The Basic Study On The Xylanase From Alkalophilic Bacteria And Its Application

Alkalophilic bacteria are a kind of novel microorganism resources, they have an important theory and application value in the gene engineering and the industrial production due to their unique tolerant ability for high pH. Alkalophilic bacteria and their alkaline extracellular enzymes can degrade the noncellulosic constituents of plant fiber as pectin and hemicellulose, and have the compatibility with the alkaline conditions in the traditional plant fiber processing. Therefore, they have vast application prospects in the pulp, papermaking and bast fiber textile industry. If the cellulosic materials are pretreated by biopulping, biobleaching and biodegumming with alkalophilic bacteria and their extracellular enzymes, the chemical charge may be obviously reduced in the following processes, so the energy consumption and the environmental pollution may be decreased effectively. Therefore, it has the vital significance to the social economy sustainable development.In this study, a strain with higher xylanase activity was selected from 78 strains of alkalophilic bacteria, and the condition for the enzyme production was optimized. Meanwhile, the preliminary study to this enzyme characteristic was conducted, and the feasibility of bast fiber biodegumming with the strain was discussed. The main contents and conclusions are as follows:1. A xylanase producing alkalophilic Bacillus NT-16 was screened, and the effects of culture time, carbon source, nitrogen source and Tween-80 on the enzyme production were studied. The results show that the hemicellulose was the optimum carbon source, and the pancreas-poptone was the optimum nitrogen source. The optimal condition for the enzyme production was hemicellulose 2%, pancreas-poptone 1%, Tween-80 0.1%, K₂HPO₄ 0.1%, MgSO₄·7H₂O 0.02%, Na₂CO₃ 1%, with 72 h cultivation 37°C. Under such a condition, the enzyme activity can reach 12.24 IU/ml.2. To do the groundwork for industrial application, the xylanase produced by alkalophilic Bacillus NT-16 was separated by fractional precipitation with ammonium sulfate, and the effects of the temperature, pH and metal ions on the activity of xylanase were discussed. The results show that the xylanase was purified by the fractional precipitation, the recovery was 80%, and a 2.11-fold-purification was achieved. The enzyme has a better thermostability at temperature below 55°C and high activity from pII 7.0 to pII 11.0. The enzyme has a pH optimum of pII 9.0. so it...