Breeding of starch-utilizing and itaconic-acid-producing koji molds by interspecific protoplast fusion between Aspergillus terreus and Aspergillus usamii

Interspecific protoplast fusion between Aspergillus terreus, an itaconic acid producer, and A. usamii, a glucoamylase producer, was done to breed new koji molds producing itaconic acid from starch. Protoplast fusion between auxotrophic mutant strains by poly(ethylene glycol) treatment produced prototrophic fusants with a fusion frequency of 10^-5-10^-4. The stabilities of some fusants obtained were confirmed by successive subcultures. Conidial analyses of DNA contents and the number of nuclei indicated that the fusants obtained were haploids like the parental strains. One of the stable fusants, F-112, morphologically resembled A. terreus, and produced maximally 35.9 mg/ml itaconic acid from soluble starch (120 mg/ml) at day 6 of cultivation. This productivity from soluble starch was five times as high as that of A. terreus and 70% of that of A. terreus from glucose (120 mg/ml).