Optimization of medium constituents and process conditions for alkaline α-amylase production by B. subtilis. Histogram: alkaline α-amylase activity; Black dot: dry cell weight (DCW). a: Effect of starch on the recombinant α-alkaline amylase production by B. subtilis. Different concentrations of starch added into the medium were 0, 0.6, 1.2, 1.8, 2.4, 3.0, 3.6 and 4.2% (w/v). b: Effect of peptone concentrations on the recombinant production of α-alkaline amylase by B. subtilis. The different concentrations of peptone were 0.45, 0.95, 1.45, 1.95, 2.45, 2.95, 3.45 and 3.95% (w/v). c: Effect of soybean meal concentrations on the α-alkaline amylase production by B. subtilis. The different concentrations of soybean meal were 0, 0.3, 0.8, 1.3, 1.8, 2.3 and 2.8% (w/v). d: Effect of temperature on the recombinant α-alkaline amylase production by B. subtilis. The different temperatures were 25, 28, 31, 34, 37 and 40°C.