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Plant Disease May 2019In California, aflatoxin contamination of almond, fig, and pistachio has become a serious problem in recent years due to long periods of drought and probably other...
In California, aflatoxin contamination of almond, fig, and pistachio has become a serious problem in recent years due to long periods of drought and probably other climatic changes. The atoxigenic biocontrol product AF36 has been registered for use to limit aflatoxin contamination of pistachio since 2012 and for use in almond and fig since 2017. New biocontrol technologies employ multiple atoxigenic genotypes because those provide greater benefits than using a single genotype. Almond, fig, and pistachio industries would benefit from a multi-strain biocontrol technology for use in these three crops. Several vegetative compatibility groups (VCGs) associated with almond, fig, and pistachio composed exclusively of atoxigenic isolates, including the VCG to which AF36 belongs to, YV36, were previously characterized in California. Here, we report additional VCGs associated with either two or all three crops. Representative isolates of 12 atoxigenic VCGs significantly ( < 0.001) reduced (>80%) aflatoxin accumulation in almond and pistachio when challenged with highly toxigenic isolates of and under laboratory conditions. Isolates of the evaluated VCGs, including AF36, constitute valuable endemic, well-adapted, and efficient germplasm to design a multi-crop, multi-strain biocontrol strategy for use in tree crops in California. Availability of such a strategy would favor long-term atoxigenic communities across the affected areas of California, and this would result in securing domestic and export markets for the nut crop and fig farmer industries and, most importantly, health benefits to consumers.
Topics: Aflatoxins; Aspergillus flavus; California; Ficus; Food Contamination; Microbial Interactions; Pistacia; Prunus dulcis
PubMed: 30807246
DOI: 10.1094/PDIS-08-18-1333-RE -
Behaviour of Aspergillus flavus in presence of Aspergillus niger during biosynthesis of aflatoxin B.Antonie Van Leeuwenhoek Aug 1990Aspergillus niger or Aspergillus tamarii when grown as mixed cultures with toxigenic A. flavus inhibits biosynthesis of aflatoxin by A. flavus, owing primarily to its...
Aspergillus niger or Aspergillus tamarii when grown as mixed cultures with toxigenic A. flavus inhibits biosynthesis of aflatoxin by A. flavus, owing primarily to its ability to produce inhibitors of aflatoxin biosynthesis and to their ability to degrade aflatoxin. Gluconic acid partly prevents aflatoxin production. The other factors such as changes in pH of the medium and the effect on the growth of a. flavus have no role in imparting capabilities to these cultures to inhibit aflatoxin production by A. flavus.
Topics: Aflatoxin B1; Aflatoxins; Aspergillus flavus; Aspergillus niger; Gluconates; Hydrogen-Ion Concentration; Protein Denaturation
PubMed: 2124794
DOI: 10.1007/BF00422728 -
Toxins Sep 2019The calcineurin pathway is an important signaling cascade for growth, sexual development, stress response, and pathogenicity in fungi. In this study, we investigated the...
The calcineurin pathway is an important signaling cascade for growth, sexual development, stress response, and pathogenicity in fungi. In this study, we investigated the function of CrzA, a key transcription factor of the calcineurin pathway, in an aflatoxin-producing fungus . To examine the role of the gene, deletion mutant strains in were constructed and their phenotypes, including fungal growth, spore formation, and sclerotial formation, were examined. Absence of results in decreased colony growth, the number of conidia, and sclerocia production. The -deficient mutant strains were more susceptible to osmotic pressure and cell wall stress than control or complemented strains. Moreover, deletion of results in a reduction in aflatoxin production. Taken together, these results demonstrate that CrzA is important for differentiation and mycotoxin production in .
Topics: Aflatoxins; Aspergillus flavus; Calcineurin; Fungal Proteins
PubMed: 31569747
DOI: 10.3390/toxins11100567 -
MBio Oct 2014G protein-coupled receptors (GPCRs) are transmembrane receptors that relay signals from the external environment inside the cell, allowing an organism to adapt to its...
