Screening , identification and fermentation optimization of xylanase - producing endophytic bacteria from Cymbidium faberi Roots

Xylanases have raised interest because of their potential applications in various industrial fields. In this paper, a high-efficiency xylanase - producing strain 6hRe76 was screened from 592 Cymbidium faberi endophytic bacteria. The fermentation conditions for xylanase production were optimized by Response Surface Methodology (RSM). In the first, one factor experiment was used to screen the best carbon source and nitrogen source. The results showed that wheat bran and yeast extract was as the optimum carbon source and nitrogen source, respectively.   Secondly, Wheat bran, K₂HPO₄ and liquid volume were certified as the major factors influenced xylanase production by Plackett-Burma experiment. The optimal conditions were wheat bran 5.6%, K₂HPO₄ 0.685% and liquid volume 10.5/50mL through steepest ascent experiment. Then, Box-Behnken method was used in response surface experimental design, and experimental data were analyzed by using Minitab software. The response surface mode constructed indicated that the optimal conditions for xylanase production by strain 6hRe76 were as followingFinitial pH9.0, 34°C, ,liquid volume 10.92/50 mL and shaken at 180 rpm for 36 h, and the optimal medium components were wheat bran 5.92%, yeast extract 0.75%, K₂HPO₄ 0.71%, MgSO₄ 0.05%, CaCl₂ 0.05% and Tween80 0.15%. The studies on crude enzymatic properties showed that its optimum reaction temperature and pH were 50°C and 7.0, respectively.Under the optimal conditions,the maximum activity of xylanase was 105 U/mL. Based on morphological, physiological and phylogenetic data, strain 6hRe76 was identified as Paenibacillus kribbensis.