Purification and biochemical characterization of a thermostable and acid-stable alpha-amylase from Bacillus licheniformis B4-423

Novel thermostable amylase need to be continuously explored with the improvement of industrial requirements. A new acidophilic and thermostable amylase producing bacterium isolated from spring was identified as Bacillus strain on the basis of 16S rDNA. The amylase was purified by ammonium sulphate precipitation, gel chromatography and anion exchange chromatography. SDS-PAGE revealed that the enzyme was monomeric with a molecular weight of 58 kDa. The amylase exhibited optimal activity at pH 5.0 and temperature 100 °C. Then the enzyme showed high stability in pH ranges 4.0-10.0 and more than 90% of maximal activity was found from 20 °C to 80 °C. Apart from good stability toward SDS and non-ionic detergent, the purified enzyme exhibited high compatibility with some inhibitors such as urea and EDTA. The results demonstrated the stability of the enzyme in different organic solvents. Moreover, we determined the amylase gene, compared the structure with α-amylase BAA and BLA and found some thermostability determinants in our enzyme. Overall, presenting various properties were including high thermostability, Ca2+-independency, broad temperature and pH profiles, organic-solvent tolerance as well as excellent stability with detergents. Such characteristics have not been reported for this type of enzyme, and the α-amylase will be a suitable candidate in industrial fields.