Taxonomy of Yellow koji mold (Aspergillus flavus/oryzae) in Korea

Koji molds are comprised of yellow, black and white. Black and white koji molds were recently re-visited by this author and it is concluded that they consists of Aspergillus luchuesnsis, A. niger and A. tubingensis, and the most important species for alcoholic beverage production is A. luchuensis. In the case of yellow koji mold, it is comprised of Aspergillus oryzae, A. sojae and A. tamari. In the case of A. sojae, the species is scarcely isolated from nature and rarely used for industry in Korea. Aspergillus tamari is often isolated from traditional Korean Meju, a fermented soybean product, and the classification of the species is clear. However, in the case of A. oryzae, differentiation between A. oryzae and A. flavus is still in controversy. In this study, we collected 415 strains of Aspergillus flavus/oryzae complex from air, rice straw, soybean, corn, peanut, arable soil and Meju in Korea and we examined the aflatoxin producing capacity of the strains. The norB-cypA, omtA and aflR genes in the aflatoxin biosynthesis gene cluster were analyzed. We found that 367 strains (88.4%) belonged to non-aflatoxigenic group (Type I of norB-cypA, IB-L-B-, IC-AO, or IA-L-B- of omtA, and AO type of aflR), and only 48 strains (11.6%) belonged to aflatoxin-producible group (Type II of norB-cypA, IC-L-B+/B- or IC-L-B+ of omtA, and AF type of aflR). In the case of A. flavus/oryzae strains from Meju, almost strains (178/192, 92.7%) belonged to non-aflatoxigenic group and only 14 strains (7.3 %) belonged to aflatoxin-producible group. It is proposed in this study that non-aflatoxigenic strain from Meju is classified as A. oryzae, considering that Meju is food material.