Pure Xylan Research Articles

Production of xylanolytic enzymes during growth on pulverized grass by Aspergillus ochraceus-42

Xylanase and β‐xylosidase with activity of 6.46 U mg‐1 and 0.500 U mg‐1, respectively, were produced extracellularly by Aspergillus ochraceus during growth on pulverized grass in liquid state fermentation, compared to 9.3 U mg‐1 and 0.74 U mg‐1 when pure xylan was used. The culture filtrate was devoid of any cellulase activity. Xylanolytic enzymes were produced optimally in 144 h of incubation on 1% pulverized grass, pH 6.5. About 8.43% (w/w) sugars were liberated from alkali‐treated grass in 6 h by the synergistic effect of xylanolytic enzymes. The half‐lives for xylanase and β‐xylosidase at 50°C were 210 min and 300 min, respectively, and half‐life increased with the increase in protein concentration. Both mono‐ and divalent cations, especially K+ and Zn2+, exhibited a profound effect on the rate of enzyme saccharification.

Formation of xylanase by Schizophyllum commune: Effect of medium components

Growth of a wild strain of Schizophyllum commune on cellulose or cellulose-rich substrates in submerged culture resulted in the production of cellulase, xylanase, and mannanase activities. Pure xylan or galactomannan as carbon sources did not specifically induce the formation of xylanase or mannanase, respectively. Production of cellulase, xylanase, and mannanase activities decreased with an increasing ratio of xylan to cellulose, or mannan to cellulose, in the growth medium. During growth experiments, formation of xylanase, cellulase, as well as mannanase was induced not only by cellulose, but also by cellobiose, lactose, and l-sorbose. Xylans from birchwood, xylose, and β-methyl- d-xyloside, a structural analogue of xylobiose, did not induce xylanase formation when employed as substrates. These results indicate that the synthesis of xylanase, cellulase, and mannanase activities is likely to be under common regulatory control in the case of Schizophyllum commune. The inducer seems to be a small molecule derived from cellulose. Constitutive levels of xylanase and cellulase activities were detected during growth of the fungus on easily metabolizable substrates such as glucose, xylose, or glycerol. Among various organic nitrogen sources tested, yeast extract was found to be optimal for the production of xylanase.

High activity xylanase from Aspergillus sydowii MG49 during growth on jute stalk lignocellulose

Aspergillus sydowil MG49 produced 33.0 U mg-1 of extracellular xylanase activity when grown in liquid state fermeniation (LSF) with 1% ground jute stalk as the sole carbon source compared to 56.0 U mg-1 when pure xylan was used. Optimum time-course and pH for maximum enzyme production were 144 h and 4.0 respectively. The culture filtrate was devoid of any cellulase and β-xylosidase activity. The xylanase exhibited optimum activity at 60°C and pH 5.5. Partially-fermented jute stalk could be recycled at least twice for xylanase production, exhibiting 25.8 and 17.4 U mg-1 activity in two later consecutive cycles respectively.

Physiological studies on xylanase production by Penicillium funiculosum on some agricultural wastes

Studies were carried out on production of Xylanase enzyme from P. funiculosum NRCE-629 using a number of alkali-treated lignocellulosic wastes as carbon and energy sources as compared to pure xylan polymer. Sugar cane bagasse, rice straw and wheat straw yielded enzyme levels higher than that obtained on pure xylan. Physiological studies on enzyme formation using those three agricultural wastes revealed that optimum enzyme yields are obtained in media containing 2% substrate concentration. The enzyme synthesis was favored in agitated cultures with an air:medium ratio corresponding to 3:2 respectively with inoculum size of 10% (v/v). Further studies using rice straw medium yielded highest enzyme level after five days of aerobic growth at 30 degrees C with initial pH of medium adjusted to 5.0. Results are discussed in the light of possible application.

