Global population structure and adaptive evolution of aflatoxin-producing fungi.
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PROVIDER: S-EPMC5677503 | BioStudies |
REPOSITORIES: biostudies
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Project description:Aflatoxins are produced by Aspergillus flavus and A. parasiticus in oil-rich seed and grain crops and are a serious problem in agriculture, with aflatoxin B? being the most carcinogenic natural compound known. Sexual reproduction in these species occurs between individuals belonging to different vegetative compatibility groups (VCGs). We examined natural genetic variation in 758 isolates of A. flavus, A. parasiticus and A. minisclerotigenes sampled from single peanut fields in the United States (Georgia), Africa (Benin), Argentina (Córdoba), Australia (Queensland) and India (Karnataka). Analysis of DNA sequence variation across multiple intergenic regions in the aflatoxin gene clusters of A. flavus, A. parasiticus and A. minisclerotigenes revealed significant linkage disequilibrium (LD) organized into distinct blocks that are conserved across different localities, suggesting that genetic recombination is nonrandom and a global occurrence. To assess the contributions of asexual and sexual reproduction to fixation and maintenance of toxin chemotype diversity in populations from each locality/species, we tested the null hypothesis of an equal number of MAT1-1 and MAT1-2 mating-type individuals, which is indicative of a sexually recombining population. All samples were clone-corrected using multi-locus sequence typing which associates closely with VCG. For both A. flavus and A. parasiticus, when the proportions of MAT1-1 and MAT1-2 were significantly different, there was more extensive LD in the aflatoxin cluster and populations were fixed for specific toxin chemotype classes, either the non-aflatoxigenic class in A. flavus or the B?-dominant and G?-dominant classes in A. parasiticus. A mating type ratio close to 1?1 in A. flavus, A. parasiticus and A. minisclerotigenes was associated with higher recombination rates in the aflatoxin cluster and less pronounced chemotype differences in populations. This work shows that the reproductive nature of the population (more sexual versus more asexual) is predictive of aflatoxin chemotype diversity in these agriculturally important fungi.
| S-EPMC3757046 | BioStudies
Project description:Aflatoxins and ochratoxins are among the most important mycotoxins of all and producers of both types of mycotoxins are present in <i>Aspergillus</i> section <i>Flavi</i>, albeit never in the same species. Some of the most efficient producers of aflatoxins and ochratoxins have not been described yet. Using a polyphasic approach combining phenotype, physiology, sequence and extrolite data, we describe here eight new species in section <i>Flavi</i>. Phylogenetically, section <i>Flavi</i> is split in eight clades and the section currently contains 33 species. Two species only produce aflatoxin B<sub>1</sub> and B<sub>2</sub> (<i>A. pseudotamarii</i> and <i>A. togoensis</i>), and 14 species are able to produce aflatoxin B<sub>1</sub>, B<sub>2</sub>, G<sub>1</sub> and G<sub>2</sub>: three newly described species <i>A. aflatoxiformans, A. austwickii</i> and <i>A. cerealis</i> in addition to <i>A. arachidicola</i>, <i>A. minisclerotigenes</i>, <i>A. mottae, A. luteovirescens</i> (formerly <i>A. bombycis</i>)<i>, A. nomius, A. novoparasiticus, A. parasiticus, A. pseudocaelatus, A. pseudonomius, A. sergii</i> and <i>A. transmontanensis</i>. It is generally accepted that <i>A. flavus</i> is unable to produce type G aflatoxins, but here we report on Korean strains that also produce aflatoxin G<sub>1</sub> and G<sub>2</sub>. One strain of <i>A. bertholletius</i> can produce the immediate aflatoxin precursor 3-O-methylsterigmatocystin, and