Inhibition of aflatoxin metabolism and growth ofAspergillus flavusin liquid culture by a DNA methylation inhibitor

Abstract

Aflatoxins (AFs) are a group of highly oxygenated polyketidese-derived toxins mainly produced by Aspergillus flavus and A. parasiticus, whose biosynthesis mechanisms are extremely sophisticated. Methylation is known as the major form of epigenetic regulation, which is correlated with gene expression. As the DNA methylation inhibitor 5-azacytidine (5-AC) blocks AF production, we studied AFB1 metabolism and morphological changes of A. flavus by treatment with 5-AC in liquid culture. The results show that 5-AC caused a decrease in AF production and concurrent changes in morphology. In addition, we isolated a non-aflatoxigenic mutant of A. flavus, showing a significant reduction in pigment production, after 5-AC treatment. This mutant showed significant reduction in the expression of genes in the AF biosynthesis pathway, and conidia formation. Furthermore, as AF biosynthesis and oxidative stress are intimately related events, we assessed the viability of A. flavus to oxidative stress after treatment with 5-AC, which showed that the mutant was more sensitive to the strong oxidant hydrogen peroxide. We found that the non-aflatoxigenic mutant showed a decrease in reactive oxygen species (ROS) and metabolites indicative of oxidative stress, which may be caused by the disruption of the defence system against excessive ROS formation after 5-AC treatment. These data indicate that 5-AC, as an inactivator of DNA methyltransferase, plays a very important role in AFB1 metabolism and the development of A. flavus, which might provide an effective strategy to pre- or post-harvest control of AFs.

Adenylate Cyclase AcyA Regulates Development, Aflatoxin Biosynthesis and Fungal Virulence in Aspergillus flavus

“…Aspergillus flavus is a saprophytic soilborne fungus that contaminates food-stuffs and a broad range of important agricultural crops, including maize, peanut, and cottonseed, with the most carcinogenic metabolite, aflatoxins (AFs) (Amaike and Keller, 2011; Yang et al, 2015). This fungus is also one of the most opportunistic pathogen of human and animals causing aspergillosis diseases or liver cancer either through consumption of contaminated food or through invasive growth (Hedayati et al, 2007; Amaike and Keller, 2011; Yang et al, 2015).…”

“…This fungus is also one of the most opportunistic pathogen of human and animals causing aspergillosis diseases or liver cancer either through consumption of contaminated food or through invasive growth (Hedayati et al, 2007; Amaike and Keller, 2011; Yang et al, 2015). Because of this, A. flavus causes food shortages, significant economic losses and health problems all over the world especially in warm and moist fields (Amaike and Keller, 2011; Bai et al, 2015).…”

Functional Analysis of the Nitrogen Metabolite Repression Regulator Gene nmrA in Aspergillus flavus

“…Aflatoxins (AFs), mainly produced by A. flavus and A. parasiticus , have been identified as a class of the most toxic and carcinogenic secondary metabolites of fungi. AF contamination of agricultural grains is not only a significant food safety concern but also an economic concern for the agricultural industry worldwide (Yu, 2012; Amaike et al, 2013; Yang et al, 2015). To develop effective and novel strategies against AF contamination, it is a necessity to investigate the molecular mechanisms by which AF biosynthesis is regulated in A. flavus .…”

Aflatoxins: biosynthesis, prevention and eradication

“…AF biosynthesis is extremely sophisticated (Klich, 2007;Yang et al, 2015). Generally, the AF biosynthesis genes of the most known AF producers, A. flavus and A. parasiticus, are highly homologous and the order of 25 genes within the AF gene clusters in the two organisms has been shown to be identical (Jiujiang et al, 1995).…”

“…The mechanism of AF biosynthesis has been extensively studied, and recent investigations have shown that about 30 clustered genes and more than 23 steps of enzymatic reactions are involved in the AF biosynthetic pathway (Georgianna and Payne, 2009;Yu, 2012;Yang et al, 2015). AF biosynthesis is extremely sophisticated (Klich, 2007;Yang et al, 2015).…”