Genetic diversity of aflatoxin-producing Aspergillus flavus isolated from selected groundnut growing agro-ecological zones of Uganda

Aspergillus population diversity and its role in aflatoxin contamination of cashew nuts from coastal Kenya

Cashew nuts are among the main cash crops in coastal Kenya, due in large part to their high nutritional value. Unfortunately, they also make them highly susceptible to mold contamination, resulting in biodeterioration of the nutritional value and potential contamination with toxic secondary metabolites, such as aflatoxins, that cause them to be rejected for sale at the market. We determined the population diversity of the Aspergillus species and their role in aflatoxin contamination in cashew nuts in selected coastal regions of Kenya. Fifty raw cashew nut samples were collected from post-harvest storage facilities across three counties in Kenya's coastal region and examined for moisture content and the presence of Aspergillus fungi. About 63 presumptive isolates were recovered from the cashew nuts. ITS and 28S rDNA regions were sequenced. The aflD, aflM and aflR genes were amplified to identify the potentially aflatoxigenic from the Aspergillus isolates. The Aflatoxins' presence on the isolates was screened using UV and the ammonia vapour test on coconut milk agar and validated using ELISA assay. A comparison of cashew moisture content between the three counties sampled revealed a significant difference. Sixty-three isolates were recovered and identified to section based on morphological characters and their respective ITS regions were used to obtain species identifications. Three sections from the genus were represented, Flavi and Nigri, and Terrei with isolates from the section Nigri having slightly greater abundance (n = 35). The aflD, aflM and aflR genes were amplified for all isolates to assess the presence of the aflatoxin biosynthesis pathway, indicating the potential for aflatoxin production. Less than half of the Aspergillus isolates (39.68%) contained the aflatoxin pathway genes, while 22.22% isolates were aflatoxigenic, which included only the section Flavi isolates. Section Flavi isolates identification was confirmed by calmodulin gene. The presence of species from Aspergillus section Flavi and section Nigri indicate the potential for aflatoxin or ochratoxin in the cashew nuts. The study established a foundation for future investigations of the fungi and mycotoxins contaminating cashew nuts in Kenya, which necessitates developing strategies to prevent infection by mycotoxigenic fungi, especially during the storage and processing phases.

The epigenetic regulator Set9 harmonizes fungal development, secondary metabolism, and colonization capacity of Aspergillus flavus

As a widely distributed food-borne pathogenic fungus, Aspergillus flavus and its secondary metabolites, mainly aflatoxin B1 (AFB1), pose a great danger to humans. It is urgent to reveal the complex regulatory network of toxigenic and virulence of this fungus. The bio-function of Set9, a SET-domain-containing histone methyltransferase, is still unknown in A. flavus. By genetic engineering means, this study revealed that, through catalyzing H4K20me2 and -me3, Set9 is involved in fungal growth, reproduction, and mycotoxin production via the orthodox regulation pathway, and regulates fungal colonization on crop kernels through adjusting fungal sensitivity reactions to oxidation stress and cell wall integrity stress. Further domain deletion and point mutation inferred that the SET domain is the core element in catalyzing H4K20 methylation, and D200 site of the domain is the key amino acid in the active center of the methyltransferase. Combined with RNA-seq analysis, this study revealed that Set9 regulates the aflatoxin gene cluster by the AflR-like protein (ALP), other than traditional AflR. This study revealed the epigenetic regulation mechanism of fungal morphogenesis, secondary metabolism, and pathogenicity of A. flavus mediated by the H4K20-methyltransferase Set9, which might provide a potential new target for early prevention of contamination of A. flavus and its deadly mycotoxins.

Distribution, Genetic Diversity and Biocontrol of Aflatoxigenic Aspergillus flavus in Serbian Maize Fields

Maize is one of the leading export products in the Republic of Serbia. As a country where economic development depends on agriculture, maize production plays a critical role as a crop of strategic importance. Potential aflatoxin contamination of maize poses a risk to food and feed safety and tremendous economic losses. No aflatoxin contamination of maize samples harvested in 2019 and 2020 in different localities in the Republic of Serbia was detected by the Enzyme-Linked Immunosorbent Assay (ELISA) test and High-Performance Liquid Chromatography (HPLC) method. On the other hand, the Cluster Amplification Patterns (CAP) analyses of the isolated Aspergillus flavus strains from 2019 maize samples confirmed the presence of key biosynthesis genes responsible for aflatoxin production. Artificial inoculation and subsequent HPLC analysis of the inoculated maize samples confirmed the high capacity of the A. flavus strains for aflatoxin production, pointing to a high risk of contamination under favorable conditions. Prevention of aflatoxin contamination is primarily based on A. flavus control, where biocontrol agents play a significant role as sustainable disease management tools. In this study, antagonistic activity screening of the novel strains belonging to the Bacillus genus indicated superior suppression of A. flavus strains by two Bacillus strains isolated from the rhizosphere of Phaseolus vulgaris.

Aspergillus Section Flavi from Four Agricultural Products and Association of Mycotoxin and Sclerotia Production with Isolation Source

Many agricultural products are susceptible to contamination by aflatoxin-producing species from Aspergillus section Flavi. The objectives of this study were to determine the occurrence of Aspergillus section Flavi in four agricultural products, such as pistachio, walnut, hazelnut, and dried fruits, collected from market and retail shops in various areas of Kerman County and obtain information on the relationships between isolation source and ability to produce sclerotia and potential for aflatoxin production. Aspergillus species were identified based on morphological characteristics as well as subsequent sequencing of the parts of the β-tubulin and calmodulin genes. From 207 isolated strains, the following species were identified: A. flavus, A. tamarii A. nomius, A. parasiticus, A. arachidicola, A. caelatus, A. pseudotamarii, and A. leporis. To the best of our knowledge, this is the first report of A. pseudotamarii and A. arachidicola with the potential to produce aflatoxins from dried apricots and hazelnuts, respectively. Sclerotial type was significantly different between isolates from different isolation sources. From 192 tested isolates, 38% were aflatoxin producer from which 5% were scored as strong aflatoxin producers and 33% as average aflatoxin producers. A significant difference in the population of aflatoxin-producing strains across the isolation sources was observed which may reflect host adaptation and thereby different vulnerabilities to aflatoxin-producing species among the examined products.