Abstract: The original strain Bacillus alcalophilus IS was mutated with ultraviolet(UV),diethl sulfate(DES) and UV plus DES. A mutant MS-UD2 was obtained,whose β-cyclodextrin glucanothansferase(CGTase) productivity was 2.96 folds as much as that of parent strain. The continuous 10 generations experiments showed that the mutant MS-UD2 is stable in CGTase production. The fermentation conditions for CGTase production were optimized via single-factor test and orthogonal test. The results showed that the optimal conditions are as follows:using fermentation medium consisting of maize powder 2%,corn steep liquor 6%,K2HPO4 0.15% and MgSO4·7H2O 0.02%,incubation temperature 28 ℃,amount of inoculum 8%,pH 10.0,filled medium volume in 250-ml flask 50 ml and adopting shaking incubation for 36 h at 180 r/min. The enzyme activity could reach as high as 5741.6 U/ml,under these conditions,and in 5-L fermentor the enzyme activity could reach 5920.0 U/ml.

Key words: Bacillus alcalophilus； &beta, -cyclodextrin glycanotransferase； strain breeding； fermentation condition optimization；