Supplementation of nitrogen sources. 1 yeast extract, 2 peptone, 3 urea, 4 corn steep solids, 5 (NH4)2HPO4, 6 KNO3, 7 NH4HCO3, 8 NH4Cl, 9 (NH4)2SO4, 10 control (without nitrogen supplement). The culture conditions were particle size of wheat bran: 500-1000 μm; moisture: 70%; pH of the mineral salt solution: 6.0; inoculum size 5 mL and temperature 30°C with 1% pectin as carbon supplement. The mineral salt solution used for the experiment was devoid of (NH4)2SO4.