A new strain of Bacillus sp. I-3, isolated from natural soil samples, showed a high raw starch digesting activity towards potato starch. Upon optimization of various environmental and cultural conditions, the yield of alpha-amylase reached 642 U/mL. The kinetic characterization of partially purified enzyme exhibited the maximum activity at 70 degrees C, pH 7.0 and revealed a high thermostability in the presence of 10 mM CaCl(2)center dot 2H(2)O where it could retain more than 90% residual activity at 70 degrees C after 3.5 It. At 80, 90 and 100 degrees C, the enzyme retained 80, 59 and 26% of its maximum activity after 2.5, 0.5 and 0.5 h, respectively. The enzyme preparation had a strong affinity towards raw potato starch granules and was almost completely adsorbed onto it. It also hydrolyzed raw potato starch at a concentration of 12.5% significantly in a short period of time of 12 h. (c) 2005 Elsevier Inc. All rights reserved.