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Aflatoxin genes and the aflatoxigenic potential of Koji moulds
P van den Broek1, A Pittet, H Hajjaj
1Nestlé Research Centre, Lausanne, Switzerland. peter.van-den-broek@rdls.nestle.com
Abstract:
Sixty-four Aspergillus isolates, 54 of which originated from food fermentations, and 18 Aspergillus reference strains were identified and screened for the presence of aflatoxin genes aflR and omt-1. Among the Koji moulds, not only A. oryzae but also A. flavus strains were found. Furthermore, 27% of A. oryzae and 93% of A. flavus strains lacked either aflR or both aflR- and omt-1. A selection of 29 strains was also checked for the presence of pksA and nor-1. This revealed large deletions in the aflatoxin gene cluster of some strains. The hybridisation patterns also suggested a polarity in the deletion events, originating in the vicinity of pksA and extending towards omt-1. Other strains exhibited BamHI restriction fragment length polymorphisms (RFLPs) for either aflR or for aflR and omt-1. All aflR and/or omt-1 deletion strains turned out to be unable to produce aflatoxin. The RFLP-carrying strains either produced only traces of aflatoxin or none at all. In 73% of the A. oryzae strains, no apparent deletions were detected with the aflR and omt-1 probes. Nevertheless, after incubation in aflatoxin-inducing media, no aflatoxin B1 production could be detected in those A. oryzae strains.
Insights
Many Aspergillus strains, including those used in food, lack aflatoxin genes, preventing toxin production. This study investigates genetic variations in Aspergillus species, crucial for food safety and fermentation processes.
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.