one strain of <i>Aspergillus sojae</i> and two strains of <i>Aspergillus alliaceus</i> produced versicolorins. Strains of the domesticated forms of <i>A. flavus</i> and <i>A. parasiticus</i>, <i>A. oryzae</i> and <i>A. sojae</i>, respectively, lost their ability to produce aflatoxins, and from the remaining phylogenetically closely related species (belonging to the <i>A. flavus</i>-, <i>A. tamarii</i>-, <i>A. bertholletius</i>- and <i>A. nomius</i>-clades), only <i>A. caelatus</i>, <i>A. subflavus</i> and <i>A. tamarii</i> are unable to produce aflatoxins. With exception of <i>A. togoensis</i> in the <i>A. coremiiformis</i>-clade, all species in the phylogenetically more distant clades (<i>A. alliaceus</i>-, <i>A. coremiiformis</i>-, <i>A. leporis</i>- and <i>A. avenaceus</i>-clade) are unable to produce aflatoxins. Three out of the four species in the <i>A. alliaceus</i>-clade can produce the mycotoxin ochratoxin A: <i>A. alliaceus s</i>. <i>str</i>. and two new species described here as <i>A. neoalliaceus</i> and <i>A. vandermerwei</i>. Eight species produced the mycotoxin tenuazonic acid: <i>A. bertholletius</i>, <i>A. caelatus, A. luteovirescens</i>, <i>A. nomius, A. pseudocaelatus</i>, <i>A. pseudonomius, A. pseudotamarii</i> and <i>A. tamarii</i> while the related mycotoxin cyclopiazonic acid was produced by 13 species: <i>A. aflatoxiformans, A. austwickii, A. bertholletius, A. cerealis, A. flavus, A. minisclerotigenes, A. mottae, A. oryzae, A. pipericola, A. pseudocaelatus</i>, <i>A. pseudotamarii, A. sergii</i> and <i>A. tamarii</i>. Furthermore, <i>A. hancockii</i> produced speradine A, a compound related to cyclopiazonic acid. Selected <i>A. aflatoxiformans, A. austwickii, A. cerealis, A. flavus, A. minisclerotigenes, A. pipericola</i> and <i>A. sergii</i> strains produced small sclerotia containing the mycotoxin aflatrem. Kojic acid has been found in all species in section <i>Flavi</i>, except <i>A. avenaceus</i> and <i>A. coremiiformis</i>. Only six species in the section did not produce any known mycotoxins: <i>A. aspearensis</i>, <i>A. coremiiformis, A. lanosus, A. leporis, A. sojae</i> and <i>A. subflavus</i>. An overview of other small molecule extrolites produced in <i>Aspergillus</i> section <i>Flavi</i> is given.
| S-EPMC6080641 | BioStudies
Project description:The Aspergillus parasiticus aflR gene, a gene that may be involved in the regulation of aflatoxin biosynthesis, encodes a putative zinc finger DNA-binding protein. PCR and sequencing were used to examine the presence of aflR homologs in other members of Aspergillus Section Flavi. The predicted amino acid sequences indicated that the same zinc finger domain, CTSCASSKVRCTKEKPACARCIERGLAC, was present in all of the Aspergillus sojae, Aspergillus flavus, and Aspergillus parasiticus isolates examined and in some of the Aspergillus oryzae isolates examined. Unique base substitutions and a specific base deletion were found in the 5' untranslated and zinc finger region; these differences provided distinct fingerprints. A. oryzae and A. flavus had the T-G-A-A-X-C fingerprint, whereas A. parasiticus and A sojae had the C-C-C-C-C-T fingerprint at the corresponding positions. Specific nucleotides at positions -90 (C or T) and -132 (G or A) further distinguished A. flavus from A. oryzae and A. parasiticus from A. sojae, respectively. A sojae ATCC 9362, which was previously designated A. oryzae NRRL 1988, was determined to be a A. sojae strain on the basis of the presence of the characteristic fingerprint, A-C-C-C-C-C-C-T. The DNAs of other members of Aspergillus Section Flavi, such as Aspergillus nomius and Aspergillus tamarii, and some isolates of A. oryzae appeared to exhibit low levels of similarity to the A. parasiticus aflR gene since low amounts of PCR products or no PCR products were obtained when DNAs from these strains were used.
