产碱性木聚糖酶菌株的筛选及酶学性质

从青海盐碱湖土壤中筛选到25株产碱性木聚糖酶的菌株, 其中编号为QH14的菌株产酶量达648.79 U/mL, 纯化后比活可达1148.56 U/mg。16 SrDNA鉴定表明菌株QH14属于短小芽孢杆菌, 命名为Bacillus sp. QH14。从该菌株的基因组中克隆获得了碱性木聚糖酶编码基因XynQH14, 并在大肠杆菌E.coliBL21(DE3)中获得重组表达。通过Ni-NTA亲和层析分离纯化后的重组QH14木聚糖酶比活达700.47 U/mg。该碱性木聚糖酶的酶促反应最适温度为60℃, 最适pH为9.2; 55℃处理1h仍保持50%的活力; 在pH7.0~11条件下37℃处理酶液24 h后均保持80%以上的活力, 且在pH11缓冲溶液中50℃处理24 h仍保持31.02%的酶活, 显示了该碱性木聚糖酶较好的热稳定性和碱稳定, 提示该碱性木聚糖酶在制浆造纸、纺织等行业的应用潜力。

Isolation and characterization of an alkaline xylanasefrom a newly isolated Bacillus sp. QH14

Twenty-fivealkaline xylanase producing strains were isolated from Qinghai Lake side soil samples. Among these strains, QH14 produced 648.79 U/mLxylanase, and the enzymatic specific activity was 1148.56 U/mg after purification. This alkaline xylanase producing strain belongs to genus Bacillus based on16S rDNA sequencing analysis and then was designated as Bacillus sp. QH14. The alkalinexylanaseencoding gene, XynQH14, was cloned from Bacillus sp. QH14 and expressed in Escherichiacoli BL21 (DE3). The specific activity of the recombinant xylanase XynQH14 was 700.47 Umg^-1 after purification by Ni-NTA affinity chromatography. The optimal tempera-ture and pH of XynQH14 were 60℃ and pH9.2, respectively. Its activity was 50% of initial activity after incubation at 55 ℃ for 1h, 80% at pH7-11 at 37 ℃ for 24 h, and 31.02% at pH11 at 50℃ after 24 h, indicating that XynQH14 isthermosta-ble and alkali-stable. These properties ofXynQH14 suggest its favorable potential applications in pulp and paper industries.