Submitted to: Canadian Journal of Microbiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/24/2008
Publication Date: 4/22/2008
Citation: Accinelli, C., Abbas, H.K., Zablotowicz, R.M., Wilkinson, J.P. 2008. Aspergillus flavus Aflatoxin Occurrence and Expression of Aflatoxin Biosynthesis Genes in Soil. Canadian Journal of Microbiology. (54:371-379) Interpretive Summary: Soil and plant residues are major reservoirs for sustaining the mold, Aspergillus , that is responsible for contamination of corn with toxins (aflatoxins). Thus, understanding the ecology of Aspergillus is required to effectively manage aflatoxin contamination of corn. Cooperative studies between a scientist from the University of Bologna (Italy), Mississippi State University and ARS scientists evaluated several factors relating to the occurrence of aflatoxin in soil and used genetic techniques to study the activity of aflatoxin production in soil. Aflatoxin was found in all soil studied but it’s concentration was higher in decaying corn vegetation on the soil surface. All soils possessed DNA for five genes that encode for aflatoxin production, and by using a technique called RT-PCR it was determined these five genes are actually expressed in soil. The relationship between soil Aspergillus populations and molecular detection techniques may be useful in predicting the contribution of soil microflora to mycotoxin contamination.
Technical Abstract: The carcinogen, aflatoxin B1 (AFB1) produced by Aspergillus flavus, is a major food safety concern in crops. However, information on AFB1 occurrence in soil and crop residue is scarce. A series of experiments investigated the occurrence of AFB1 in soil and corn residues, and ascertained the ecology of A. flavus in a Dundee silt loam soil. Samples of untilled soil (0 to 2 cm) and residues were collected in March 2007 from plots previously planted with a corn isolines containing the Bacillus thurengiensis endotoxin gene (BT) or non-Bt isolines. Aflatoxin B1 levels were significantly different in various corn residues. The highest AFB1 levels were observed in cobs containing grain, with 145 and 275 ng g-1, in Bt and non-Bt, respectively (Pr ' F = 0.001). Aflatoxin levels averaged 3.3 and 9.6 ng g-1 in leaves/stalks and cobs without grain, respectively. All soils had AFB1 ranging from 0.9 to 5.5 ng g-1 with similar levels in plots from Bt and non-Bt corn. Based on cultural methods, soil contained from log (10) 3.1 to 4.5 A. flavus CFU g-1 with about 60% of isolates producing aflatoxin. Laboratory experiments demonstrated that AFB1 is rapidly degraded in soil at 28oC (half-life ' 5 days). The potential of the soil A. flavus to produce aflatoxins was confirmed by molecular methods. Transcription of five aflatoxin biosynthesis genes including afllD, aflG, aflP, aflR and aflS were detected by RT-PCR analysis in soil. Although AFB1 appears to be transient in soils, it is clear that AFB1 is produced in surface soil in the presence of corn residues as indicated by A. flavus CFU levels, AFB1 detection, and expression of aflatoxin biosynthetic genes.