Submitted to: Multicrop Aflatoxin and Fumonisin Elimination and Fungal Genomics Workshop-The Peanut Foundation
Publication Type: Proceedings
Publication Acceptance Date: 10/18/2007
Publication Date: 10/21/2007
Citation: Accinelli, C., Abbas, H.K., Zablotowicz, R.M., Wilkinson, J.R. 2007. Aspergillus Flavus/Aflatoxin Occurrence and Expression of Aflatoxin Biosynthesis Genes in Soil. Multicrop Aflatoxin and Fumonisin Elimination and Fungal Genomics Workshop-The Peanut Foundation. p.68 Interpretive Summary:
Technical Abstract: Aflatoxins (AF) are carcinogenic metabolites produced by several species of Aspergillus, including A. flavus. Although A. flavus is readily isolated from environmental samples, soil and plant material are considered the natural habitat of this fungus. Studies were conducted on a Dundee silt loam to ascertain the ecology of A. flavus in soil planted in corn the previous year and to estimate the occurance and fate of AFB1 in soil. This soil was previously planted in Bt or non Bt corn and soil was sampled from five plots of each corn hybrid. Low levels of AF B1 (0.4 to 5.5 ng g-1) were detected in soil, but recovery was variable among replicate samples. Native soil and autoclaved soil was amended with 10.0 ng g-1 AFB1 and incubated at 25oC. These soils were extracted with ethyl acetate at 0, 3, 6, 13, and 17 days after treatment and analyzed by HPLC. A rapid loss of extractable AF occurred in non-sterile soil (half life ' 5 days) which was not observed in autoclaved soil indicating biological detoxification. Plate counts using semi-selective media (MDRB agar) indicated this soil contained log (10) 3.1 to 4.5 propagules of A. flavus g-1 soil. Based on cultural methods, about 66% of these A. flavus were capable of AF synthesis. Using traditional PCR all five genes were detected in all soils cofirming the plate count estimates of an abundant native A. flavus population. Reverse transcriptase (RT-PCR) analysis showed that the two regulatory genes, aflR and aflS, and structural genes, including afllD, aflG and aflP, of the AF biosynthesis pathway were expressed in surface soil. These data suggests that indigenous soil populations of A. flavus are physiologically active and have the potential to express several genes involved in AF biosynthesis in surface 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.