Direct production of citric acid from starch by a 2-deoxyglucose-resistant mutant strain of Aspergillus niger

Citric acid production from starch by Aspergillus niger was studied by the shake and semi-solid culture methods. For citric acid production, the parental strain Yang no. 2 and a 2-deoxyglucose (DG)-resistant mutant strain, C192, were used. When cultivated in shake culture with 140 g/l soluble starch as a carbon source, strain C192 produced 69.5 g/l of citric acid, 1.54 times that produced by Yang no. 2, and showed enhanced glucoamylase production (a maximum level of 0.134 mu kat/ml at 5 d). From a practical viewpoint, direct production of citric acid from corn- and potato starch was examined using the semi-solid culture method. When cultivated in a semi-solid culture using bagasse as a carrier, C192 produced 107.4 and 92.9 g/l of citric acid, approximately 1.14 and 1.09 times as much as Yang no. 2, from 200 g/l of corn- and potato starch, respectively. C192 exhibited enhanced glucoamylase production during the entire cultivation periods in comparison with that of Yang no. 2.