The Screening Of Xylanase-producing Bacterias And Studies On Enzymetic Property

Xylanases can hydrolyze hemicelluloses, which are the second abundance renewable resource. Xylanases have a broad prospect in food industry, paper industry, animal feed industry and energy bioconversion etc. This study carried out a series of experiments: screening, identification, properties of xylanase and the optimal culture conditions for high production. A high xylanase-producing Paenibacillus.sp was first isolated from the soilsamples and identified. The main results are follows:According to xylan-hydrolyzed halos method, the ingredients of the medium for screening of xylanase-producing strain in this study included self-made corncob xylan and birchwood xylan, respectively. With this method, the sizes and transparency of transparent zones surrounding colonies in Petri dishes were directly proportionate to their xylanase activities. 30 xylanase-producing strains were screened from the soil-samples which full of high hemicellulose. L0302, L0602 and L0604 strains presenting the higher activity were selected for further investigation by experiments in shake flasks. According to the morphology, cultural characters, physiological and biochemical characteristics and analysis of 16SrRNA sequence, three strains were all identified as Pacnibacillus.sp. the xylanase activities of them were 110.79U, 118.22U and 117.94U. respectively. L0604 was ultimately selected as a candidate due to its most prominent xylanase activity.Based on the study of xylanase. the enzymetic properties of crude enzyme were discussed. The crude xylanase of L0604 strain displayed an optimal pH at 5.0 and optimal temperature at 50℃. It was stable at pH5.0. And has a wide stable pH range from 4.0 to 10.0. At this situation. it still had 80% activity, and still had 80% activity. It kept stable at 40℃, The activity of xylanase at this temperature was observed increased with increasing the time of incubation. After incubated for 60 min at the temperature range from 20℃to 50℃, it still had 88% activity. In the metal ions investigated. Cu²⁺, Zn²⁺,Mg²⁺ promoted effects on xylanase, and the activity of xylanase was increased with increasing the concentration of these metal ions in certain does. The other ions all inhabited its activity more or less. Especially, Cu²⁺ promoted 150% activity in the enzyme reaction.After single factor tests and orthogonal array, the best condition for L0604 strain produce xylanase were corncob xylan used as carbon source and tryptone as nitrogen source. The optimal medium was consisted of corncob xylan 3.0%, tryptone 0.6%. K₂HPO₄ 0.5%, tween80 0.4%.the initial pH of medium was 7.0. Shaken at 220r/min and cultured in this optimal medium for about 96 hours at 32℃, the xylanase activity was up to 194.67U, which was 1.58 times of original enzyme activity.