Effect of metal ions and different carbon and nitrogen sources on amylase activity. (A) The relative enzyme activities were measured at optimum of pH and temperature and enzyme activity without metal ions was taken as 100%. (B) Effects of different carbon and nitrogen sources at optimum conditions (25°C and pH 9) on α-amylase production of P. minima. The hydrolase-inducing medium of Nyugen et al.  was used as a control. Where nitrogen sources were replaced, starch was the carbon source (as per the control medium); where carbon sources were replaced, L-asparagine was the nitrogen source (as per the control medium). Means followed by the same letter within a column are not significantly different at P < 0.01 according to the Duncan multiple range test.