1995-01-01 | S-EPMC167259 | BioStudies
Project description:The presence of molds, especially certain species of <i>Aspergillus</i>, in food commodities may contribute to aflatoxin contamination. The aim of this study was to determine the biodiversity of <i>Aspergillus</i> species in dairy feeds from farms in select locations in Zimbabwe and assess their aflatoxin production potential using a polyphasic approach. A total of 96 feed samples were collected, which consisted of dairy feed concentrate, mixed ration, brewers' spent grain, and grass from 13 farms during the dry season (August-October, 2016) and the following rainy season (January-March, 2017). A total of 199 presumptive isolates representing four sections from genus <i>Aspergillus</i> (<i>Nigri</i>, <i>Fumigati</i>, <i>Flavi</i>, and <i>Circumdati</i>) were recovered from the feeds. Section <i>Flavi</i>, which includes several aflatoxin producers, constituted 23% (<i>n</i> = 46) of the isolates. Species from this section were <i>A. flavus</i>, <i>A. nomius</i>, <i>A. oryzae</i>, <i>A. parasiticus</i>, and <i>A. parvisclerotigenus</i>, and 39 (84.4%) of these showed evidence of aflatoxin production in plate assays. Of the 46 section <i>Flavi</i> isolates examined, some lacked one or more of the five targeted aflatoxin cluster genes (<i>aflD</i>, <i>aflR</i>, <i>aflS</i>, <i>aflM</i>, and <i>aflP</i>). The presence of the five genes was as follows: <i>aflD</i> (76.9%), <i>aflR</i> (48.7%), <i>aflS</i> (74.4%), <i>aflM</i> (64.1%), and <i>aflP</i> (79.5%). This study highlights the species diversity of aflatoxigenic fungi that have the potential to contaminate different types of feed for dairy cows. Our findings underscore the importance of preventing contamination of feedstuffs by these fungi so that aflatoxins do not end up in the diets of consumers.
| S-EPMC7859627 | BioStudies
Project description:Species belonging to <i>Aspergillus</i> section <i>Flavi</i> occur naturally in crops and can cause food spoilage and/or toxin production. The aim of this study was to determine the occurrence and diversity of the species of <i>Aspergillus</i> section <i>Flavi</i> found in wheat and sorghum at harvest time and during silage storage, and to evaluate the toxigenic potential of the isolates to determine the contamination risk of mycotoxins in grains. Strains from <i>Aspergillus flavus</i> and <i>Aspergillus parasiticus</i> were found based on multi-gene phylogenetic analyses. This is the first report on the presence of <i>A. parasiticus</i> in wheat from Uruguay. Of the 80 isolates <i>Aspergillus</i> section <i>Flavi</i>, 30% produced aflatoxins (AFs), mainly type B1, and 25% produced cyclopiazonic acid (CPA). Within the isolates from wheat samples, 35% were AFs producers and 27.5% were CPA producers. Among the <i>Aspergillus</i> section <i>Flavi</i> isolates from sorghum, 25% were AFs producers while 22.5% were CPA producers. This work contributes to the knowledge of the species in crops and helps define appropriate strategies for the prevention and control of contamination with AFs and CPA by <i>Aspergillus</i> section <i>Flavi</i> fungi.
| S-EPMC7448941 | BioStudies
Project description:<label>BACKGROUND</label>Aspergillus arachidicola is an aflatoxigenic fungal species, first isolated from the leaves of a wild peanut species native to Argentina. It has since been reported in maize, Brazil nut and human sputum samples. This aflatoxigenic species is capable of secreting both B and G aflatoxins, similar to A. parasiticus and A. nomius. It has other characteristics that may result in its misidentification as one of several other section Flavi species. This study offers a preliminary analysis of the A. arachidicola genome.<label>RESULTS</label>In this study we sequenced the genome of the A. arachidicola type strain (CBS 117610) and found its genome size to be 38.9 Mb, and its number of predicted genes to be 12,091, which are values comparable to those in other sequenced Aspergilli. A comparison of 57 known Aspergillus secondary metabolite gene clusters, among closely-related aflatoxigenic species, revealed nearly half were predicted to exist in the type strain of A. arachidicola. Of its predicted genes, 691 were identified as unique to the species and 60% were assigned Gene Ontology terms using BLAST2GO. Phylogenomic inference shows CBS 117610 sharing a most recent common ancestor with A. parasiticus. Finally, BLAST query of A. flavus mating-type idiomorph sequences to this strain revealed the presence of a single mating-type (MAT1-1) idiomorph.<label>CONCLUSIONS</label>Based on A. arachidicola morphological, genetic and chemotype similarities with A. flavus and A. parasiticus, sequencing the genome of A. arachidicola will contribute to our understanding of the evolutionary relatedness among aflatoxigenic fungi.
