Influence of sub-lethal doses, water potential and temperature on growth sclerotia, aflatoxins and aflD(=nor-1) expression by Aspergillus flavus RCPO8108

Abstract

Effects of interacting conditions of sub-lethal levels of antioxidants, water potential (Ψ) and temperature were evaluated on growth, sclerotial characteristics, aflatoxin B 1 (AFB 1) production and aflD (=nor-1) gene expression by Aspergillus flavus strain RCP08108. These studies were carried out on peanut meal extract agar osmotically modified to -2.8,-7.1, -9.9 and -16.0MPa and incubated at 28 and 20°C. The food grade antioxidants added were butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT) at (1+1mM-M1) and (5+5mM-M2). To relate the aflD expression after toxigenic A. flavus grew under interacting stress conditions, real-time PCR was used. Antioxidant mixtures caused a higher and significant (p<0.001) reduction in growth rate. The major impact on size and volume sclerotia was produced by Ψ; followed by antioxidant mixtures. High AFB 1 levels were observed in response to the M1 applied at -7.1MPa. Induction of the aflD gene was observed in response to the M1 treatment at -2.8, -7.1 and -9.9MPa; but significant decreases of AFB 1 production and aflD transcripts were observed; when the fungus grew in the presence of the M2 treatment.These results showed that it is necessary to apply food-grade antioxidants into the peanut storage system at levels higher than 5mM. This is an important tool to avoid sub-lethal antioxidant doses that can lead to fungal growth, increase resistance structures, and stimulate aflD gene expression and AFB 1 accumulation in this substrate.