Citric acid production from cellulose hydrolysate by a 2-deoxyglucose- resistant mutant strain of Aspergillus niger

Citric acid production from cellulose hydrolysate was done by a semi- solid culture of Aspergillus niger Yang no. 2, a parental strain, and C192, which is a 2-deoxy-D-glucose-resistant mutant strain. Cellulose powder was hydrolyzed to mainly glucose and a low concentration of cellobiose by a commercial cellulase in acetate or citrate buffer. The hydrolysate prepared in acetate buffer was concentrated to contain 150 g/l of reducing sugars and used as a medium for fermentation. Yang no. 2 and C192 produced 77.9 g/l and 98.7 g/l of citric acid in 9 days from the concentrated hydrolysate, respectively. Acetate buffer delayed the fermentation. When the hydrolysate was prepared in citrate buffer and used as a medium, Yang no. 2 and C192 produced 92.2 g/l and 102.3 g/l of citric acid within 3 days from the concentrated hydrolysate containing 150 g/l of reducing sugars, respectively. It is concluded that citric acid production from cellulose hydrolysate with high conversion yield, maximally 68.2% based on the reducing sugars supplied, was achieved first by C192.