A newly isolated Bacillus subtilis JS-2004 strain was cultured in liquid media containing waste potato starch to produce alpha-amylase. The effect of calcium, yeast extract and glucose supplementation of the production medium on bacterial growth and enzyme production was studied. Maximum enzyme production 72 U/mL was achieved after 48 h cultivation at pH 7.0 and 50 degrees C. Addition of calcium and yeast extract enhanced microbial growth and enzyme production, where as glucose at 1.0% level showed a strong repression. Studies on crude alpha-amylase characterization revealed that optimum activity was at pH 8.0 and 70 degrees C. The enzyme was quite stable for I h at 60 and 70 degrees C, while at 80 and 90 degrees C, 12% and 48% of the original activities were lost, respectively. After incubation of crude enzyme solution for 24 h at pH 8.0 at 70 degrees C, a decrease of about 6% of its original activity was observed. The enzyme was activated by Ca2+ (relative activity 117%). It was strongly inhibited by Co2+, Cu2+, and Hg2+ but less affected by Mg2+, Zn2+, Ni2+, Fe2+, and Mn2+. The B. subtilis JS-2004 strain produced high levels of thermostable alpha-amylase with characteristics suitable for application in starch processing and food industries. (c) 2006 Elsevier Ltd. All rights reserved.