Absence of aflatoxin biosynthesis in koji mold (Aspergillus sojae)

Ten strains isolated from industrial soy sauce producing koji mold were ide ntified as Aspergillus sojae and distinguished from Aspergillus parasiticus morphologically and physiologically. There was no detectable aflatoxin in any culture extracts of A. sojae strains. Strain 477 was chosen as a repres entative strain of industrial A. sojae for further molecular analysis. All enzymatic activities associated with the aflatoxin biosynthesis were not de tected or negligible in strain 477 compared with that of the A. parasiticus strain. Southern analysis suggested that the genomic DNA of strain 477 con tained aflatoxin biosynthetic pathway genes. In contrast, all industrial st rains lacked detectable transcripts of aflR, the main regulatory gene for a flatoxin biosynthesis, under the aflatoxin-inducing condition. Our data sug gest that defects in aflR expression cause the lack of expression of aflato xin-related genes which results in the absence of aflatoxin biosynthesis in A. sojae strains.