Selection of a hyperproducing strain of Aspergillus niger for biosynthesis of citric acid on unusual carbon substrates.

Several tens of mutants were obtained by UV irradiation of a spore suspension of Aspergillus niger. Producers yielding large amounts of citric acid were selected on a modified Czapek agar containing methyl red as pH indicator. After a submerged cultivation in flasks with baffles, a mutant characterized by yellow pigmentation on wort agar and by yields of citric acid up to 74.6% in the medium containing glucose was chosen from 130 isolates tested.