Oxidant/antioxidant balance inAspergillus parasiticus affects aflatoxin biosynthesis

Abstract

A close correlation between lipoperoxide formation in cells ofAspergillus parasiticus and aflatoxin biosynthesis has been established in rich and poor media in which oxidative stress was induced by addition of cumene hydroperoxide, a lipoperoxidation inducer. The presence of hydroperoxides of linoleic acid inA. parasiticus mycelia was analysed by liquid chromatography-mass spectrometry (LC-MS). This relation appears to be driven by activation of certain oxidative stress related transcription factors, such asyap1-like,skn7-like andhsf2-like. Activation of these factors then leads to the promotion of transcription of genes encoding antioxidant-related enzymes, such as superoxide dismutase, catalase and glutathione peroxidase.The incomplete seavenging of intracellular oxidation inA. parasiticus cells can lead to aflatoxin biosynthesis. The relationship between oxidative stress and aflatoxin biosynthesis is indicated by the high correlation among increased activity of lipoperoxidation and the antioxidant defence system with formation of aflatoxins.With regard to the relationship of oxidative stress and aflatoxin biosynthesis, the mechanism of action of butylated hydroxyl anisole (BHA), an antioxidant compound, in the control of aflatoxin biosynthesis was also investigated. Results indicate this compound can act,per se, by inhibiting lipoperoxidation and by inducing antioxidative defence responses of the fungal cell.

Modulation of Antioxidant Defense in Aspergillus parasiticus Is Involved in Aflatoxin Biosynthesis: a Role for the Ap yapA Gene

“…In yeast, Yap1 modulates the expression of many antioxidantrelated genes (2,16,45). The expression of the ApyapA gene (Yap1 orthologue) is correlated with responsiveness to oxidative stress (54). Mutants (n ϭ 20) with the ApyapA gene deleted were generated to assess whether ApYapA acts as a sensor of oxidative stress and a modulator of cell antioxidative responses also in A. parasiticus NRRL 2999.…”

“…Hydroperoxyoctadecadienoic acids (9-and 13-HPODE) present in the mycelia were analyzed following triple extraction with chloroform-methanol (2:1, vol/vol) in the presence of 100 g of butylated hydroxytoluene as antioxidant. Peroxides in the extracts were reduced with NaBH 4 to obtain hydroxyoctadecadienoic acids (9-and 13-HODE), as previously reported (54). Neither 9-HODE nor 13-HODE was detected in the extracts before reduction.…”

“…RNA was treated with RNase-free DNase I and then resuspended in 20 l of diethyl pyrocarbonate-treated water. RNA was extracted at different points in time (from 10 to 168 h; three tubes for each point in time) from A. parasiticus PDB culture and was used to develop an aflR, norA, ApyapA, Aphsf2, and Apskn7 RT-PCR assay, as previously reported (54). A semiquantitative analysis was conducted by performing RT-PCR amplification under several different conditions, in which the annealing temperature (from 55°C to 65°C), amplification cycles (from 20 to 35), and cDNA quantity (1 to 25 ng) were optimized to obtain a reproducible and reliable amplification curve capable of indicating the best conditions for revealing significant differences in the level of mRNA expression in comparing the various points in time and the different strains.…”

Apyap1affects aflatoxin biosynthesis duringAspergillus parasiticusgrowth in maize seeds

“…Hydroperoxyoctadecadienoic acids (HPODEs) present on the surface of maize seeds were analysed after extraction of the samples with chloroform:methanol 2:1 v/v (20 ml x 3) in presence of 100 µg of butylated hydroxytoluene (BHT) as an antioxidant. The two hydroxyoctadienoic acids (9-HODE and 13-HODE) obtained by reduction of the respective HPODEs, were analyzed by HPLC-APCI-MS as reported by Reverberi et al (2006). Data were collected and analyzed using the Chemstation LC/MSD revision A.09.01…”

Aflatoxins: biosynthesis, prevention and eradication

“…has been extensively studied, and has been shown to be connected to reactive oxygen species (ROS) formation and oxidative stress responses (Zaccaria et al, 2015). The AF biosynthesis is not only regulated by intracellular ROS of different origins (Reverberi et al, 2006;Grintzalis et al, 2014), but the AF biosynthetic pathway itself may serve as a source of ROS due to involvement of P450 enzymes (Roze et al, Tab. 1.…”