G protein-coupled receptors (GPCRs) are transmembrane receptors that relay signals from the external environment inside the cell, allowing an organism to adapt to its surroundings. They are known to detect a vast array of ligands, including sugars, amino acids, pheromone peptides, nitrogen sources, oxylipins, and light. Despite their prevalence in fungal genomes, very little is known about the functions of filamentous fungal GPCRs. Here we present the first full-genome assessment of fungal GPCRs through characterization of null mutants of all 15 GPCRs encoded by the aflatoxin-producing fungus Aspergillus flavus. All strains were assessed for growth, development, ability to produce aflatoxin, and response to carbon sources, nitrogen sources, stress agents, and lipids. Most GPCR mutants were aberrant in one or more response processes, possibly indicative of cross talk in downstream signaling pathways. Interestingly, the biological defects of the mutants did not correspond with assignment to established GPCR classes; this is likely due to the paucity of data for characterized fungal GPCRs. Many of the GPCR transcripts were differentially regulated under various conditions as well. The data presented here provide an extensive overview of the full set of GPCRs encoded by A. flavus and provide a framework for analysis in other fungal species. Importance: Aspergillus flavus is an opportunistic pathogen of crops and animals, including humans, and it produces a carcinogenic toxin called aflatoxin. Because of this, A. flavus accounts for food shortages and economic losses in addition to sickness and death. Effective means of combating this pathogen are needed to mitigate its deleterious effects. G protein-coupled receptors (GPCRs) are often used as therapeutic targets due to their signal specificity, and it is estimated that half of all drugs target GPCRs. In fungi such as A. flavus, GPCRs are likely necessary for sensing the changes in the environment, including food sources, developmental signals, stress agents, and signals from other organisms. Therefore, elucidating their functions in A. flavus could identify ideal receptors against which to develop antagonists.
Topics: Aspergillus flavus; Gene Expression Profiling; Gene Knockout Techniques; Genome, Fungal; Metabolic Networks and Pathways; Receptors, G-Protein-Coupled; Stress, Physiological
PubMed: 25316696
DOI: 10.1128/mBio.01501-14 -
BMC Molecular Biology Feb 2019Woronin bodies are fungal-specific organelles whose formation is derived from peroxisomes. The former are believed to be involved in the regulation of mycotoxins...
BACKGROUND
Woronin bodies are fungal-specific organelles whose formation is derived from peroxisomes. The former are believed to be involved in the regulation of mycotoxins biosynthesis, but not in their damage repair function. The hexagonal peroxisome protein (HexA or Hex1) encoded by hexA gene in Aspergillus is the main and the essential component of the Woronin body. However, little is known about HexA in Aspergillus flavus.
RESULTS
In this study, hexA knock-out mutant (ΔhexA) and complementation strain (ΔhexA) were produced using homologous recombination. The results showed that, ΔhexA and ΔhexA were successfully constructed. And the data analysis indicated that the colony diameter, stress sensitivity and the sclerotia formation of A. flavus were nearly not affected by the absence of HexA. Yet, the deletion of hexA gene reduced the production of asexual spores and lessened virulence on peanuts and maize seeds markedly. In addition, it was also found that there was a significant decrease of Aflatoxin B1 production in deletion mutant, when compared to wild type.
CONCLUSIONS
Therefore, it suggested that the hexA gene has an essential function in conidia production and secondary metabolism in A. flavus. The gene is also believed to be playing an important role in the invasion of A. flavus to the host.
Topics: Aflatoxin B1; Arachis; Aspergillus flavus; Fungal Proteins; Gene Deletion; Gene Knockout Techniques; Secondary Metabolism; Seeds; Spores, Fungal; Virulence; Zea mays
PubMed: 30744561
DOI: 10.1186/s12867-019-0121-3 -
Fungal Genetics and Biology : FG & B Jul 2013Aspergillus flavus is a common saprophyte and opportunistic pathogen producing aflatoxin (AF) and many other secondary metabolites. 5-Azacytidine (5-AC), a derivative of...
Aspergillus flavus is a common saprophyte and opportunistic pathogen producing aflatoxin (AF) and many other secondary metabolites. 5-Azacytidine (5-AC), a derivative of the nucleoside cytidine, is widely used for studies in epigenetics and cancer biology as an inactivator of DNA methyltransferase and is also used for studying secondary metabolism in fungi. Our previous studies showed that 5-AC affects development and inhibits AF production in A. flavus, and that A. flavus lacks DNA methylation. In this study, an RNA-Seq approach was applied to explore the mechanism of 5-AC's effect on A. flavus. We identified 240 significantly differentially expressed (Q-value<0.05) genes after 5-AC treatment, including two backbone genes respectively in secondary metabolite clusters #27 and #35. These two clusters are involved in development or survival of sclerotia. GO functional enrichment analysis showed that these significantly differentially expressed genes were mainly involved in catalytic activity and proteolytic functions. The expressed transcripts of most genes in the AF biosynthetic gene cluster in A. flavus showed no significant changes after treatment with 5-AC and were expressed at low levels, and the transcription regulator genes aflR and aflS in this cluster did not show differential expression relative to the sample without 5-AC treatment. We found that the veA gene, which encodes protein bridges VelB and LaeA, decreased profoundly the expressed transcripts, and brlA, which encodes an early regulator of development, increased its transcripts in A. flavus after 5-AC treatment. Our data support a model whereby 5-AC affects development through increasing the expression of brlA by depressing the expression of veA and AF production through suppressing veA expression and dysregulating carboxypeptidase activity, which then prevents the aflatoxisomes (vesicles) from performing their normal function in AF formation. Furthermore, the suppressed veA expression weakens or even interrupts the connection between VelB and LaeA, leading to dysregulation of the expression pattern of genes involved in development and secondary metabolism in A. flavus. The RNA-seq data presented in this work were also served to improve the annotation of the A. flavus genome. This work provides a comprehensive view of the transcriptome of A. flavus responsive to 5-AC and supports the conclusion that fungal development and secondary metabolism are co-regulated.
