Production, Purification and Partial Characterization of Moderately Thermostable β-Amylase from Bacillus polymyxa BWB-01

摘要

Despite the higher activity possessed by bacterial p-amylases, plant p-amylases are widely used for industrial processes. It is crucial that targeted improvements must be made on bacterial β-amylases for enhanced production, thermal and operational stability for their commercial viability. In this study, Bacillus polymyxa BWB-01 was cultivated in submerged fermentation and influence of cultivation conditions (pH,temperature, carbon and nitrogen sources) on β-amylase production was investigated. β-amylase was purified in a three-step procedure before characterization. Maximum p-amylase production (75.88 U/ml) was obtained at pH 6.0 and 40 °C with soluble starch and malt extract as carbon and nitrogen sources. β-amylase was purified 5.64-fold with 19% yield. The purified enzyme had optimum activity at 50 °C and pH 6.0, and exhibited remarkable stability over broad pH range (4.0-8.0) after 60 min incubation having residual activity of about 90% at dH 7.0. 6.0 and dH 5.0 with 50% residual activity at pH 4.0 and 8.0, respectively. The purified β-amylase uniquely retained 80% and 73% of its.original activity after prolonged incubation (180 min) at pH 6.0 and 5.0,and still had residual activity of 65% after 300 min. The enzyme was moderately thermostable exhibiting 62% residual activity after 60 min at 50 °C and 54% at 60°C after 30 min. p-amylase activity was enhanced by Mn~(2+) and Fe~(2+) but completely inhibited by Cu~(2+). B. polymyxa BWB-01 is a good producer of p-amylase with improved characteristics for application in food industry.