Gene expression of Aspergillus flavus strains on a cheese model system to control aflatoxin production

摘要

The expression of genes associated with aflatoxinbiosynthesis by different Aspergillus flavus strains growingon a cheese model system has not been studied.To control aflatoxin biosynthesis, it would be usefulto understand the changes in gene expression duringcheesemaking and relate those changes to toxin production.The objective of this study was to evaluate theeffects of pH, water activity, and temperature on theexpression of 2 regulatory genes (aflR and aflS) and 1structural gene (aflP) involved in aflatoxin biosynthesis,using 3 aflatoxigenic A. flavus strains growing ona cheese-based medium and reverse-transcription realtimePCR. The gene expression patterns were influencedby A. flavus strain and environmental conditions.The structural gene aflP and the regulatory genes aflRand aflS showed similar expression patterns in each A.flavus strain, but we also observed inter-strain differences.We observed the highest expression levels at 6and 9 d of incubation by A. flavus strains CQ8 andCQ103, and saw a decrease in the days following. StrainCQ7 showed the lowest expression of these genes. Weobserved the highest expression levels of these genesat pH 5.5, water activity 0.95, and 20 to 25°C; strainCQ103 showed a different pattern for the aflS gene,with maximum expression at pH 6.0 on d 6 of incubation.For the 3 strains, we found a strong correlationbetween the relative expression of the aflR and aflSgenes and the concentration of aflatoxins under conditionsthat simulated cheese ripening. Control strategiesto avoid aflatoxin contamination during cheesemakingcould use the detection of regulatory gene expression.