Absence of aflatoxin biosynthesis in koji mold ( Aspergillus sojae )

Abstract

Ten strains isolated from industrial soy sauce producing koji mold were identified 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 representative strain of industrial A. sojae for further molecular analysis. All enzymatic activities associated with the aflatoxin biosynthesis were not detected or negligible in strain 477 compared with that of the A. parasiticus strain. Southern analysis suggested that the genomic DNA of strain 477 contained aflatoxin biosynthetic pathway genes. In contrast, all industrial strains lacked detectable transcripts of aflR, the main regulatory gene for aflatoxin biosynthesis, under the aflatoxin-inducing condition. Our data suggest that defects in aflR expression cause the lack of expression of aflatoxin-related genes which results in the absence of aflatoxin biosynthesis in A. sojae strains.

Nonfunctionality of Aspergillus sojae aflR in a Strain of Aspergillus parasiticus with a Disrupted aflR Gene

“…aflR homologues are found in non-aflatoxin-producing A. sojae, which is used industrially in food fermentation, but transcription of these homolgues is not detectable (20,27). Determining the cause of transcriptional loss of aflR in A. sojae is important because this fungus is used to produce products that are routinely used for human consumption.…”

“…These genes apparently are not transcribed (16,20,27). The molecular mechanisms that prevent production of aflatoxins by A. oryzae isolates have been examined only recently.…”

Anti-aflatoxigenic Effect of Some Lactobacillus Species on Aspergillus flavus by Using Real – Time - q PCR

“…In addition, other genes not belonging to the aflatoxin gene cluster might directly or indirectly control toxin production, as reported for VeA and LexA in A. nidulans and A. parasiticus (Cary et al, 2006). However, Watson et al (1999) and Matsushima et al (2001) revealed that the lack of a functional AflRs was insufficient to explain the complete repression of aflRs and other aflatoxin related genes in A. sojae.…”

Evaluation of the Aflatoxin Biosynthetic Genes for Identification of the Aspergillus Section Flavi

“…In nonaflatoxin-producing species, some mutation is observed within the gene cluster responsible for not only regulation of the expression but also the structural gene, resulting in the prevention of aflatoxin biosynthesis (11,20). In spite of the presence of aflatoxin biosynthetic genes, they never produce aflatoxins and have been used safely for food production.…”

“…sojae is generally recognized as an non-aflatoxinproducing strain (11) and is recognized as a safe koji mold for food fermentation processes, as is A. oryzae (2). Phylogenetic analyses based on the 18S rRNA gene and ITS region sequences cannot clearly distinguish strains of A. sojae from those of A. parasiticus and A. toxicarius (14); however, MLSA based on four aflatoxin biosynthetic genes showed that members of A. sojae were obviously distant from those of aflatoxin-producing strains, A. parasiticus and A. toxicarius (Fig.…”