Straw Pulp Using Xylanase Production Strain Screening, Purification And Application Effect

Since the first report that the use of xylanase in pulp bleaching could dramatically reduce the amount of chemical bleaching reagents in 1986, scientists all over the world have done lots of related research. In China, wheat straw is the main resource of pulp industry. Conventional pulpmaking and bleaching techniques have brought severe environmental pollution. Researchers in our country have also done lots of work referencing to this area. A lot of microbes, which can produce xylanase, have been isolated. Our laboratory also isolated Aspergillus niger An76 and Bacillus pumilus A30 et ah from nature. At present, the main problem is that xylanse from fungi was not alkalophilic and xylanse from bacteria improved wheat straw pulp brightness unconspicuously. So it is most important of isolating alkalophilic fungi that produce xylanase and using it in the paper industry. Perhaps this can accelerate the development of paper industry in our country.In this paper, lots of alkalophilic and neutrophilic microorganism, Which produce xylanase, were isolated from alkaline soil. Four of them that exhibited high activities of xylanase were obtained. By comparing to enhanced effectiveness of bleaching in xylanase-boosted bleaching of wheat straw pulp with the xylanase, fungus ZCF57 was screened out and preliminarily identified as Pemcillium. The optimum pH and temperature for crude xylanase from ZCF57 was 7.0 and 55℃, respectively. It was stable in the range of pH5.0-10.0 and below 45℃. Some of transition metal ions, such as Fe2+, Mn~2+ and Mg2+ can increase xylanase activity of ZCF57 dramatically.The culture conditions for producing xylanase were optimized by shaking flask liquid fermentation, and the optimal conditions are as follows: initial pH9.0, 32℃ and shaken at 150 rpm for 72h. The 3% of corncob powder and 1% of soybean cake powder was used as optimum carbon source and nitrogen source, respecitively. The highest xylanase activity was above 550 IU/ml under the optimum conditions of cultivation. When ZCF57 cultured in the optimized conditions, the xylanase activity is increased by 4 times.The crude culture filtration of ZCF57 was purified by ammonium sulfate fractionation, Sephadex G-100 and DEAE-Sephadex A-50 chromatographies, and two pure enzyme, XIand XII were obtained. It was indicated that the molecular weights of XIand Xllare 23kD and 16kD by SDS-PAGE analysis. As far as the enzyme activity is concerned, the optimum temperature and pH was 55℃ and pH 7.0 for the enzyme XI, and 50℃ and pH 6.0 for the enzyme XII, respectively. It was stable in the conditions of below 45℃ and pH 6.0~9.0 for enzyme XIand of below 50℃ and pH5.0~8.0 for enzyme XIIXylanse ZCF57 from the crude culture filtration of fungus ZCF57 was used for pretreating wheat straw pulp prior to bleaching to investigate effectiveness of enhanced bleaching with the xylanase. Results of the experiments showed that the brightness of pulps could be increased about 3~4 % ISO with a dose of 10 IU xylanase per gram pulp of oven dry weight, indicating that it was feasible for improving bleaching effectiveness of wheat straw pulp using xylanase of ZCF57.