CITRIC-ACID PRODUCTION FROM CELLOBIOSE BY 2-DEOXYGLUCOSE-RESISTANT MUTANT STRAINS OF ASPERGILLUS-NIGER IN SEMISOLID CULTURE

Citric acid production from cellobiose by Aspergillus niger was studie d by a semi-solid culture method using bagasse as a carrier. From the parental strain Yang no. 2, mutant strains showing resistance to 2-deo xy-D-glucose (DG) on minimal medium containing glucose as a carbon sou rce were induced. The representative mutant strain M155 was selected a nd subjected to further mutation. The new series of mutant strains sho wing resistance to DG on minimal medium containing cellobiose as a car bon source was induced, and among them the best mutant strain C192 sho wed higher citric acid productivity than Yang no. 2 in semisolid cultu re when glucose was used as a carbon source. Moreover, in semi-solid c ulture, the strain C192 produced 49.6 g/l of citric acid, 1.6 times as much citric acid as Yang no. 2 produced, from 100 g cellobiose/1 and showed enhanced beta-glucosidase production. In shake culture, the ext racellular beta-glucosidase activity of C192 was higher than that of Y ang no. 2 when not only cellobiose but also glucose and glycerol, cata bolite repressors, were used as a carbon source. These results indicat e that mutant strains such as C192 are insensitive to catabolite repre ssion.