Purification and medium optimization of α-amylase from Bacillus subtilis 168

alpha-Amylase was first time isolated and purified from Bacillus subtilis 168 (1A1). Purified alpha-amylase fraction showed a single protein band with a molecular weight of 55 kD. Chemical characterization of the purified alpha-amylase revealed optimum amylolytic activity at 37 degrees C and pH 7.0 using starch as substrate. It was stable at pH 5.0 to 9.0 and at temperatures 25-70 degrees C. Culture conditions were optimized by using statistics-based experimental designs to enhanced alpha-amylase (EC.3.2.1.1) production. A two level fractional factorial Plackett-Burman design was used for the preliminary screening significant media components and conditions. Response surface methodology (RSM) involving a 2(4) full-factorial central composite design (CCD) and a second-order polynomial equation was then employed to identify the relationship between the alpha-amylase yield and the four significant variables. Optimal levels of the significant variables for the maximum alpha-amylase yield were starch 2.55 g/l, yeast extract 8.4 g/l, sodium chloride 8.1% and 48 h of incubation. Mean value of alpha-amylase yield was 639.7 IU/ml, which was in excellent agreement with the predicted value (633.5 IU/ml).