| S-EPMC5845213 | BioStudies
Project description:Biocontrol using non-aflatoxigenic strains of Aspergillus flavus has the greatest potential to mitigate aflatoxin contamination in agricultural produce. However, factors that influence the efficacy of biocontrol agents in reducing aflatoxin accumulation under field conditions are not well-understood. Shifts in the genetic structure of indigenous soil populations of A. flavus following application of biocontrol products Afla-Guard and AF36 were investigated to determine how these changes can influence the efficacy of biocontrol strains in reducing aflatoxin contamination. Soil samples were collected from maize fields in Alabama, Georgia, and North Carolina in 2012 and 2013 to determine changes in the population genetic structure of A. flavus in the soil following application of the biocontrol strains. A. flavus L was the most dominant species of Aspergillus section Flavi with a frequency ranging from 61 to 100%, followed by Aspergillus parasiticus that had a frequency of <35%. The frequency of A. flavus L increased, while that of A. parasiticus decreased after application of biocontrol strains. A total of 112 multilocus haplotypes (MLHs) were inferred from 1,282 isolates of A. flavus L using multilocus sequence typing of the trpC, mfs, and AF17 loci. A. flavus individuals belonging to the Afla-Guard MLH in the IB lineage were the most dominant before and after application of biocontrol strains, while individuals of the AF36 MLH in the IC lineage were either recovered in very low frequencies or not recovered at harvest. There were no significant (P > 0.05) differences in the frequency of individuals with MAT1-1 and MAT1-2 for clone-corrected MLH data, an indication of a recombining population resulting from sexual reproduction. Population mean mutation rates were not different across temporal and spatial scales indicating that mutation alone is not a driving force in observed multilocus sequence diversity. Clustering based on principal component analysis identified two distinct evolutionary lineages (IB and IC) across all three states. Additionally, patristic distance analysis revealed phylogenetic incongruency among single locus phylogenies which suggests ongoing genetic exchange and recombination. Levels of aflatoxin accumulation were very low except in North Carolina in 2012, where aflatoxin levels were significantly (P < 0.05) lower in grain from treated compared to untreated plots. Phylogenetic analysis showed that Afla-Guard was more effective than AF36 in shifting the indigenous soil populations of A. flavus toward the non-toxigenic or low aflatoxin producing IB lineage. These results suggest that Afla-Guard, which matches the genetic and ecological structure of indigenous soil populations of A. flavus in Alabama, Georgia, and North Carolina, is likely to be more effective in reducing aflatoxin accumulation and will also persist longer in the soil than AF36 in the southeastern United States.