Topics: Aflatoxins; Aspergillus flavus; Azacitidine; Gene Expression Regulation, Fungal; Transcriptome
PubMed: 23644151
DOI: 10.1016/j.fgb.2013.04.007 -
Toxins Nov 2020The RNA polymerase II (Pol II) transcription process is coordinated by the reversible phosphorylation of its largest subunit-carboxy terminal domain (CTD). Ssu72 is...
The RNA polymerase II (Pol II) transcription process is coordinated by the reversible phosphorylation of its largest subunit-carboxy terminal domain (CTD). Ssu72 is identified as a CTD phosphatase with specificity for phosphorylation of Ser5 and Ser7 and plays critical roles in regulation of transcription cycle in eukaryotes. However, the biofunction of Ssu72 is still unknown in , which is a plant pathogenic fungus and produces one of the most toxic mycotoxins-aflatoxin. Here, we identified a putative phosphatase Ssu72 and investigated the function of Ssu72 in . Deletion of resulted in severe defects in vegetative growth, conidiation and sclerotia formation. Additionally, we found that phosphatase Ssu72 positively regulates aflatoxin production through regulating expression of aflatoxin biosynthesis cluster genes. Notably, seeds infection assays indicated that phosphatase Ssu72 is crucial for pathogenicity of . Furthermore, the Δ mutant exhibited more sensitivity to osmotic and oxidative stresses. Taken together, our study suggests that the putative phosphatase Ssu72 is involved in fungal development, aflatoxin production and pathogenicity in , and may provide a novel strategy to prevent the contamination of this pathogenic fungus.
Topics: Aflatoxins; Aspergillus flavus; Fungal Proteins; Mutation; Phosphoprotein Phosphatases; Stress, Physiological
PubMed: 33202955
DOI: 10.3390/toxins12110717 -
Toxicon : Official Journal of the... Aug 2019Almonds and peanuts are a rich source of proteins, vitamins and unsaturated fatty acids. However, they can be also contaminated by mycotoxigenic fungi; a reason that has...
Almonds and peanuts are a rich source of proteins, vitamins and unsaturated fatty acids. However, they can be also contaminated by mycotoxigenic fungi; a reason that has enhanced to investigate efficient strategies of management of these fungal contaminations. Some Lactic acid bacteria have been proven capable of inhibiting growth and mycotoxin production in livestock and transform it into nontoxic derivatives. In this work, four lactic acid bacteria (LAB) were tested for their abilities to inhibit the growth and mycotoxin production of Aspergillus flavus and Aspergillus carbonarius. Antifungal activity was evaluated in agar medium as well as in almonds and peanuts. Results showed that LAB significantly inhibited Aspergillus flavus and Aspergillus carbonarius in agar medium but none of the strains were able to completely inhibit fungal growth. The highest fungal growth inhibition was obtained using L. kefiri FR7 (51.67% and 45.56% growth inhibition of A. flavus and A. carbonarius, respectively). The cell-free supernatants (CFS) from LAB reduced fungal growth with average growth inhibitions ranging from 13.33% to 40.56% and 12.78% to 37.78% for A. flavus and A. carbonarius, respectively. We noted also that cell-free supernatants at pH7 (CFS-pH7) from the entire tested LAB did not inhibit fungal growth. L. kefiri FR7 was the most effective strain in mycotoxin suppression with a reduction percentage reaching 97.22%, 95.27% and 75.26% for AFB1, AFB2 and OTA respectively. Moreover, the inoculation of L. kefiri FR7 in almonds artificially contaminated with A. flavus decrease 85.27% of AFB1 and 83.94% of AFB2 content after 7 days of incubation. On the other hand, application of L. kefiri FR7 in peanuts artificially contaminated with A. carbonarius reduced OTA content to 25%. Our study revealed the potential use and application of L. kefiri FR7 in the control of fungi growth and mycotoxins production in almonds and peanuts.
