymatic complex is responsible for the hydrolysis of xylan, but the main enzymes involved are endo-1,4-beta-xylanase and beta-xylosidase. These enzymes are produced by fungi, bacteria, yeast, marine algae, protozoans, snails, crustaceans, insect, seeds, etc., but the principal commercial source is filamentous fungi. Recently, there has been much industrial interest in xylan and its hydrolytic enzymatic complex, as a supplement in animal feed, for the manufacture of bread, food and drinks, textiles, bleaching of cellulose pulp, ethanol and xylitol production. This review describes some properties of xylan and its metabolism, as well as the biochemical properties of xylanases and their commercial applications.

Production of amylase by Aspergillus fumigatus utilizing alpha-methyl-D-glycoside, a synthetic analogue of maltose, as substrate

A strain of Aspergillus fumigatus isolated from soil was able to produce biomass and high amylase activities in media containing alpha-methyl-D-glucoside (alphaMG), a synthetic analogue of maltose, as the only carbon source. alphaMG was a more effective inducer than starch and maltose at the same concentration: alphaMG cultures produced about 3 times more alpha-amylase and glucoamylase activity than starch cultures. Maximum production of alpha-amylase (60 U/mg) and glucoamylase (130 U/mg) was obtained in 8-10 days alphaMG cultures.

Carbon repression in Aspergilli

Many microorganisms prefer easily metabolizable carbon sources over alternative, less readily metabolized carbon sources. One of the mechanisms to achieve this is repression of the synthesis of enzymes related to catabolism of the alternative carbon sources, i.e. carbon repression. It is now clear that in Aspergillus nidulans and Aspergillus niger the repressor protein CREA plays a major role in carbon repression. CREA inhibits transcription of many target genes by binding to specific sequences in the promoter of these genes. Unfortunately there is little information on other components of the signalling pathway that triggers repression by CREA. In this review we summarize the current understanding of carbon repression in Aspergilli.

The use of methyl β-D-xyloside as a substrate for xylanase production by Aspergillus tamarii

Aspergillus tamarii was able to produce biomass in media containing β-methyl D-xyloside, a synthetic analogue of xylobiose, as the only carbon source. β-Methyl D-xyloside was a more effective inducer than xylan at the same concentration for xylanase and β-xylosidase activities. The delayed consumption of β-methyl D-xyloside by A. tamarii cells suggests the requirement of a specific inducible transport system and a slow metabolic process. The synthesis of this transport system was probably repressed by the presence of easily metabolizable sugars. β-Methyl D-xyloside was hydrolyzed to xylose by an intracellular β-xylosidase.Key words: xyanolytic microorganisms, xylanase, β-xylosidase, Aspergillus tamarii.