Isolation,Identification and Enzyme Properties of a β-Mannanase Producing Strain with High Thermal Stability

To develop a thermostable β-mannanase,a high β-mannanase producing strain was isolated from soil based on the sole carbon source cultivation and clearing zone screening on konjac powder plates. The strain was identified by 16S rDNA phylogenetic analysis. The β-mannanase activity and the enzyme properties were assayed by DNS method. The results showed that the strain could hydrolyze konjac powder and the clearing zone D/d value was about 1.67. The strain was assigned to Bacillus licheniformis KD-1.The optimal pH of the enzyme was pH6.0 and the optimal temperature was 60℃. The β-mannanase was stable at pH5.0~9.0 and 60~80℃. The half-life time(T1/2)of the enzyme activity was 5.5,4.3 and 4.2 h at 60,70 and 80℃. The β-mannanase activity was promoted by 10 mmol/L Cu²⁺ and Mg²⁺,whereas the enzyme activity was inhibited by 10 mmol/L Mn²⁺. In this study,a strain of Bacillus licheniformis KD-1 was screened. The thermostability of β-mannanase produced by KD-1 was higher than that of β-mannanase reported at present.