Optimization of xylanase production from Aspergillus niger for biobleaching of eucalyptus pulp

A crude endo-xylanase produced by Aspergillus niger BCC14405 was investigated for its potential in pre-bleaching of chemical pulp from eucalyptus. The optimal fermentation conditions on the basis of optimization using response surface methodology included cultivation in a complex medium comprising wheat bran, rice bran, and soybean meal supplemented with yeast extract, glucose, peptone, and lactose with a starting pH of 6.0 for 7 d. This resulted in production of 89.5 IU/mL of xylanase with minor cellulase activity. Proteomic analysis using LC/MS/MS revealed that the crude enzyme was a composite of hemicellulolytic enzymes, including endo-β-1,4-xylanase and other hemicellulolytic enzymes attacking arabinoxylan and mannan. Pretreatment of the pulp at a xylanase dosage of 10 IU/g increased the brightness ceiling after the C-Eop-H bleaching step up to 3.0% using a chlorine charge with a C-factor of 0.16-0.20. Xylanase treatment also led to reduction in chlorine charge of at least 20%, with an acceptable brightness level. The enzyme pretreatment resulted in a slight increase in pulp viscosity, suggesting an increase in relative cellulose content. The crude enzyme was potent in the enzyme-aided bleaching of chemical pulp in an environmentally friendly pulping process.

Medium- to large-sized xylo-oligosaccharides are responsible for xylanase induction in Prevotella bryantii B14

Experiments were done to define the nature of the xylan-derived induction signal for xylanase activity, and evaluate which xylanase genes among the three known ones (xynA, xynB and xynC) are induced by the presence of xylan in Prevotella bryantii B(1)4. During the later stages of exponential growth on glucose, addition of 0.05 % water-soluble xylan (WS-X) stimulated xylanase formation within 30 min. Xylose, xylobiose, xylotriose, xylotetraose, xylopentaose, arabinose and glucuronic acid all failed to induce the xylanase activity. An acid-ethanol-soluble fraction of WS-X (approximate degree of polymerization 30) enhanced the activity significantly, whereas the acid-ethanol-insoluble fraction had no effect, unless first digested by the cloned P. bryantii XynC xylanase. These results indicate that medium- to large-sized xylo-oligosaccharides are responsible for induction. The transcription of all three known xylanase genes from P. bryantii was upregulated coordinately by addition of WS-X. There have been relatively few investigations into the regulation of xylanase activity in bacteria, and it appears to be unique that medium- to large-sized xylo-oligosaccharides are responsible for induction.

Preparation and preliminary X-ray analysis of the catalytic module of beta-1,3-xylanase from the marine bacterium Vibrio sp. AX-4

Beta-1,3-xylanase (1,3-beta-D-xylan xylanohydrolase; EC 3.2.1.32) is an enzyme capable of hydrolyzing beta-1,3-xylan. The newly cloned beta-1,3-xylanase from the marine bacterium Vibrio sp. AX-4 (XYL4) exhibited a modular structure consisting of three modules: an N-terminal catalytic module belonging to glycoside hydrolase family 26 and two C-terminal xylan-binding modules belonging to carbohydrate-binding module family 31. Despite substantial crystallization screening, crystallization of the recombinant XYL4 was not accomplished. However, the deletion mutant of XYL4, composed of a catalytic module without a xylan-binding module, was crystallized. The crystal belonged to space group P2(1)2(1)2(1), with unit-cell parameters a = 51.6, b = 75.8, c = 82.0 A. X-ray diffraction data were collected to 1.44 A resolution.