Production of alpha amylase using amplified variants of Bacillus subtilis (strain SCH) and of Bacillus amyloliquefaciens (strain 267CH) was conducted in a bioreactor with multiprotein-mineral media. The time course of fermentation in a bioreactor revealed that the highest yield (about 8 x 10⁴ U/ml within 60 h) by strain SCH was obtained by applying: 3.5% initial starch, 2% additional starch after 19 h, 3 vvm aeration and 300 rpm agitation. The highest yield (about 19 x 10⁴ U/ml within 100 h) by strain 267CH was obtained by applying: 2.5% initial starch, 2% additional starch after 24 h, 3 vvm aeration, and 300 rpm agitation with the productivity after 60 h reaching only about 14 x 10⁴ U/ml. Production occurred in both the logarithmic and postlogarithmic phases of growth. Maximum consumption of starch and protein occurred during the first day of incubation. The optical density peak coincided with enzyme production peak in case of strain SCH and preceded that of enzyme production in case of strain 267CH. The alpha amylase produced by the two strains was shown to be of the liquefying and not the saccharifying type. Both enzymes liquefied starch to a dextrose equivalent of about 15 - 17 at 95^oC hence they are classified among thermostable alpha amylases. They exhibited broad pH and temperature activity profiles. The optimum pH for activity was 4 - 7 for alpha amylase produced by strain SCH and 4 - 8 for alpha amylase produced by strain 267CH while the optimum temperatures for their activities were in the range 37 -75^oC at 0.5% starch and in the range 85 - 95^oC at 35% starch.

Key words: Production kinetics, process modeling, fermentation, bacterial amylase, biotechnology.