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Lignocellulose is the most abundant bio-energy resource in the world. It is believed that making full use of bio-energy can relieve the problem of the inadequacy of energy resources and environmental pollution in the whole world. The key element in bio-energy technique is to find novel and high activity lignocellulases. To achieve this goal, we explored the gene resources in yak rumen microorganisms by means of metagenomic.In the present study, a novel gene, RuCelA, encoding a bifunctional xylanase/endoglucanase, was cloned from a metagenomic library of yak rumen microorganisms. RuCelA showed activity against xylan and carboxymethylcellulose (CMC), suggesting its bifunctional xylanase/endoglucanase activity. The optimal temperatures for xylanase and endoglucanase activities were 65℃and 50℃, respectively. RuCelA displayed a pH optimum of 5.0 and 7.0 for its endoglucanase and xylanase activity, respectively. The presence of Co+ and Co2+ can greatly improve RuCelA’s endoglucanase activity while inhibiting its xylanase activity. Product analysis showed RuCelA’s endoglucanase and xylanase activity both functioned through endo-mode, producing maily disaccharide, trisaccharide, and tetrasaccharide, with a small quantity of monosaccharide. RuCelA could degrade cellotetrose into glucose, cellobiose, and cellotriose. Further examination of substrate preference showed higher activities against substrates with mixedβ-1,3/4 linkages like barley glucan and lichenin than against xylan and CMC, and RuCelA can not degrade substrates withoutβ-1,4 linkages likeβ-1,3 glucan and laminary. RuCelA also showed activity towards filter paper and methylumbelliferyl-β-D-cellobioside (MUC), an aryl-scaffolded trisaccharide mimic. Using xylan and barley glucan as substrates, RuCelA displayed obvious synergistic effects withβ-1,4-xylosidase andβ-1,4-glucosidase. It is greatly notable that RuCelA can continually hydrolyze pretreated rice straw at 45℃for 2 weeks. Therefore, RuCelA, bifunctional and pH tolerant as well as highly stable, distinguishes itself as an ideal candidate for industrial applications such as the production of bio-ethanol from straw. And we also constructed engineering strains in Pichia pastoris which produced high level of recombinant proteins.
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