Aflatoxin genes and the aflatoxigenic potential of Koji moulds

Area of Science:

• Food Microbiology
• Mycology
• Molecular Biology

Background:

• Aspergillus species are widely used in food fermentation.
• Some Aspergillus species, like A. flavus, can produce harmful aflatoxins.
• Understanding the genetic basis of aflatoxin production is crucial for food safety.

Purpose of the Study:

• To identify and characterize aflatoxin gene presence and deletions in Aspergillus isolates from food fermentations.
• To correlate genetic variations with aflatoxin production capabilities.

Main Methods:

• Screening of 64 Aspergillus isolates and 18 reference strains for aflatoxin genes (aflR, omt-1, pksA, nor-1).
• Utilizing hybridization patterns and restriction fragment length polymorphisms (RFLPs) to detect gene deletions and variations.
• Assessing aflatoxin B1 production in selected strains under inducing conditions.

Main Results:

• Significant percentages of A. oryzae (27%) and A. flavus (93%) strains lacked key aflatoxin genes (aflR, omt-1).
• Large deletions within the aflatoxin gene cluster were observed in some strains, with a suggested deletion polarity.
• Strains with deleted or polymorphic aflatoxin genes were unable to produce aflatoxins or produced only trace amounts.
• Even without apparent deletions, 73% of A. oryzae strains did not produce detectable aflatoxin B1.

Conclusions:

• Genetic variations, including deletions and polymorphisms in aflatoxin gene clusters, are common in food-derived Aspergillus strains.
• These genetic defects directly correlate with the inability to produce aflatoxins.
• Many A. oryzae strains, even those without detectable deletions, are non-producers of aflatoxin B1, suggesting other regulatory mechanisms at play.