Aspergillus flavus, Aflatoxins, and Their Effects on Crop Production and Food Safety

A special issue of Journal of Fungi (ISSN 2309-608X). This special issue belongs to the section "Environmental and Ecological Interactions of Fungi".

Deadline for manuscript submissions: closed (31 December 2021) | Viewed by 17065

Special Issue Editors


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Guest Editor
Department of Plant Pathology and Crop Physiology, Louisiana State University Agricultural Center, Baton Rouge, LA, USA
Interests: understanding host–fungus interactions between maize (corn) and Aspergillus flavus, the fungus that produces aflatoxins during the infection of susceptible crops; between soybean and Phakopsora pachyrhizi, the causal agent of soybean rust; and between soybean and Cercospora cf. flagellaris/ C. kikuchii, the pathogens causing Cercospora leaf blight; developing strategies to enhance host resistance in maize and soybean to these fungal diseases, such as the overexpression of host-resistance-associated genes or the suppression of key fungal genes through host-induced gene silencing (HIGS)

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Guest Editor
International Crops Research Institute for the Semi-Arid Tropics, Hyderabad, India
Interests: My major areas of interests include developing tools towards candidate gene discovery and validations, genetic and genome engineering for trait enhancement in grain legumes and dry land cereals. My lab works on generating fundamental knowledge about genetic mechanisms regulating the production of aflatoxins in groundnut and their role in fungal development and virulence. By gaining critical insights into complex regulation of host plant defense responses to aflatoxigenic fungi, the most efficacious gene products for aflatoxin control have been designed using transgenic as well as RNAi/ HIGS based interventions, and more recently by integrating cutting edge CRISPR-Cas based gene editing technologies.

Special Issue Information

Dear Colleagues,

Aspergillus flavus is a soil-borne opportunistic fungal pathogen that infects important agricultural crops such as maize, peanut, and cotton, and produces the most carcinogenic naturally occurring mycotoxin known as aflatoxin, which causes hundreds of millions of dollars in economic losses and serious illnesses in human and domestic animals due to the congestion of aflatoxin-contaminated food or feed, especially in developing countries. Therefore, A. flavus infection and the subsequent aflatoxin accumulation is a major economic and food safety concern worldwide, and the situation is expected to worsen as a result of global warming and the associated climate change. The aim of the current Special Issue is to share/present some of the most recent research efforts in detecting and reducing A. flavus infection in susceptible crops, such as breeding for aflatoxin-tolerant varieties, applying biocontrol agents, adopting effective cultural practices and various post-harvest measures, and to highlight the latest understanding on the regulation of aflatoxin biosynthetic pathway genes in the fungus, the metabolism of aflatoxins in human and domestic animals, and various approaches to detoxify aflatoxins through post-harvest processing to reduce its economic and health impacts.

Dr. Zhi-Yuan Chen
Dr. Pooja Bhatnagar-Mathur
Guest Editors

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Keywords

  • Aspergillus flavus;
  • aflatoxin contamination;
  • detection;
  • aflatoxin biosynthesis and regulation;
  • aflatoxin managment;
  • health and economic impacts

Published Papers (5 papers)

