Screening and identification of a strain with high yield of alkaline cellulase and its enzyme characterizations and fermentation conditions

【Objective】Strains with high yield of cellulase were isolated from the natural environment, and the enzymatic characteristics of screened alkaline cellulase were analyzed which could lay a foundation for the comprehensive development and utilization of the cellulase produced by this strain.【Method】The carboxymethyl cellulose sodium(CMC_Na) plate screening method was used to isolate and screen high yield cellulose-producing strains and then the isolated strains were identified by physiological and biochemical analysis and molecular biology method. The characteristics of enzyme activity and fermentation conditions were studied by 3, 5-dinitrosalicylic acid(DNS) method.【Result】Ahigh alkaline cellulase producing strain was isolated from the soil samples which were long-term covered by rotting leaves and this strain was identified and named as Bacillus cereus strain CQNUX 3-1. The results of enzyme activity tests showed that strain CQNUX 3-1 exhibited the activity of endoglucanase, exoglucanase and β-glucosidase and were 107.7, 33.1 and 155.6 U/mL, respectively. Analysis of enzymatic characterization showed that the three enzymes had better alkaline resistance and certain high temperature performance. The optimum reaction temperature of endoglucanase, exoglucanase and β-glucosidase were 70, 60 and 40℃, respectively. The best reaction pH were 8.0, 9.0 and 9.0 respectively. Fe³⁺ could increase the enzyme activity of three enzymes, while β-glucosidase showed better tolerance to EDTA, urea and Cu²⁺. The effect of fermentation conditions on the enzyme production showed that the optimum fermentation temperature of the strain was 37℃and the enzyme activity could reach to the maximum after four days fermentation. Finally, the bacteria could grow and produce enzymes under alkaline fermentation environment. Enzyme activity was the best when the initial pH was 7.0.【Conclusion】A strain with high alkaline cellulase producing is selected. The cellulase produced by B. cereus strain CQNUX 3-1 has high reaction temperature applicability and strong alkali resistance. The strain fermentation enzyme has moderate temperature and has a wide range of fermentation pH. This strain can be used as a alkaline cellulase production resource strain, with the potential for the preparation and production of cellulase preparations and the comprehensive utilization of cellulose resources.