Topics: Arachis; Aspergillus; Aspergillus flavus; Biological Control Agents; Food Contamination; Lactobacillaceae; Mycotoxins; Nuts; Prunus dulcis
PubMed: 31095961
DOI: 10.1016/j.toxicon.2019.05.004 -
International Journal of Food... Mar 2002The effects of selected concentrations of antimicrobials from natural (vanillin, thymol, eugenol, carvacrol or citral) or synthetic (potassium sorbate or sodium...
The effects of selected concentrations of antimicrobials from natural (vanillin, thymol, eugenol, carvacrol or citral) or synthetic (potassium sorbate or sodium benzoate) origin on Aspergillus flavus lag time inoculated in laboratory media formulated at water activity (a(w)) 0.99 and pH 4.5 or 3.5, were evaluated. Time to detect a colony with a diameter > 0.5 mm was determined. Mold response was modeled using the Fermi function. Antimicrobial minimal inhibitory concentration (MIC) was defined as the minimal required inhibiting mold growth for 2 months. Fermi function successfully captured A. flavus dose-response curves to the tested antimicrobials with a highly satisfactory fit. Fermi equation coefficients, Pc and k, were used to compare antimicrobials and assess the effect of pH. Important differences in Pc and k were observed among antimicrobials, being natural antimicrobials less pH dependent than synthetic antimicrobials. A large Pc value represents a small antimicrobial effect on A. flavus lag time; thus, high concentrations are needed to delay growth. A. flavus exhibited higher sensitivity to thymol, eugenol, carvacrol, potassium sorbate (at pH 3.5), and sodium benzoate (at pH 3.5) than to vanillin or citral. MICs varied from 200 ppm of sodium bcnzoate at pH 3.5 to 1800 ppm of citral at both evaluated pHs.
Topics: Anti-Infective Agents; Aspergillus flavus; Colony Count, Microbial; Dose-Response Relationship, Drug; Food Preservatives; Hydrogen-Ion Concentration; Microbial Sensitivity Tests; Sorbic Acid; Thymol; Time Factors; Water
PubMed: 11934030
DOI: 10.1016/s0168-1605(01)00639-0 -
Scientific Reports Jan 2024Groundnuts are mostly contaminated with the mold Aspergillus flavus which produces a carcinogenic mycotoxin called as aflatoxin. It is very important to understand the...
Groundnuts are mostly contaminated with the mold Aspergillus flavus which produces a carcinogenic mycotoxin called as aflatoxin. It is very important to understand the genetic factors underlying its pathogenicity, regulation, and biosynthesis of secondary metabolites and animal toxicities, but it still lacks useful information due to certain gaps in the era of modern technology. Therefore, the present study was considered to determine the key genes and metabolites involved in the biosynthesis of aflatoxin by using a molecular approach in a virulent strain of Aspergillus. The whole genome sequence of highly toxic and virulent Aspergillus isolates JAM-JKB-B HA-GG20 revealed 3,73,54,834 bp genome size, 2, 26, 257 number of contigs with N50 value of 49,272 bp, 12,400 genes and 48.1% of GC contained respectively. The genome sequence was compared with other known aflatoxin producing and non-producing genome of Aspergillus spp. and 61 secondary metabolite (SM) gene clusters were annotated with the toxic strain JAM-JKB-BHA-GG20 which showed similarity with other Aspergillus spp. A total number of eight genes (ver-1, AflR, pksA, uvm8, omt1, nor-1, Vha and aflP) were identified related to biosynthesis of aflatoxin and ochratoxin. Also, 69 SSR with forward and reverse primers and 137 di and tri nucleotide motifs were identified in the nucleotide sequence region related to aflatoxin gene pathway. The genes and putative metabolites identified in this study are potentially involved in host invasion and pathogenicity. As such, the genomic information obtained in this study is helpful in understanding aflatoxin gene producing pathway in comparison to other Aspergillus spp. and predicted presence of other secondary metabolites clusters viz. Nrps, T1pks etc. genes associated with a biosynthesis of OTA mycotoxin.
Topics: Aspergillus flavus; Aspergillus; Aflatoxins; Genes, Fungal; Whole Genome Sequencing
PubMed: 38168670
DOI: 10.1038/s41598-023-50986-5