| S-EPMC6685141 | BioStudies
Project description:BACKGROUND: Aspergillus flavus is intensively studied for its role in infecting crop plants and contaminating produce with aflatoxin, but its role as a human pathogen is less well understood. In parts of the Middle East and India, A. flavus surpasses A. fumigatus as a cause of invasive aspergillosis and is a significant cause of cutaneous, sinus, nasal and nail infections. METHODS: A collection of 45 clinical and 10 environmental A. flavus isolates from Iran were analysed using Variable-Number Tandem-Repeat (VNTR) markers with MICROSAT and goeBURST to determine their genetic diversity and their relatedness to clinical and environmental A. flavus isolates from Australia. Phylogeny was assessed using partial ?-tubulin and calmodulin gene sequencing, and mating type was determined by PCR. Antifungal susceptibility testing was performed on selected isolates using a reference microbroth dilution method. RESULTS: There was considerable diversity in the A. flavus collection, with no segregation on goeBURST networks according to source or geographic location. Three Iranian isolates, two from sinus infections and one from a paranasal infection grouped with Aspergillus minisclerotigenes, and all produced B and G aflatoxin. Phylogenic analysis using partial ?-tubulin and calmodulin sequencing confirmed two of these as A. minisclerotigenes, while the third could not be differentiated from A. flavus and related species within Aspergillus section flavi. Based on epidemiological cut-off values, the A. minisclerotigens and A. flavus isolates tested were susceptible to commonly used antifungal drugs. CONCLUSIONS: This is the first report of human infection due to A. minisclerotigenes, and it raises the possiblity that other species within Aspergillus section flavi may also cause clinical disease. Clinical isolates of A. flavus from Iran are not distinct from Australian isolates, indicating local environmental, climatic or host features, rather than fungal features, govern the high incidence of A. flavus infection in this region. The results of this study have important implications for biological control strategies that aim to reduce aflatoxin by the introduction of non-toxigenic strains, as potentially any strain of A. flavus, and closely related species like A. minisclerotigenes, might be capable of human infection.
| S-EPMC4099206 | BioStudies
Project description:Aflatoxins (AFs) are secondary metabolites produced by Aspergillus section Flavi during their development, particularly in maize. It is widely accepted that AFB1 is a major contaminant in regions where hot climate conditions favor the development of aflatoxigenic species. Global warming could lead to the appearance of AFs in maize produced in Europe. This was the case in 2015, in France, when the exceptionally hot and dry climatic conditions were favorable for AF production. Our survey revealed AF contamination of 6% (n = 114) of maize field samples and of 15% (n = 81) of maize silo samples analyzed. To understand the origin of the contamination, we characterized the mycoflora in contaminated samples and in samples produced in the same geographic and climatic conditions but with no AFs. A special focus was placed on Aspergillus section Flavi. A total of 67 strains of Aspergillus section Flavi were isolated from the samples. As expected, the strains were observed in all AF+ samples and, remarkably, also in almost 40% of AF- samples, demonstrating the presence of these potent toxin producers in fields in France. A. flavus was the most frequent species of the section Flavi (69% of the strains). But surprisingly, A. parasiticus was also a frequent contaminant (28% of the strains), mostly isolated from AF+ samples. This finding is in agreement with the presence of AFG in most of those samples.
| S-EPMC6315360 | BioStudies
Project description:A novel genetic approach for classifying the species of Aspergillus Section Flavi is described here. This approach consists of PCR amplification of the 5.8S ribosomal DNA-intervening internal transcribed spacer regions (ITS I-5.8S-ITS II) with universal primers and of analysis of the PCR product by the principle of single-strand conformation polymorphism (SSCP). The approximately 570- to 590-bp PCR products were denatured and subjected to electrophoresis on a polyacrylamide gel supplemented with 20% formamide. The SSCP patterns of these species became more distinct by the addition of formamide to the gel and by visualization with ethidium bromide staining. A little interspecific length polymorphism among amplified ribosomal DNAs was enhanced to be detected by PCR-SSCP analysis. This analysis was capable of classifying 67 of the 68 Aspergillus Section Flavi strains tested into the following four groups, regardless of origin: A. flavus/A. oryzae, A. parasiticus/A. sojae, A. tamarii, and A. nomius. The results of restriction fragment length polymorphism analysis with PCR products of the ITS regions were consistent with those of PCR-SSCP analysis, except for A. nomius, which was not clearly differentiated from A. parasiticus/A. sojae. Nonradiolabelled PCR-SSCP analysis is inexpensive and practical to perform without special apparatus or skill and should assist in fungal morphological identification.
1996-01-01 | S-EPMC168082 | BioStudies