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Research

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18 pages, 5677 KiB  
Article
Aflatoxin Reduction and Retardation of Aflatoxin Production by Microorganisms in Doenjang during a One-Year Fermentation
by Vishal Kumar, Ashutosh Bahuguna, Srinivasan Ramalingam, Jong Suk Lee, Sung Soo Han, Hyang Sook Chun and Myunghee Kim
J. Fungi 2022, 8(2), 190; https://doi.org/10.3390/jof8020190 - 15 Feb 2022
Cited by 8 | Viewed by 2655
Abstract
Meju, a raw material for doenjang preparation, is highly vulnerable to aflatoxin-producing fungi. The aim of this study was to evaluate the effect of a one-year fermentation on aflatoxins and aflatoxin-producing fungi in doenjang spiked with aflatoxins B1, G1, B2, and G2 and [...] Read more.
Meju, a raw material for doenjang preparation, is highly vulnerable to aflatoxin-producing fungi. The aim of this study was to evaluate the effect of a one-year fermentation on aflatoxins and aflatoxin-producing fungi in doenjang spiked with aflatoxins B1, G1, B2, and G2 and inoculated with toxigenic Aspergillus flavus. A significant reduction in aflatoxins was observed after a year of fermentation, measuring 92.58%, 100%, 98.69%, and 100% of B1, G1, B2, and G2, respectively. After a year of fermentation, 6.95 ± 3.64 µg/kg of total aflatoxin was detected, which represents a 97.88% reduction in the total aflatoxin compared with the initial value (328.83 ± 36.60 µg/kg). Several aflatoxin-degrading fungi (Aspergillus versicolor, Cladosporium subcinereum, Aspergillus ochraceus) and bacteria (Bacillus albus, Bacillus velezensis) isolated from doenjang were identified as the major contributors to the reduction of aflatoxin. Furthermore, it was observed that most of the aflatoxin contamination in doenjang occurred during the meju stage, and this stage was found to be most susceptible to A. flavus contamination and growth. These findings reveal that native microorganisms mediate aflatoxin clean-up in doenjang during fermentation and support the use of such microorganisms as a starter culture for the preparation of aflatoxin-free doenjang. Full article
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21 pages, 4739 KiB  
Article
Peanut Seed Coat Acts as a Physical and Biochemical Barrier against Aspergillus flavus Infection
by Leslie Commey, Theophilus K. Tengey, Christopher J. Cobos, Lavanya Dampanaboina, Kamalpreet K. Dhillon, Manish K. Pandey, Hari Kishan Sudini, Hamidou Falalou, Rajeev K. Varshney, Mark D. Burow and Venugopal Mendu
J. Fungi 2021, 7(12), 1000; https://doi.org/10.3390/jof7121000 - 23 Nov 2021
Cited by 10 | Viewed by 3255
Abstract
Aflatoxin contamination is a global menace that adversely affects food crops and human health. Peanut seed coat is the outer layer protecting the cotyledon both at pre- and post-harvest stages from biotic and abiotic stresses. The aim of the present study is to [...] Read more.
Aflatoxin contamination is a global menace that adversely affects food crops and human health. Peanut seed coat is the outer layer protecting the cotyledon both at pre- and post-harvest stages from biotic and abiotic stresses. The aim of the present study is to investigate the role of seed coat against A. flavus infection. In-vitro seed colonization (IVSC) with and without seed coat showed that the seed coat acts as a physical barrier, and the developmental series of peanut seed coat showed the formation of a robust multilayered protective seed coat. Radial growth bioassay revealed that both insoluble and soluble seed coat extracts from 55-437 line (resistant) showed higher A. flavus inhibition compared to TMV-2 line (susceptible). Further analysis of seed coat biochemicals showed that hydroxycinnamic and hydroxybenzoic acid derivatives are the predominant phenolic compounds, and addition of these compounds to the media inhibited A. flavus growth. Gene expression analysis showed that genes involved in lignin monomer, proanthocyanidin, and flavonoid biosynthesis are highly abundant in 55-437 compared to TMV-2 seed coats. Overall, the present study showed that the seed coat acts as a physical and biochemical barrier against A. flavus infection and its potential use in mitigating the aflatoxin contamination. Full article
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21 pages, 2038 KiB  
Article
Resistance to Aflatoxin Accumulation in Maize Mediated by Host-Induced Silencing of the Aspergillus flavus Alkaline Protease (alk) Gene
by Olanike Omolehin, Yenjit Raruang, Dongfang Hu, Zhu-Qiang Han, Qijian Wei, Kan Wang, Kanniah Rajasekaran, Jeffrey W. Cary and Zhi-Yuan Chen
J. Fungi 2021, 7(11), 904; https://doi.org/10.3390/jof7110904 - 26 Oct 2021
Cited by 12 | Viewed by 2003
Abstract
Aspergillus flavus is a fungal pathogen that infects maize and produces aflatoxins. Host-Induced Gene Silencing (HIGS) has been shown to reduce host infection by various fungal pathogens. Here, the A. flavus alkaline protease (alk) gene was targeted for silencing through HIGS. [...] Read more.
Aspergillus flavus is a fungal pathogen that infects maize and produces aflatoxins. Host-Induced Gene Silencing (HIGS) has been shown to reduce host infection by various fungal pathogens. Here, the A. flavus alkaline protease (alk) gene was targeted for silencing through HIGS. An RNAi vector carrying a portion of the alk gene was incorporated into the B104 maize genome. Four out of eight transformation events containing the alk gene, Alk-3, Alk-4, Alk-7 and Alk-9, were self-pollinated to T4/T6 generations. At T3, the Alk-transgenic lines showed up to 87% reduction in aflatoxin accumulation under laboratory conditions. T4 transgenic Alk-3 and Alk-7 lines, and T5 and T6 Alk-4 and Alk-9 showed an average of 84% reduction in aflatoxin accumulation compared to their null controls under field inoculations (p < 0.05). F1 hybrids of three elite maize inbred lines and the transgenic lines also showed significant improvement in aflatoxin resistance (p < 0.006 to p < 0.045). Reduced A. flavus growth and levels of fungal ß-tubulin DNA were observed in transgenic kernels during in vitro inoculation. Alk-4 transgenic leaf and immature kernel tissues also contained about 1000-fold higher levels of alk-specific small RNAs compared to null controls, indicating that the enhanced aflatoxin resistance in the transgenic maize kernels is due to suppression of A. flavus infection through HIGS of alk gene. Full article
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12 pages, 2960 KiB  
Article
Selection of Atoxigenic Aspergillus flavus for Potential Use in Aflatoxin Prevention in Shandong Province, China
by Jia Xu, Peng Wang, Zehua Zhou, Peter John Cotty and Qing Kong
J. Fungi 2021, 7(9), 773; https://doi.org/10.3390/jof7090773 - 18 Sep 2021
Cited by 6 | Viewed by 2723
Abstract
Aspergillus flavus is a common filamentous fungus widely present in the soil, air, and in crops. This facultative pathogen of both animals and plants produces aflatoxins, a group of mycotoxins with strong teratogenic and carcinogenic properties. Peanuts are highly susceptible to aflatoxin contamination [...] Read more.
Aspergillus flavus is a common filamentous fungus widely present in the soil, air, and in crops. This facultative pathogen of both animals and plants produces aflatoxins, a group of mycotoxins with strong teratogenic and carcinogenic properties. Peanuts are highly susceptible to aflatoxin contamination and consumption of contaminated peanuts poses serious threats to the health of humans and domestic animals. Currently, the competitive displacement of aflatoxin-producers from agricultural environments by atoxigenic A. flavus is the most effective method of preventing crop aflatoxin contamination. In the current study, 47 isolates of A. flavus collected from peanut samples originating in Shandong Province were characterized with molecular methods and for aflatoxin-producing ability in laboratory studies. Isolates PA04 and PA10 were found to be atoxigenic members of the L strains morphotype. When co-inoculated with A. flavus NRRL3357 at ratios of 1:10, 1:1, and 10:1 (PA04/PA10: NRRL3357), both atoxigenic strains were able to reduce aflatoxin B1 (AFB1) levels, on both culture media and peanut kernels, by up to 90%. The extent to which atoxigenic strains reduced contamination was correlated with the inoculation ratio. Abilities to compete of PA04 and PA10 were also independently verified against local aflatoxin-producer PA37. The results suggest that the two identified atoxigenic strains are good candidates for active ingredients of biocontrol products for the prevention of aflatoxin contamination of peanuts in Shandong Province. Full article
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Review