High activity xylanase from thermotolerantStreptomyces T7: Cultural conditions and enzyme properties

A thermotolerantStreptomyces T7 produced 70–72 U/ml of extracellular xylanase activity when grown at 50°C in submerged culture, in a medium containing 5% wheat bran as a carbon source. Among the various sugars tested, maltose showed the highest activity of 8 U/ml. Pure xylan was less effective as an inducer as compared to wheat bran. Ammonium sulphate at a concentration of 0.7% was found to be optimum for maximum yield of the enzyme. The optimum period and pH for maximum production were 72th and 7.0, respectively. The culture filtrate was devoid of amylase, cellulase and B-xylosidase activity. The xylanase was exceptionally stable and did not show any loss in activity after storage at 50°C at pH 5.0 for 6 days.

Xylanase production by Trichoderma longibrachiatum

The effects of carbon source, substrate concentration, culture pH, and spore inoculum concentration on production of extracellular xylanase and cellulase were examined. Very low enzyme activities were obtained with growth on glucose, xylose, and cellobiose, while significantly higher levels were produced from lactose and arabinose. Higher levels of both enzymes were generated from alpha cellulose, wood pulp, and fibrous paper waste than from purified xylan. However, the ratio of xylanase to cellulase activity was higher with pure xylan. High levels of both xylanase and cellulase activity were obtained when the culture was grown on lactose plus xylan. A factorial experiment showed that spore and substrate concentration had significant effects on xylanase yield, and that an interaction existed between these two variables. Highest levels of xylanase were generated with cultures grown on 1% wood pulp at pH 7.0 using an inoculum of 10 5 spores ml -1. Maximal xylanase activity was observed at pH 4.8-5.5 at 55°C using a 30-min assay. The type of xylan used as substrate and the method of reducing sugar detection significantly affected measured xylanase activity.

Biosynthesis of pure araban and xylan

A crude particulate enzyme preparation from mung bean shoots partially freed from sugar transferases synthesized pure araban from UDP- l- 14C-arabinose. The preparation thus allowed to study some properties of the UDP-arabinose transferase which was shown to require 7 mM Mn 2+ and pH 6–6·5 for optimal activity. Pure xylan was synthesized from UDP- d- 14C-xylose if a mixture of 0·06% Triton X100 and 35 mM EDTA was added to the crude enzyme preparation. In contrast to the UDP-arabinose transferase the UDP-xylose transferase does not require bivalent metal ions.

Studies on the Xylan of Various Straws

Conditions for separating xylan from straws were examined to obtain an industrial raw material for enzymatic production of xylose. Following procedure was found to be most effective with 90% recovery of xylan. Thus, straw was soaked in 2% NH4OH for 24hrs. at room temperature, in 10% NaOH at 50-60°C for 48hrs., and then filtered. Xylan was precipitated by adding two parts of methanol to one part of the filtrate, and dried under reduced pressure. Crude preparations obtained by this procedure from rice straw (A), bagasse (B), wheat straw (C), and barley straw (D) contained 54.3, 73.5, 73.6, and 76.8%, respectively, of pure xylan determined by Tollens-Krober's method. According to gas chromatography of their acetylated hydrolyzates of those preparations, molar ratio of pentoses of xylans were as follows; xylose 81.7: arabinose 17.6: rhamnose 0.7 for (A), 84.0:15.1:0.9 for (B), 87.5:12.4:0.1 for (C), and 84.1:15.4:0.5 for (D).

CRYSTALLINE XYLANS FROM STRAWS

Hemicelluloses, extracted from barley, flax, oat, rye, and wheat straw holo-celluloses, were composed predominantly of anhydro-D-xylose units, with small amounts of L-arabinose and D-glucuronic acid. The hemicelluloses had degrees of polymerization ranging from 55 for oat to 185 for rye and were shown to be linear polysaccharides. Autoclaving in distilled water at 120 °C. yielded crystalline xylans from barley, rye, and wheat straw hemicelluloses. The basic structure of the hemicellulose was maintained in the crystalline xylans, which gave identical X-ray diffraction patterns and had similar, linear structures. The crystallization procedure was found to degrade the hemicellulose, removing D-xylose, L-arabinose, and D-glucuronic acid as components of hydrolytic fragments and leaving a pure xylan one sixth to one third the length of its parent hemicellulose. Depending on uronic acid content, the five hemicelluloses in water gave pH values ranging from 2–5 with consequent variations in resistance to hydrolysis during autoclaving