CITRIC-ACID ACCUMULATION BY CYCLOHEXIMIDE SENSITIVE MUTANT STRAINS OFASPERGILLUS-NIGER

Mutants having impaired protein synthesis, that is cycloheximide-sensi tive mutants of a citric-acid-hyper-accumulating strain, were induced from Aspergillus niger. WU-2223L. Selection was on the basis of a pres umption that the mutants should be more sensitive to cycloheximide tha n WU-2223L. In shake culture without methanol as a promotor substance, seven mutants accumulated approximately 1.8-3.5 times as much citric acid as WU-2223L. The best mutant, CHM I-C3, accumulated 69.4 mg citri c acid/ml from 120 mg glucose/ml in shake culture without methanol, th is amount being 1.1 times the amount accumulated by WU-2223L with meth anol. Furthermore, under the conditions without methanol the mutants a ppeared to be more efficient than WU-2223L in employing the consumed g lucose for the accumulation of citric acid. It was also confirmed that CHM I-C3 exhibited a significantly increased level of intracellular N H4+ accumulation. The addition of 2% (v/v) methanol or 20 mu g cyclohe ximide/ml to the medium caused a remarkable increase of citric acid ac cumulation by WU-2223L: about 3.1 and 2.4 times respectively. However, the addition of these substances produced negative effects on citric acid accumulation by the mutants. With 2% (v/v) methanol, WU-2223L sho wed a remarkably decreased level of protein accumulation but a substan tially increased level of intracellular NH4+ accumulation. However, th ese phenomena were also observed in CHM I-C3 without methanol. These r esults indicate that the intracellular circumstances of the cyclohexim ide-sensitive mutants without methanol were similar to those of WU-222 3L with methanol, and that the impairment of protein synthesis contrib uted to increased citric acid accumulation by the mutants in the absen ce of methanol.