Figure 2. Effect of different nitrogen sources on β-xylosidase production by K. marxianus PPY125 (light squares) and its mutant M125 (dark squares). Organisms were grown on xylose (20 g/l, w/v) containing different nitrogen sources (1 = ammonium nitrate; 2 = ammonium sulphate; 3 = corn steep liquor; 4 = soybean meal; 5 = sodium glutamate; 6 = sodium nitrate; 7 = urea; and 8 = peptone) at a rate of 1.1 g/l equivalent to that contained in ammonium sulphate in triplicate. Flasks were harvested and processed as described in Materials and Methods. Each value is a mean of three independent experiments.Error bars represent standard deviation among three replicates.