Mutation of Aspergillus niger for hyperproduction of citric acid from black strap molasses

Spore suspensions of Aspergillus niger GCB 75, which produced 31.1 g/l citr ic acid from 15% sugars in molasses, were subjected to u.v.-induced mutagen esis. Among three variants, GCM 45 was found to be the best citric acid pro ducer and was further improved by chemical mutagenesis using NTG. Out of 3 deoxy-D-glucose-resistant variants, GCM 7 was selected as the best mutant w hich produced 86.1 +/- 1.5 g/l citric acid after 168 h of fermentation of p otassium ferricyanide + H2SO4-pretreated black strap molasses (containing 1 50 g sugars/l) in Vogel's medium. On the basis of comparison of kinetic par ameters, namely the volumetric substrate uptake rate (Q(s)), and specific s ubstrate uptake rate (q(s)), the volumetric productivity, theoretical yield and specific product formation rate, it was observed that the mutants were faster growing organisms and had the ability to overproduce citric acid.