Screening And Identification Of A Xylanase-producing Strain And Purification Of The Xylanase

Biomass is abundance in our country.Transforming biomass into energy through biological way is clean and renewable which can substitute part of fossil energy and reduce the releasing of the green house gas.The transformation of biomass energy is mainly composed of the two crucial steps which are biomass decomposition and biomass transformation.In the decomposing stage how to improve the decomposing efficiency of hemicellulose is the key point,thus screening and cultivation of high efficient strains is of great importance for the exploiture and utilization of hemicelluiose.Six hemicellulose-decomposing strains were isolated from the refuse soil samples using bagasse hemicellulose as the sole carbon.The strain with high xylanase activity was observed through contrasting xylanase from solid-ferment bagasse.The micro-morphology of mycelia and spores of the strain were observed.The results showed that its morphological characteristics possessed of that of Aspergillus sp.The result of analysis of 18S rDNA sequences of the strain showed 97%similarity to Aspergillus sp.The strain was identified as Aspergillus sp.HQ3 by the result of analysis of 18S rDNA sequences and phenotypic properties.The optimum solid-state fermentation conditions for xylanase production were obtained as:bagasse:bran=7:3(W/W),solid:liquid=1:4(W/W),urea 0.4%,pH 7.0, fermentation temperature 30℃,fermentation time 4 d.The activity of xylanase reached 3421 U/g koji under the optimum conditions.For obtaining the high xylanase-producing strain,this study focuses on the purification of the xylanase and analysis of the enzymology character of the xylanase from Aspergillus sp.HQ3.The(NH₄)SO₄ was added to the culture filtrate,and the precipitated material was collected by centrifugation.The xylanase was purified by Phenyl Sepharose 6 Fast Flow(High Sub) chromatography and Sephadex S-200 chromatography.Its recovery rate and purification fold were respectively 1%and 5.7. SDS-PAGE showed that molecular weight of the xylanase was 33 kD.The result of enzymology character analysis was that the optimal pH was 4.8 and the optimal temperature was 50℃.