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15 pages, 1135 KiB  
Review
Updates on the Functions and Molecular Mechanisms of the Genes Involved in Aspergillus flavus Development and Biosynthesis of Aflatoxins
by Elisabeth Tumukunde, Rui Xie and Shihua Wang
J. Fungi 2021, 7(8), 666; https://doi.org/10.3390/jof7080666 - 17 Aug 2021
Cited by 8 | Viewed by 3392
Abstract
Aspergillus flavus (A. flavus) is a ubiquitous and opportunistic fungal pathogen that causes invasive and non-invasive aspergillosis in humans and animals. This fungus is also capable of infecting a large number of agriculture crops (e.g., peanuts, maze, cotton seeds, rice, etc.), [...] Read more.
Aspergillus flavus (A. flavus) is a ubiquitous and opportunistic fungal pathogen that causes invasive and non-invasive aspergillosis in humans and animals. This fungus is also capable of infecting a large number of agriculture crops (e.g., peanuts, maze, cotton seeds, rice, etc.), causing economic losses and posing serious food-safety concerns when these crops are contaminated with aflatoxins, the most potent naturally occurring carcinogens. In particular, A. flavus and aflatoxins are intensely studied, and they continue to receive considerable attention due to their detrimental effects on humans, animals, and crops. Although several studies have been published focusing on the biosynthesis of the aforementioned secondary metabolites, some of the molecular mechanisms (e.g., posttranslational modifications, transcription factors, transcriptome, proteomics, metabolomics and transcriptome, etc.) involved in the fungal development and aflatoxin biosynthesis in A. flavus are still not fully understood. In this study, a review of the recently published studies on the function of the genes and the molecular mechanisms involved in development of A. flavus and the production of its secondary metabolites is presented. It is hoped that the information provided in this review will help readers to develop effective strategies to reduce A. flavus infection and aflatoxin production. Full article
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