Study On Screening And Fermentation Conditions Of Xylanase Producing Strain

Xylanolytic enzymes, a system of hydrolytic enzymes, act cooperatively to convert xylan into its constituent sugars. Among these, xylanase (endo-β-1,4-D-xylanase) [EC3.2.1.8] plays a crucial role and has great potential applications in pulp and paper industry, food industry and feed industry etc. Since the demonstration that alki-treated wood pulp can be biologically bleached by xylanase instead of by the usual environmentally damaging chemical process such as chlorine, the research for thermostable alkaline xylanase has been extensive studied. In this paper, we carried out a series of experiments, including screening, identifying optimizing fermentation process, and studying characteristics of alkaline xylanase. The main results are as follows:1. A xylanase producing strain xy-7 was obtained from soil by assaying hydrolyzed circle on the selective medium and xylanase activity under shake-flask fermentation, in which xylan were used as the only carbon source. The xylanase activity under flask fermentation was 18.0 IU /mL. Based on its morphological, physiological and biochemical properties as well as the 16S rDNA sequence analysis result, strain xy-7 was tentatively identified as Paenibacillus campinasensis, which has never been reported among xylanase-production strains.2.Through a series of orthogonal experiments, effects of carbon source, nitrogen source and other factors on xylanase production from strain xy-7 were studied. The result shows that the optimal fermentation process for enzyme production were: 5% wheat bran, 0.7% corn steep, 0.5% yeast extract, 0.05% NaCl, 0.05% K2HPO4, 0.02% MgSO4·7H2O, pH 8.0 with 48h cultivation at 37℃. Under the optimized fermentation process, the xylanase production by strain xy-7 was increased from 18.0 IU/mL to 167.9 IU/mL.3 The study on characteristics of xylanase from strain xy-7 was carried out. The results show that the optimal reaction condition of xylanase was pH 7.0 at 60℃, respectively. The enzyme displayed good thermal stability, which remained 73% of intial activity after incubated for 2h at 60℃. At the same time, the xylanase remained higher activity over a range of pH 6.0 to 9.0, and its activity remained 68% of intial activity at pH 9.0. Compared with other reports about alkaline xylanases, the xylanase produced by strain xy-7 has some advantages on both thermostability and alkaline resistance. All these properties exhibited by the xylanase from strain xy-7 indicate that the enzyme is an alkaline xylanase.